<PAGE>
                                  SCHEDULE 14A
                                 (RULE 14A-101)
 
                    INFORMATION REQUIRED IN PROXY STATEMENT
 
                            SCHEDULE 14A INFORMATION
 
                PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE
                        SECURITIES EXCHANGE ACT OF 1934
 

<TABLE>
<S>        <C>
Filed by the Registrant /X/
Filed by a Party other than the Registrant / /
 
Check the appropriate box:
/X/        Preliminary Proxy Statement
/ /        Confidential, for Use of the Commission Only (as permitted
           by Rule 14a-6(e)(2))
/ /        Definitive Proxy Statement
/ /        Definitive Additional Materials
/ /        Soliciting Material Pursuant to Rule 14a-11(c) or Rule
           14a-12
 
              ALEXION PHARMACEUTICALS, INC.
-----------------------------------------------------------------------
           (Name of Registrant as Specified In Its Charter)
 
-----------------------------------------------------------------------
     (Name of Person(s) Filing Proxy Statement, if other than the
                              Registrant)
</TABLE>

 
Payment of Filing Fee (Check the appropriate box):
 

<TABLE>
<S>        <C>  <C>
/X/        No fee required.
/ /        Fee computed on table below per Exchange Act Rules 14a-6(i)(1)
           and 0-11.
           (1)  Title of each class of securities to which transaction
                applies:
                ----------------------------------------------------------
           (2)  Aggregate number of securities to which transaction
                applies:
                ----------------------------------------------------------
           (3)  Per unit price or other underlying value of transaction
                computed pursuant to Exchange Act Rule 0-11 (set forth the
                amount on which the filing fee is calculated and state how
                it was determined):
                ----------------------------------------------------------
           (4)  Proposed maximum aggregate value of transaction:
                ----------------------------------------------------------
           (5)  Total fee paid:
                ----------------------------------------------------------
 
/ /        Fee paid previously with preliminary materials.
 
/ /        Check box if any part of the fee is offset as provided by
           Exchange Act Rule 0-11(a)(2) and identify the filing for which
           the offsetting fee was paid previously. Identify the previous
           filing by registration statement number, or the Form or
           Schedule and the date of its filing.
 
           (1)  Amount Previously Paid:
                ----------------------------------------------------------
           (2)  Form, Schedule or Registration Statement No.:
                ----------------------------------------------------------
           (3)  Filing Party:
                ----------------------------------------------------------
           (4)  Date Filed:
                ----------------------------------------------------------
</TABLE>


<PAGE>
                         ALEXION PHARMACEUTICALS, INC.
                                25 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
                                 (203) 776-1790
 
                            ------------------------
 
October 30, 2000
 
Dear Fellow Stockholder:
 
    You are cordially invited to attend the Company's Annual Meeting of
Stockholders to be held at 10:00 a.m., on Friday December 8, 2000, at the Park
Avenue Room at the Hotel Inter-Continental, 111 East 48th Street, New York, New
York 10017.
 
    This year, you are being asked:
 
    (1) To elect seven directors to the Company's Board of Directors,
       constituting the entire Board to serve for the ensuing year;
 
    (2) To approve an amendment to the Company's 1992 Stock Option Plan for
       Outside Directors;
 
    (3) To ratify the adoption of the Company's 2000 Stock Option Plan;
 
    (4) To approve an amendment to the Company's Certificate of Incorporation to
       increase the Company's authorized shares from 30,000,000 shares to
       100,000,000 shares; and
 
    (5) To ratify the appointment of Arthur Andersen LLP as the Company's
       independent public accountants.
 
    In addition, I will be pleased to report on the affairs of the Company and a
discussion period will be provided for questions and comments of general
interest to stockholders.
 
    We look forward to greeting personally those stockholders who are able to be
present at the meeting; however, whether or not you plan to be with us at the
meeting, it is important that your shares be represented. Accordingly, you are
requested to sign and date the enclosed proxy and mail it in the envelope
provided at your earliest convenience.
 
    Thank you for your cooperation.
 
                                          Very truly yours,
                                          Leonard Bell, M.D.
                                          PRESIDENT, CHIEF EXECUTIVE OFFICER,
                                          SECRETARY AND TREASURER

<PAGE>
                         ALEXION PHARMACEUTICALS, INC.
                             NEW HAVEN, CONNECTICUT
 
                            ------------------------
 
                    NOTICE OF ANNUAL MEETING OF STOCKHOLDERS
                                OCTOBER 30, 2000
 
                            ------------------------
 
    Notice is hereby given that the Annual Meeting of Stockholders of Alexion
Pharmaceuticals, Inc. will be held on Friday December 8, 2000, at 10:00 a.m., at
the Park Avenue Room at the Hotel Inter-Continental, 111 East 48th Street, New
York, New York 10017 for the following purposes:
 
    (1) To elect seven directors to the Company's Board of Directors,
       constituting the entire Board to serve for the ensuing year;
 
    (2) To consider and vote upon a proposal to amend the Company's 1992 Stock
       Option Plan for Outside Directors;
 
    (3) To consider and vote upon a proposal to ratify the adoption of the
       Company's 2000 Stock Option Plan;
 
    (4) To consider and vote upon a proposal to amend the Company's Certificate
       of Incorporation to increase the Company's authorized shares from
       30,000,000 shares to 100,000,000 shares;
 
    (5) To ratify the appointment of Arthur Andersen LLP as the Company's
       independent public accountants; and
 
    (6) To transact such other business as may properly come before the Annual
       Meeting or any adjournment thereof.
 
    Stockholders of record at the close of business on October 26, 2000 will be
entitled to notice of and to vote at the Annual Meeting or any adjournment
thereof.
 
    All stockholders are cordially invited to attend the Annual Meeting in
person. Stockholders who are unable to attend the Annual Meeting in person are
requested to complete and date the enclosed form of proxy and return it promptly
in the envelope provided. No postage is required if mailed in the United States.
Stockholders who attend the Annual Meeting may revoke their proxy and vote their
shares in person.
 
                                          Leonard Bell, M.D.
                                          SECRETARY

<PAGE>
                         ALEXION PHARMACEUTICALS, INC.
                                25 SCIENCE PARK
                          NEW HAVEN, CONNECTICUT 06511
 
                            ------------------------
 
                                PROXY STATEMENT
 
                             ---------------------
 
                              GENERAL INFORMATION
 
PROXY SOLICITATION
 
    This Proxy Statement is furnished to the holders of Common Stock, par value
$.0001 per share (the "Common Stock"), of Alexion Pharmaceuticals, Inc. (the
"Company") in connection with the solicitation by the Board of Directors of the
Company of proxies for use at the Annual Meeting of Stockholders to be held on
Friday, December 8, 2000, at 10:00 a.m., at the Park Avenue Room at the Hotel
Inter-Continental, 111 East 48th Street, New York, New York 10017 or at any
adjournment thereof, pursuant to the accompanying Notice of Annual Meeting of
Stockholders. The purposes of the meeting and the matters to be acted upon are
set forth in the accompanying Notice of Annual Meeting of Stockholders. The
Board of Directors is not currently aware of any other matters which will come
before the meeting.
 
    Proxies will be mailed to stockholders on or about October 30, 2000 and will
be solicited chiefly by mail. The Company will make arrangements with brokerage
houses and other custodians, nominees and fiduciaries to send proxies and proxy
materials to the beneficial owners of the shares and will reimburse them for
their expenses in so doing. Should it appear desirable to do so in order to
ensure adequate representation of shares at the meeting, officers, agents and
employees of the Company may communicate with stockholders, banks, brokerage
houses and others by telephone, facsimile, email or in person to request that
proxies be furnished. All expenses incurred in connection with this solicitation
will be borne by the Company. The Company has no present plans to hire special
employees or paid solicitors to assist in obtaining proxies, but reserves the
option of doing so if it should appear that a quorum otherwise might not be
obtained.
 
REVOCABILITY AND VOTING OF PROXY
 
    A form of proxy for use at the Annual Meeting of Stockholders and a return
envelope for the proxy are enclosed. Stockholders may revoke the authority
granted by their execution of proxies at any time before their effective
exercise by filing with the Secretary of the Company a written notice of
revocation or a duly executed proxy bearing a later date, or by voting in person
at the meeting. Shares of the Company's Common Stock represented by executed and
unrevoked proxies will be voted in accordance with the choice or instructions
specified thereon. If no specifications are given, the proxies intend to vote
the shares represented thereby for all listed nominees for director, for the
amendment to the Company's 1992 Stock Option Plan for Outside Directors, for the
approval of the Company's 2000 Stock Option Plan, for the amendment to the
Company's Certificate of Incorporation, for ratification of the appointment of
Arthur Andersen LLP as the Company's independent public accountants, and in
accordance with their best judgment on any other matters which may properly come
before the meeting.
 
RECORD DATE AND VOTING RIGHTS
 
    Only stockholders of record at the close of business on October 26, 2000 are
entitled to notice of and to vote at the Annual Meeting or any and all
adjournments thereof. On October 26, 2000 there were       shares of Common
Stock outstanding; each such share is entitled to one vote on each of

<PAGE>
the matters to be presented at the Annual Meeting. The holders of a majority of
the outstanding shares of Common Stock, present in person or by proxy and
entitled to vote, will constitute a quorum at the Annual Meeting. Abstentions
and broker non-votes will be counted for purposes of determining the presence or
absence of a quorum. "Broker non-votes" are shares held by brokers or nominees
which are present in person or represented by proxy, but which are not voted on
a particular matter because instructions have not been received from the
beneficial owner. Under applicable Delaware law, the effect of broker non-votes
on a particular matter depends on whether the matter is one as to which the
broker or nominee has discretionary voting authority under the applicable rule
of the New York Stock Exchange. The effect of broker non-votes on the specific
items to be brought before the Annual Meeting is discussed under each item.
 
                      BENEFICIAL OWNERSHIP OF COMMON STOCK
 
    The following table sets forth certain information as of October 1, 2000
(except as otherwise noted in the footnotes) regarding the beneficial ownership
(as defined by the Securities and Exchange Commission (the "SEC")) of the
Company's Common Stock of: (i) each person known by the Company to own
beneficially more than five percent of the Company's outstanding Common Stock;
(ii) each director (see "Proposal No.1--Election of Directors") (iii) each
executive officer named in the Summary Compensation Table; and (iv) all
directors and executive officers of the Company as a group. Except as otherwise
specified, the named beneficial owner has the sole voting and investment power
over the shares listed.
 

<TABLE>
<CAPTION>
                                                              NUMBER OF SHARES     PERCENTAGE OF
NAME AND ADDRESS                                                BENEFICIALLY     OUTSTANDING SHARES
OF BENEFICIAL OWNER(1)                                            OWNED(2)        OF COMMON STOCK
----------------------                                        ----------------   ------------------
<S>                                                           <C>                <C>
BB Biotech AG Vordergrasse 3
8200 Schaffhausen
CH/Switzerland(3)...........................................     1,824,113              11.8%
 
Scudder Kemper Investments, Inc.
345 Park Avenue
New York, NY 10154(4).......................................     1,615,000              10.4%
 
Janus Capital Corporation
100 Fillmore Street, Suite 400
Denver, Colorado 80206-4923(5)..............................     1,185,695               7.7%
 
Franklin Advisors, Inc.
777 Mariners Island Blvd, 7th Flr
San Mateo, CA 94404(6)......................................     1,004,500               6.5%
 
AMVESCAP, PLC
1315 Peachtree Street, NE
Atlanta, GA 30309(7)........................................       871,640               5.6%
 
The Kaufmann Fund, Inc.
140 E. 45th Street, 43rd Flr
New York, NY 10017(8).......................................       837,300               5.4%
 
Leonard Bell, M.D.(9).......................................       698,434               4.4%
 
Stephen P. Squinto, Ph.D.(10)...............................       202,950               1.3%
 
David W. Keiser(11).........................................       197,175               1.3%
 
John H. Fried, Ph.D.(12)....................................        92,336                 *
</TABLE>

 
                                       2

<PAGE>
 

<TABLE>
<CAPTION>
                                                              NUMBER OF SHARES     PERCENTAGE OF
NAME AND ADDRESS                                                BENEFICIALLY     OUTSTANDING SHARES
OF BENEFICIAL OWNER(1)                                            OWNED(2)        OF COMMON STOCK
----------------------                                        ----------------   ------------------
<S>                                                           <C>                <C>
Joseph Madri, Ph.D., M.D.(13)...............................        58,800                 *
 
Max Link, Ph.D.(14).........................................        26,823                 *
 
Leonard Marks, Jr., Ph.D.(15)...............................        17,300                 *
 
Nancy Motola, Ph.D.(16).....................................         8,875                 *
 
Jerry T. Jackson(17)........................................         2,500                 *
 
R. Douglas Norby(18)........................................         2,500                 *
 
Alvin S. Parven(19).........................................         1,400                 *
 
All Directors and Executive Officers as a group (13
persons)(20)................................................     1,430,236               8.7%
</TABLE>

 
------------------------
 
   * Less than one percent.
 
 (1) Unless otherwise indicated, the address of all persons is 25 Science Park,
     Suite 360, New Haven, Connecticut 06511.
 
 (2) To the Company's knowledge, except as set forth below, the persons named in
     the table have sole voting and investment power with respect to all shares
     of Common Stock shown as beneficially owned by them, subject to community
     property laws where applicable and the information contained in the
     footnotes in this table.
 
 (3) This figure is based upon information set forth in Amendment No. 3 to
     Schedule 13D dated May 27, 1998, filed jointly by BB Biotech AG and Biotech
     Target, S.A. Biotech Target, S.A., a Panamanian corporation, is a
     wholly-owned subsidiary of BB Biotech AG. BB Biotech AG is a holding
     company incorporated in Switzerland. BB Biotech AG disclosed that it may be
     deemed to share with Biotech Target, S.A. the voting and dispositive power
     with respect to these shares.
 
 (4) This figure is based upon information set forth in Schedule 13G dated
     December 10, 1999. Scudder disclosed that it has shared voting power with
     respect to 154,000 shares. Scudder disclaims beneficial ownership of the
     shares held by it.
 
 (5) This figure is based upon information set forth in Schedule 13F dated
     April 14, 2000.
 
 (6) This figure is based upon information disclosed to the Company by Franklin
     Advisers, Inc. representing its ownership as of September 18, 2000.
 
 (7) This figure is based upon information disclosed to the Company by AMVESCAP,
     PLC representing its ownership as of August 31, 2000.
 
 (8) This figure is based upon information set forth in Schedule 13G dated
     June 8, 2000.
 
 (9) Includes 538,334 shares of Common Stock that may be acquired upon the
     exercise of options within 60 days of October 1, 2000 and 300 shares, in
     aggregate, held in the names of Dr. Bell's three minor children. Excludes
     146,666 shares obtainable through the exercise of options, granted to
     Dr. Bell, which are not exercisable within 60 days of October 1, 2000 and
     90,000 shares held in trust for Dr. Bell's children of which Dr. Bell
     disclaims beneficial ownership. Dr. Bell disclaims beneficial ownership of
     the shares held in the name of his minor children.
 
 (10) Includes 151,250 shares of Common Stock which may be acquired upon the
      exercise of options within 60 days of October 1, 2000 and 6,200 shares, in
      aggregate, held in the names of Dr. Squinto's two minor children of which
      6,000 shares are in two trusts managed by his wife. Excludes 51,250 shares
      obtainable through the exercise of options, granted to Dr. Squinto, which
 
                                       3

<PAGE>
      are not exercisable within 60 days of October 1, 2000. Dr. Squinto
      disclaims beneficial ownership of the shares held in the name of his minor
      children and the foregoing trusts.
 
 (11) Includes 161,875 shares of Common Stock which may be acquired upon the
      exercise of options within 60 days of October 1, 2000 and 300 shares, in
      aggregate, held in the names of Mr. Keiser's three minor children.
      Excludes 65,625 shares obtainable through the exercise of options, granted
      to Mr. Keiser, which are not exercisable within 60 days of October 1,
      2000. Mr. Keiser disclaims beneficial ownership of the shares held in the
      name of his minor children.
 
 (12) Excludes 14,000 shares obtainable through the exercise of options granted
      to Dr. Fried, which are not exercisable within 60 days of October 1, 2000.
 
 (13) Includes 13,800 shares of Common Stock which may be acquired on the
      exercise of options that are exercisable within 60 days of October 1,
      2000. Excludes 14,000 obtainable through the exercise of options granted
      to Dr. Madri, which are not exercisable within 60 days of October 1, 2000.
 
 (14) Includes 1,500 shares of Common Stock which may be acquired upon the
      exercise of options within 60 days of October 1, 2000. Excludes 14,000
      shares obtainable through the exercise of options, granted to Dr. Link,
      which are not exercisable within 60 days of October 1, 2000.
 
 (15) Includes 16,300 shares of Common Stock which may be acquired upon the
      exercise of options within 60 days of October 1, 2000. Excludes 14,000
      shares obtainable through the exercise of options granted to Dr. Marks,
      which are not exercisable within 60 days of October 1, 2000.
 
 (16) Includes 8,875 shares of Common Stock, which may be acquired upon the
      exercise of options within 60 days of October 1, 2000. Excludes 53,125
      shares obtainable through the exercise of options, granted to Dr. Motola,
      which are not exercisable within 60 days of October 1, 2000.
 
 (17) Includes 2,500 shares of Common Stock which may be acquired on the
      exercise of options that are exercisable within 60 days of October 1,
      2000. Excludes 17,000 shares obtainable through the exercise of options
      granted to Mr. Jackson, which are not exercisable within 60 days of
      October 1, 2000.
 
 (18) Includes 2,500 shares of Common Stock which may be acquired on the
      exercise of options that are exercisable within 60 days of October 1,
      2000. Excludes 17,000 shares obtainable through the exercise of options
      granted to Mr. Norby, which are not exercisable within 60 days of
      October 1, 2000.
 
 (19) Includes 1,400 shares of Common Stock which may be acquired on the
      exercise of options that are exercisable within 60 days of October 1,
      2000. Excludes 17,000 shares obtainable through the exercise of options
      granted to Mr. Parven, which are not exercisable within 60 days of
      October 1, 2000.
 
 (20) Consists of shares beneficially owned by Drs. Bell, Fried, Link, Madri,
      Marks, Motola, Squinto and Messrs. Jackson, Keiser, Norby and Parven, and
      certain other officers. Includes 978,061 shares of Common Stock, which may
      be acquired upon the exercise of options within 60 days of October 1,
      2000.
 
                                       4

<PAGE>
                     PROPOSAL NO. 1--ELECTION OF DIRECTORS
 
    The Board of Directors presently has eight members. Leonard
Marks, Jr. Ph.D., a director and member of the Audit Committee, will serve only
until the Annual Meeting. Seven directors (constituting the entire Board) are to
be elected at the Annual Meeting. Unless otherwise specified, the enclosed proxy
will be voted in favor of the persons named below to serve until the next annual
meeting of stockholders and until their successors shall have been duly elected
and shall qualify. In the event any of these nominees shall be unable to serve
as a director, the shares represented by the proxy will be voted for the person,
if any, who is designated by the Board of Directors to replace the nominee. All
nominees have consented to be named and have indicated their intent to serve if
elected. The Board of Directors has no reason to believe that any of the
nominees will be unable to serve or that any vacancy on the Board of Directors
will occur.
 
    The nominees, their ages, the year in which each first became a director and
their principal occupations or employment during the past five years are:
 

<TABLE>
<CAPTION>
                                                   YEAR FIRST
                                                     BECAME
DIRECTOR                                  AGE       DIRECTOR    PRINCIPAL OCCUPATION DURING THE PAST FIVE YEARS
--------                                --------   ----------   -----------------------------------------------
<S>                                     <C>        <C>          <C>
John H. Fried, Ph.D.(1)(2)(3).........     70         1992      Chairman of the Board of Directors of the
                                                                Company since April 1992; President of Fried &
                                                                Co., Inc. since 1992; Chairman of the Board of
                                                                Corvas International Inc. from 1997 to 1999;
                                                                Vice Chairman of Syntex Corp. from 1985 to
                                                                January 1993 and President of the Syntex
                                                                Research Division from 1976 to 1992.
 
Leonard Bell, M.D.(1).................     42         1992      President, Chief Executive Officer, Secretary,
                                                                Treasurer and director of the Company since
                                                                January 1992; Assistant Professor of Medicine
                                                                and Pathology and Co-Director of the Program in
                                                                Vascular Biology at the Yale University School
                                                                of Medicine from 1991 to 1992; Attending
                                                                Physician at the Yale-New Haven Hospital and
                                                                Assistant Professor of the Department of
                                                                Internal Medicine at the Yale University School
                                                                of Medicine from 1990 through 1992; Serves as
                                                                director of The Medicine Company.
 
Jerry T. Jackson(3)...................     59         1999      Retired since 1995; Executive Vice President of
                                                                Merck from 1993 to 1995; serves as director of
                                                                Cor Therapeutics, Inc., Molecular Biosystems,
                                                                Inc., and Crescendo Pharmaceuticals
                                                                Corporation.
</TABLE>

 
                                       5

<PAGE>
 

<TABLE>
<CAPTION>
                                                   YEAR FIRST
                                                     BECAME
DIRECTOR                                  AGE       DIRECTOR    PRINCIPAL OCCUPATION DURING THE PAST FIVE YEARS
--------                                --------   ----------   -----------------------------------------------
<S>                                     <C>        <C>          <C>
Max Link, Ph.D.(1)(2)(3)..............     60         1992      Retired; Chief Executive Officer of Corange
                                                                (Bermuda) from May 1993 to June 1994; Chairman
                                                                of the Board of Sandoz Pharma, Ltd. From 1992
                                                                to 1993 and Chief Executive Officer of Sandoz
                                                                Pharma, Ltd. from 1987 to 1992; serves as
                                                                director of Protein Design Labs, Inc., Cell
                                                                Therapeutics, Inc., Procept, Inc., Human Genome
                                                                Sciences, Inc., Access Pharmaceuticals, Inc.,
                                                                Discovery Labs, Inc. and Celsian Corporation.
 
Joseph A. Madri, Ph.D., M.D...........     54         1992      Faculty Member of the Yale University School of
                                                                Medicine since 1980.
 
R. Douglas Norby(2)...................     65         1999      Executive Vice President and Chief Financial
                                                                Officer of LSI Logic Corporation since 1996;
                                                                serves as a director of LSI.
 
Alvin S. Parven(3)....................     60         1999      President of ASP Associates since 1997; Vice
                                                                President at various operating subsidiaries of
                                                                Aetna Insurance Corporation from 1987 to 1997.
</TABLE>

 
------------------------
 
(1) Member of the Nominating Committee of the Board of Directors.
 
(2) Member of the Audit Committee of the Board of Directors.
 
(3) Member of the Compensation Committee of the Board of Directors.
 
    In February 1993, the Board formed an Audit Committee, which was established
to review the internal accounting procedures of the Company and to consult with
and review the Company's independent public accountants and the services
provided by such independent public accountants. Drs. Fried, Link, and Marks,
and Mr. Norby are the current members of the Audit Committee. During the fiscal
year ended July 31, 2000, the Audit Committee held one meeting.
 
    In February 1993, the Board formed a Compensation Committee, which was
established to review compensation practices, to recommend compensation for
executives and key employees, and to administer the Company's non-formula based
stock option plans. Drs. Fried and Link, and Messrs. Jackson and Parven are the
current members of the Compensation Committee. During the fiscal year ended
July 31, 2000, the Compensation Committee held two meetings.
 
    In June 1999, the Board formed a Nominating Committee, which was established
to review and recommend new directors to the Board. The nominating committee
will consider nominees recommended by stockholders; such nominees should be
recommended in accordance with the procedures for submission of stockholder
proposals. Drs. Bell, Fried, and Link are the current members of the Nominating
Committee. During the fiscal year ended July 31, 2000, the Nominating Committee
held one meeting.
 
    During the fiscal year ended July 31, 2000, the Board of Directors held four
meetings and acted by unanimous written consent in lieu of a meeting two times.
Each incumbent director attended at least 75% of the meetings of the Board of
Directors held when he was a director and of all committees of
 
                                       6

<PAGE>
the Board on which he served. Messrs. Jackson and Norby were appointed to the
Board subsequent to July 31, 1999, in September 1999.
 
CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS
 
    In June and October 1992, the Company entered into patent licensing
agreements with Oklahoma Medical Research Foundation ("OMRF") and Yale
University ("Yale"). The agreements provide that the Company will pay to these
institutions royalties based on sales of products incorporating technology
licensed thereunder and also license initiation fees, including annual minimum
royalties that increase in amount based on the status of product development and
the passage of time. Under policies of OMRF and Yale, the individual inventors
of patents are entitled to receive a percentage of the royalties and other
license fees received by the licensing institution. Some of the Company's
founders and scientific advisors, including Dr. Bell, one of the Company's
directors and President and Chief Executive Officer, Dr. Madri, one of the
Company's directors, and Dr. Squinto, its executive Vice President and Head of
Research, and Dr. Rollins, Vice President of Drug Development and Project
Management, are inventors with respect to patent applications licensed from Yale
and, therefore, are entitled to receive a portion of the royalties and other
fees payable by the Company.
 
SECTION 16(a) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE
 
    Section 16(a) of the Exchange Act requires the Company's executive officers
and directors, and persons who beneficially own more than ten percent of the
Company's Common Stock, to file initial reports of ownership and reports of
changes in ownership with the SEC. Executive officers, directors and greater
than ten percent beneficial owners are required by the SEC to furnish the
Company with copies of all Section 16(a) forms they file.
 
    Based upon a review of the copies of such forms furnished to the Company and
written representations from the Company's executive officers and directors, the
Company believes that during fiscal 2000 all Section 16(a) filing requirements
applicable to its executive officers, directors and greater than ten percent
beneficial owners were complied with on a timely basis, except that an annual
report on Form 5 was not timely filed for each of Dr. Joseph Madri and
Mr. Alvin Parven. These annual reports were subsequently filed.
 
VOTE REQUIRED
 
    The seven nominees receiving the highest number of affirmative votes of the
shares present in person or represented by proxy and entitled to vote, a quorum
being present, shall be elected as directors. Only votes cast for a nominee will
be counted, except that the accompanying proxy will be voted for all nominees in
the absence of instruction to the contrary. Abstentions, broker non-votes and
instructions on the accompanying proxy card to withhold authority to vote for
one or more nominees will result in the respective nominees receiving fewer
votes. However, the number of votes otherwise received by the nominee will not
be reduced by such action.
 
THE BOARD OF DIRECTORS DEEMS "PROPOSAL NO. 1--ELECTION OF DIRECTORS" TO BE IN
THE BEST INTERESTS OF THE COMPANY AND ITS STOCKHOLDERS AND RECOMMENDS A VOTE
"FOR" EACH NOMINEE.
 
                                       7

<PAGE>
                             EXECUTIVE COMPENSATION
 
    The following table shows all the cash compensation paid by the Company as
well as certain other compensation paid during the fiscal years indicated to the
Chief Executive Officer of the Company and each of the four other most highly
compensated executive officers of the Company for such period in all capacities
in which they served.
 
                           SUMMARY COMPENSATION TABLE
 

<TABLE>
<CAPTION>
                                                                                                   LONG TERM
                                                                                                  COMPENSATION
                                                         ANNUAL COMPENSATION                      ------------
                                                      --------------------------                    OPTIONS
                                            FISCAL                     BONUS          OTHER        (NUMBER OF
NAME AND PRINCIPAL POSITION                  YEAR     BASE SALARY   COMPENSATION   COMPENSATION     SHARES)
---------------------------                --------   -----------   ------------   ------------   ------------
<S>                                        <C>        <C>           <C>            <C>            <C>
Leonard Bell, M.D.......................     2000       $332,000      $100,000        $4,065(1)      100,000
  President, Chief Executive Officer,        1999        275,000        70,000         4,167(1)       40,000
  Secretary and Treasurer                    1998        250,000        50,000         3,873(1)       60,000
 
David W. Keiser.........................     2000       $205,697      $ 50,000        $4,065(1)       30,000
  Executive Vice President and Chief         1999        190,460        50,000         4,102(1)       22,500
  Operating Officer                          1998        178,000        30,000         3,788(1)       25,000
 
Stephen P. Squinto, Ph.D................     2000       $187,720      $ 35,000            --          20,000
  Executive Vice President and               1999        180,500        25,000            --          17,500
  Head of Research                           1998        165,000        30,000            --          25,000
 
Louis A. Matis, M.D.....................     2000       $187,720      $ 20,000        $4,400(1)           --
  Senior Vice President and Chief            1999        180,500        17,500         4,800(1)       17,500
  Technical Officer(2)                       1998        165,000        30,000         2,400(1)       25,000
 
Nancy Motola, Ph.D......................     2000       $139,050      $ 17,500         3,892(1)       17,500
  Vice-President of Regulatory Affairs       1999         78,519        25,000         1,831(1)       47,500
  and Quality Assurance(3)                   1998             --            --            --              --
</TABLE>

 
------------------------
 
(1) Represents the Company's matching contribution pursuant to its 401(k)
    defined contribution plan.
 
(2) Dr. Matis resigned from the Company in September, 2000.
 
(3) Dr. Motola joined the Company in December, 1998.
 
                                       8

<PAGE>
    The following table sets forth information with respect to option grants in
fiscal year ended July 31, 2000 to the persons named in the Summary Compensation
Table.
 
                       OPTION GRANTS IN LAST FISCAL YEAR
 

<TABLE>
<CAPTION>
                                            % OF TOTAL                                       POTENTIAL REALIZED VALUE AT
                              NUMBER OF      OPTIONS                                           ASSUMED ANNUAL RATES OF
                              SECURITIES    GRANTED TO    EXERCISE    MARKET                 STOCK PRICE APPRECIATION FOR
                              UNDERLYING   EMPLOYEES IN   OR BASE    PRICE ON                       OPTION TERM(3)
                               OPTIONS        FISCAL       PRICE     DATE OF    EXPIRATION   ----------------------------
NAME                          GRANTED(1)     YEAR(2)       ($/SH)     GRANT        DATE         5%($)          10%($)
----                          ----------   ------------   --------   --------   ----------   ------------   -------------
<S>                           <C>          <C>            <C>        <C>        <C>          <C>            <C>
Leonard Bell, M.D...........   100,000(4)      19.1        $64.50     $64.50     07/31/10     $3,893,481     $10,020,265
 
David W. Keiser.............    30,000          5.7         64.50      64.50     07/31/10      1,168,044       3,006,879
 
Stephen P. Squinto, Ph.D....    20,000          3.8         64.50      64.50     07/31/10        778,696       2,004,053
 
Louis A. Matis, M.D.(5).....        --           --            --         --           --             --              --
 
Nancy Motola, Ph.D..........    17,500          3.3         64.50      64.50     07/31/10        681,359       1,753,546
</TABLE>

 
------------------------
 
(1) Options vest in four equal annual installments commencing on the anniversary
    date of the grant unless otherwise indicated.
 
(2) Based upon options to purchase 524,000 shares granted to all employees
    during fiscal year 2000.
 
(3) The 5% and 10% assumed rates of appreciation are specified by the rules of
    the Securities and Exchange Commission and do not represent the Company's
    estimate or projection of the future Common Stock price. There can be no
    assurance that any of the values reflected in the table will be achieved.
 
(4) These options vest in three equal annual installments commencing on the
    anniversary date of the grant.
 
(5) Dr. Matis resigned from the Company in September, 2000.
 
    The following table sets forth information with respect to (i) stock options
exercised in fiscal year 2000 by the persons named in the Summary Compensation
Table and (ii) unexercised stock options held by such individuals at July 31,
2000.
 
                          AGGREGATED OPTION EXERCISES
             IN LAST FISCAL YEAR AND FISCAL YEAR END OPTION VALUES
 

<TABLE>
<CAPTION>
                                                                NUMBER OF UNEXERCISED         VALUE OF UNEXERCISED,
                                   SHARES                          OPTIONS HELD AT           IN-THE-MONEY OPTIONS AT
                                  ACQUIRED                         FISCAL YEAR END            FISCAL YEAR END($)(1)
                                     ON           VALUE      ---------------------------   ---------------------------
NAME                             EXERCISE(#)   REALIZED($)   EXERCISABLE   UNEXERCISABLE   EXERCISABLE   UNEXERCISABLE
----                             -----------   -----------   -----------   -------------   -----------   -------------
<S>                              <C>           <C>           <C>           <C>             <C>           <C>
Leonard Bell, M.D..............         0              0       538,334        146,666      $30,363,786    $2,529,964
 
David W. Keiser................         0              0       161,875         65,625        9,238,125     1,923,750
 
Stephen P. Squinto, Ph.D.......         0              0       151,250         51,250        8,650,938     1,688,125
 
Louis A. Matis, M.D.(2)........         0              0       161,250         31,250        9,262,188     1,688,125
 
Nancy Motola, Ph.D.............     3,000       $118,250         8,875         53,125          469,125     1,873,125
</TABLE>

 
------------------------
 
(1) Based on the average of the high and low sale price of the Common Stock on
    July 31, 2000 of $63.50.
 
(2) Dr. Matis resigned from the Company in September, 2000.
 
                                       9

<PAGE>
EMPLOYMENT AGREEMENTS
 
    Dr. Leonard Bell, President, Chief Executive Officer, Secretary and
Treasurer of the Company, has a three-year employment agreement with the Company
which commenced on April 1, 2000. The agreement provides that Dr. Bell will be
employed as the President and Chief Executive Officer of the Company and that
the Company will use its best efforts to cause Dr. Bell to be elected to the
Board of Directors for the term of the agreement. Dr. Bell currently receives an
annual base salary of $332,000. The contract provides that if (i) Dr. Bell is
dismissed for any reason other than cause (as defined in the employment
agreement) or (ii) Dr. Bell terminates the employment agreement for certain
reasons including (a) certain changes in control of the Company,
(b) Dr. Bell's loss of any material duties or authority, (c) if the Chief
Executive Officer is not the highest ranking officer of the Company, (d) an
uncured material breach of the employment agreement by the Company and (e) the
retention of any senior executive officer by the Company or an offer to pay
compensation to any senior executive of the Company that in either case is
unacceptable to Dr. Bell, in his reasonable judgment, then Dr. Bell shall be
entitled to receive a lump sum cash payment equal to Dr. Bell's annual salary
then in effect multiplied by the number of years remaining in the term of the
employment agreement. In addition, upon such termination, all stock options and
stock awards vest and become immediately exercisable and remain exercisable
through their original terms. If, upon the termination of the employment
agreement on April 1, 2003, Dr. Bell shall cease to be employed by the Company
in the capacity of Chief Executive Officer by reason of the Company's decision
not to continue to employ Dr. Bell as Chief Executive Officer at least on terms
substantially similar to those set forth in the existing employment agreement,
then Dr. Bell will be entitled to a severance payment equal to his annual salary
during the final year of such employment agreement. Similarly, if Dr. Bell is
not able to continue his employment due to a physical or mental incapacity or
disability, all stock options and stock awards held by Dr. Bell prior to his
disability will vest and become immediately exercisable.
 
    Mr. David W. Keiser, Executive Vice-President and Chief Operating Officer,
has a two-year employment agreement with the Company which commenced on
July 17, 2000. Mr. Keiser currently receives an annual base salary of $234,000.
 
    Dr. Stephen P. Squinto, Senior Vice-President and Chief Technical Officer,
has a five-year employment agreement with the Company which commenced in
March 1997. Dr. Squinto currently receives an annual base salary of $206,000.
 
    Dr. Louis A. Matis, Senior Vice President and Chief Scientific Officer, had
a five-year employment agreement with the Company which commenced in
August 1997 under which Dr. Matis received an annual base salary of $187,720.
Dr. Matis resigned from the Company in September, 2000.
 
    Under the employment agreements for each of Mr. Keiser and Dr. Squinto, if
either of them is dismissed for any reason other than cause (as defined in the
employment agreement), death or disability, or if any of them terminates the
employment agreement because of an uncured material breach thereof by the
Company, he shall be entitled to receive a lump sum cash payment equal to the
greater of (a) the annual salary for the remainder of the then current year of
employment and (b) six months salary at the annual rate for the then current
year of employment. In addition, upon such termination, all stock options shall
accelerate vesting such that the number of such options vested on the day of
termination shall be equal to the number of such options vested if the executive
were to have been continuously employed by the Company until the date twelve
months after the date of termination.
 
    All the Company's employment agreements require acknowledgment of the
Company's possession of information created, discovered or developed by the
employee/executive and applicable to the business of the Company and any client,
customer or strategic partner of the Company. Each employee/executive also
agreed to assign all rights he may have or acquire in proprietary information
 
                                       10

<PAGE>
and to keep such proprietary information confidential and also agreed to certain
covenants not to compete with the Company.
 
COMPENSATION OF DIRECTORS
 
    Under the Company's current compensation structure, each non-employee,
member of the Board, other than the Chairman of the Board, is entitled, with 75%
attendance at Board meetings, to receive an annual accrued stipend of up to
$8,000. The Chairman of the Board is entitled, with 75% attendance at Board
meetings, to receive an annual accrued stipend of up to $25,000. Per meeting
fees are paid in the amounts of $1,500 and $750 to the Chairman of the Board and
non-employee members of the Board, respectively. These per meeting fees are
deducted from the maximum annual accrued stipends, which are to be paid in
October of the following year. Each of Drs. Fried, Madri, Marks and Link, and
Messrs. Jackson, Norby and Parven all attended at least 75% of the meetings of
the Company's Board and received their full annual stipend.
 
    The Compensation Committee of the Board of Directors has unanimously
approved an amendment to the Company's compensation structure for its outside
directors. Effective December 8, 2000, the amendment increases the annual
stipend for board members other than the Chairman from $8,000 to $15,000 payable
in quarterly installments. Members of the Board who serve as committee chairs
will be entitled to an additional $2,500 annually. With 75% attendance at Board
meetings, the Chairman of the Board will be entitled to an annual stipend of up
to $30,000.
 
    Under the 1992 Stock Option Plan for Outside Directors, as amended, (the
"Outside Directors' Plan"), each individual who is not an officer, employee or
consultant of the Company or any of its subsidiaries (other than the Chairman of
the Board, who shall be eligible) ("Outside Directors") is automatically granted
an option to purchase 7,500 shares of Common Stock on the date of his or her
initial election to the Board. In addition, on the date of each subsequent
annual meeting of stockholders at which a director is re-elected, such director,
if he or she was still an Outside Director on such date and has attended, either
in person or by telephone, at least seventy-five percent (75%) of the meetings
of the Board of Directors that were held while he or she was a director since
the prior annual meeting of stockholders, is automatically granted an option to
purchase an additional 2,000 shares of the Company's Common Stock. Upon their
re-election to the Board at the last annual meeting, Drs. Fried, Link, Madri and
Marks and Messrs. Jackson, Norby and Parven each received options to purchase
2,000 shares of Common Stock. All options granted under the Outside Directors'
Plan have an exercise price equal to the fair market value on the date of grant
and vest in three equal annual installments beginning on the anniversary date of
the grant.
 
    The Board of Directors unanimously approved, subject to stockholder
approval, an increase in the automatic grants under Outside Directors' Plan.
(See Proposal No. 2). If the stockholders approve such amendments, each Outside
Director will receive an option to purchase 12,000 shares of Common Stock upon
his or her initial election to the Board and each Outside Director will receive
an option to purchase 7,500 shares of Common Stock upon re-election to the
Board, provided he or she has attended at least 75% of the meetings of Board
held while he or she was a director since the prior annual meeting of
stockholders. If Proposal No. 2 is approved by the stockholders, each of Drs.
Fried, Madri and Link and Messrs. Jackson, Norby and Parven will receive an
option to purchase 7,500 shares of Common Stock on December 8, 2000.
 
    The Compensation Committee also approved a one-time grant of options to
purchase 10,000 shares of the Company's Common Stock under the Company's 1992
Stock Option Plan to each of the Outside Directors on July 31, 2000. These
options have an exercise price equal to the fair market value of the Common
Stock on the date of the grant and vest in three equal installments on the
anniversary date of the grant.
 
                                       11

<PAGE>
COMPENSATION COMMITTEE REPORT TO STOCKHOLDERS
 
    The report of the Compensation Committee shall not be deemed incorporated by
reference by any general statement incorporating by reference this proxy
statement into any filing under the Securities Act of 1933, as amended (the
"Securities Act") or under the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), except to the extent that the Company specifically incorporates
this information by reference, and shall not otherwise be deemed filed under
such Acts.
 
    The Compensation Committee is currently comprised of four directors. As
members of the Compensation Committee, it is our responsibility to determine the
most effective total executive compensation strategy based on the Company's
business and consistent with stockholders' interests. Our specific duties entail
reviewing the Company's compensation practices, recommending compensation for
executives and key employees, the making of recommendations to the Board of
Directors with respect to major compensation and benefit programs, and
administering the Company's stock option plans.
 
COMPENSATION PHILOSOPHY
 
    The Company's overall compensation philosophy is to offer competitive
salaries, cash incentives, stock options and benefit plans consistent with the
Company's financial position. Rewarding capable employees who contribute to the
continued success of the Company plus equity participation and a strong
alignment to stockholder's interests are key elements of the Company's
compensation policy. One of the Company's strengths contributing to its success
is the strong management team many of whom have been with the Company for a
significant period of time. The Company's executive compensation policy is to
attract and retain key executives necessary for the Company's short and
long-term success by establishing a direct link between executive compensation
and the performance of the Company by rewarding individual initiative and the
achievement of annual corporate goals through salary and cash bonus awards; and
by providing equity awards based upon present and expected future performance to
allow executives to participate in maximizing shareholder value.
 
    In awarding salary increases and bonuses, the Compensation Committee did not
relate the various elements of corporate performance to each element of
executive compensation. Rather, the Compensation Committee considered whether
the compensation package as a whole adequately compensated each executive for
the Company's performance during the past year and executive's contribution to
such performance.
 
    Under Section 162(m) of the Internal Revenue Code of 1986, as amended (the
"Code"), publicly held companies may be prohibited from deducting as an expense
for federal income tax purposes total remuneration in excess of $1 million paid
to certain executive officers in a single year. However, Section 162(m) provides
an exception for "performance based" remuneration, including renumeration
attributable to certain stock options. The Company expects to keep
"nonperformance based" remuneration within the $1 million limit in order that
all executive compensation will be fully deductible. Nevertheless, although the
Compensation Committee considers the net cost to the Company in making all
compensation decisions (including, for this purpose, the potential limitation on
deductibility of executive compensation), there is no assurance that
compensation realized with respect to any particular award will qualify as
"performance based" remuneration.
 
BASE SALARY
 
    Base salary represents the fixed component of the executive compensation
program. The Company's philosophy regarding base salaries is conservative,
maintaining salaries at approximately competitive industry average.
Determinations of base salary levels are established on an annual review of
marketplace competitiveness with similar biopharmaceutical companies and on
internal relationships. Periodic increases in base salary relate to individual
contributions to the Company's overall performance, relative marketplace
competitiveness levels, length of service and the industry's annual
 
                                       12

<PAGE>
competitive pay practice movement. No specific performance targets were
established for fiscal year 1999, which was the base year for determining the
salary increases awarded during fiscal year 2000. In determining appropriate
levels of base salary, the Compensation Committee relied in part on several
biopharmaceutical industry compensation surveys.
 
BONUS
 
    Bonuses represent the variable component of the executive compensation
program that is tied to the Company's performance and individual achievement.
The Company's policy is to base a significant portion of its senior executives'
cash compensation on bonus. In determining bonuses, the Compensation Committee
considers factors such as relative performance of the Company during the year
and the individual's contribution to the Company's performance.
 
STOCK OPTIONS
 
    The Compensation Committee, which administers the Company's stock option
plans, believes that one important goal of the executive compensation program
should be to provide executives, key employees and consultants who have
significant responsibility for the management, growth and future success of the
Company with an opportunity to increase their ownership and potentially gain
financially from the Company's stock price increases. This approach ensures that
the best interests of the stockholders, executives and employees will be closely
aligned. Therefore, executive officers and other key employees of the Company
are granted stock options from time to time, giving them a right to purchase
shares of the Company's Common Stock at a specified price in the future. The
grant of options is based primarily on an employee's potential contribution to
the Company's growth and financial results. In determining the size of option
grants, the Compensation Committee considers the number of options owned by such
employee, the number of options previously granted and currently outstanding,
and the aggregate size of the current option grants. Options generally are
granted at the prevailing market value of the Company's Common Stock and will
only have value if the Company's stock price increases. Generally, grants of
options vest in equal amounts over four years and the individual must be
employed by the Company for such options to vest.
 
2000 COMPENSATION TO CHIEF EXECUTIVE OFFICER
 
    In reviewing and recommending Dr. Bell's salary and bonus and in awarding
him stock options for fiscal year 2000 and for his future services, the
Compensation Committee followed its compensation philosophy. Under the terms of
his employment agreement, commencing on April 1, 2000, Dr. Bell's annual salary
was increased to $332,000. For the 2000 fiscal year, Dr. Bell earned a $100,000
bonus, which was paid in August, 2000. The Compensation Committee recommended
this salary and bonus in recognition of Dr. Bell's achievements. In fiscal year
2000, Dr. Bell was granted options, to purchase 100,000 shares of the Company's
Common Stock at an exercise price of $64.50, the fair market value on the date
of grant, under the terms of the 1992 Stock Option Plan. The options will become
exercisable in equal installments over three years on the anniversary date of
the date of grant. The Compensation Committee recommended this option grant to
secure the long-term services of the Company's chief executive officer and to
further align the chief executive officer's compensation with stockholder
interests.
 
                                          COMPENSATION COMMITTEE
                                          JOHN H. FRIED, PH.D., JERRY T.
                                          JACKSON,
                                          MAX LINK, PH.D., AND ALVIN S. PARVEN
 
                                       13

<PAGE>
THE COMPANY'S STOCK PERFORMANCE
 
    The following Stock Price Performance Graph shall not be deemed incorporated
by reference by any general statement incorporating by reference this proxy
statement into any filing under the Securities Act or under the Exchange Act,
except to the extent the Company specifically incorporates this information by
reference, and shall not otherwise be deemed filed under such Acts. The
following graph compares cumulative total return of the Company's Common Stock
with the cumulative total return of (i) the Nasdaq Stock Market-United States,
and (ii) the Chase H&Q Biotechnology Index. The graph assumes (a) $100 was
invested on February 28, 1996 in each of the Company's Common Stock, the stocks
comprising the NASDAQ Stock Market-United States and the stocks comprising the
Chase H&Q Biotechnology Index, and (b) the reinvestment of dividends.
 
                            STOCK PERFORMANCE GRAPH
 
$100 INVESTED ON FEBRUARY 28, 1996 IN STOCK OR INDEX INCLUDING REINVESTMENT OF
  DIVIDENDS. FISCAL YEAR ENDING JULY 31, 2000.
 
                                    [GRAPH]

<TABLE>
<CAPTION>
                                                CUMULATIVE TOTAL RETURN
                                       -----------------------------------------
                                         3/96       7/96       1/97       7/97       1/98       7/98       1/99       7/99
                                       --------   --------   --------   --------   --------   --------   --------   --------
<S>                                    <C>        <C>        <C>        <C>        <C>        <C>        <C>        <C>
Alexion Pharmaceuticals, Inc........     100         73        147        127        161        117        164        126
Nasdaq Stock Market (U.S.)..........     100         98        125        164        148        170        231        243
Chase H&Q Biotechnology Index.......     100         89        103        161         97        108        162        200
 
<CAPTION>
 
                                        1/00       7/00       8/00
                                      --------   --------   --------
<S>                                   <C>        <C>        <C>
Alexion Pharmaceuticals, Inc........    530        782       1,273
Nasdaq Stock Market (U.S.)..........    362        347         388
Chase H&Q Biotechnology Index.......    336        314         383
</TABLE>

 
                                       14

<PAGE>
AUDIT COMMITTEE REPORT
 
    The Audit Committee of the Board of Directors reviews the financial
reporting process, the system of internal control, the audit process and the
process for monitoring compliance with laws and regulations. All of the Audit
Committee members satisfy the definition of independent director as established
in the National Association of Securities Dealers Listing Standards. The Board
of Directors adopted a written charter for the Company's Audit Committee on
September 18, 2000, which is attached to this Proxy Statement as APPENDIX A.
 
    The Audit Committee reviewed the Company's financial statements with the
Board of Directors and discussed with Arthur Andersen LLP, the Company's
independent auditors during the 2000 fiscal year, the matters required to be
discussed by Statement of Auditing Standard No. 61. The Audit Committee received
from Arthur Andersen LLP the written disclosures required by Independence
Standards Board Standard No. 1 and discussed with them their independence. After
reviewing and discussing the financial statements the Audit Committee
recommended that they be included in the Company's annual report on Form 10-K.
 
    This report of the Audit Committee shall not be deemed incorporated by
reference by any general statement incorporating by reference this Proxy
Statement into any filing under the Securities Act of 1933, as amended, or the
Securities Exchange Act of 1934, as amended, except to the extent that the
Company specifically incorporates this information by reference, and shall not
otherwise be deemed filed under such Acts.
 
                                          AUDIT COMMITTEE
                                          R. DOUGLAS NORBY
                                          JOHN H. FRIED, PH.D.
                                          MAX LINK, PH.D.
                                          LEONARD MARKS, JR., PH.D.
 
                                       15

<PAGE>
           PROPOSAL NO. 2--APPROVAL OF AN AMENDMENT TO THE 1992 STOCK
                       OPTION PLAN FOR OUTSIDE DIRECTORS
 
    The Board of Directors has unanimously adopted, subject to stockholder
approval, an amendment to the Company's 1992 Stock Option Plan for Outside
Directors to increase the formula grants provided for thereunder. The Outside
Directors' Plan was adopted by the Board of Directors in August 1992 and
approved by its stockholders in September 1992 and will terminate, unless sooner
terminated by the Board, on August 26, 2002.
 
    The Outside Directors' Plan provides for the automatic grant of options to
purchase shares of Common Stock to directors of the Company who are not
officers, employees, or consultants of the Company or any of its subsidiaries
(other than the Chairman, who shall be eligible). Subject to the provisions of
the Outside Directors' Plan, the Board has the power and authority to interpret
the Outside Directors' Plan, to prescribe, amend and rescind rules and
regulations relating to the Outside Directors' Plan and to make all other
determinations deemed necessary or advisable for the administration of the
Outside Directors' Plan. The full text of the Outside Directors' Plan and the
proposed amendments thereto are set forth in APPENDIX B to this Proxy Statement
and the following discussion is qualified by reference thereto.
 
    The Outside Directors' Plan is administered by the Compensation Committee of
the Board of Directors and provides for the issuance of "non-qualified"
incentive stock options. Options are granted under the Outside Directors' Plan
at an exercise price equal to the fair market value on the date of grant.
 
    Currently, under the Outside Directors' Plan, each Outside Director is
automatically granted an option to purchase 7,500 shares of Common Stock on the
date of his or her initial election to the Board of Directors. In addition, on
the date of the Annual Meeting and on the date of each annual meeting of
stockholders at which a director is re-elected, such director, if he or she is
still an Outside Director on such date and has attended, either in person or by
telephone, at least seventy-five percent (75%) of the meetings of the Board of
Directors that were held while he or she was a director since the prior annual
meeting of stockholders, is automatically granted an option to purchase 2,000
shares of the Company's Common Stock. All options granted under the Outside
Directors' Plan have an exercise price equal to the fair market value of the
Common Stock on the date of grant and vest in three equal annual installments
beginning on the anniversary of the date of grant.
 
    If the stockholders approve this Proposal No. 2, the initial option grant
under the Outside Directors' Plan will be increased from 7,500 shares of Common
Stock to 12,000 shares of Common Stock. The grant to Outside Directors upon
their re-election to the board will be increased from 2,000 shares of Common
Stock to 7,500 shares of Common Stock, provided such directors have attended at
least 75% of the Board meetings that were held while he or she was a director
since the prior annual meeting of stockholders.
 
FEDERAL INCOME TAX CONSEQUENCES
 
    The following summary is intended as general guidance as to the United
States federal income tax consequences under current law of participation in the
Outside Directors' Plan, and does not attempt to describe all potential tax
consequences. Tax consequences are complex and subject to change, and a
taxpayer's particular situation may be such that some variation from the
described rules is applicable. Participants should consult their own tax
advisors prior to the exercise of any options granted under the Outside
Directors' Plan or the disposition of any shares of Common Stock acquired
pursuant to the Outside Directors' Plan.
 
    An Outside Director will not recognize taxable income upon the grant of an
option. In general, the Outside Director will recognize ordinary income when the
option is exercised equal to the excess value
 
                                       16

<PAGE>
of the Common Stock with respect to which the option is exercised over the
exercise price (i.e., the option spread), and the Company will receive a
corresponding deduction in the same amount. Upon a later sale of the Common
Stock, an Outside Director will be required to recognize capital gain or loss
equal to the difference between the sale price and the value of the Common Stock
at the time the option was exercised.
 
    After reviewing and analyzing data regarding equity-based renumeration to
outside directors of similar companies in the industry, the Compensation
Committee concluded that the renumeration paid to the Outside Directors under
the Outside Directors' Plan is significantly below industry norms. Therefore,
the Board of Directors believes that approval of the amendment to increase the
grants of options to Outside Directors under the Outside Directors' Plan will
serve the best interests of the Company and its stockholders by helping the
Company attract and retain highly qualified directors who are in a position to
contribute to the successful conduct of the business and affairs of the Company
as well as stimulate in such individuals an increased desire to render greater
service to the Company.
 
VOTE REQUIRED
 
    The affirmative vote of holders of a majority of the aggregate voting power
of Common Stock issued, outstanding and entitled to vote, present or represented
at the meeting, a quorum being present, is required for the adoption of this
proposal. Broker non-votes with respect to this matter will be treated as
neither a vote "for" nor a vote "against" the matter, although they will be
counted in determining if a quorum is present. However, abstentions will be
considered in determining the number of votes required to attain a majority of
the shares present or represented at the meeting and entitled to vote.
Accordingly, an abstention from voting by a stockholder present in person or by
proxy at the meeting has the same legal effect as a vote "against" the matter
because it represents a share present or represented at the meeting and entitled
to vote, thereby increasing the number of affirmative votes required to approve
this proposal.
 
THE BOARD OF DIRECTORS DEEMS PROPOSAL NO. 2 TO BE IN THE BEST INTERESTS OF THE
COMPANY AND ITS STOCKHOLDERS AND RECOMMENDS A VOTE "FOR" APPROVAL THEREOF.
 
     PROPOSAL NO. 3--APPROVAL OF THE ADOPTION OF THE 2000 STOCK OPTION PLAN
 
    The Board of Directors has unanimously adopted the Company's 2000 Stock
Option Plan (the "2000 Plan"), subject to stockholder approval at the Annual
Meeting. The Board of Directors believes that approval of the 2000 Plan will
serve the best interests of the stockholders by permitting the Board to
establish a flexible vehicle through which it can grant options to purchase
shares of the Company's Common Stock to members of the Board of Directors and to
officers, employees, consultants and independent contractors who perform, or
will perform, services for the Company or its affiliates. There are currently
only 250,882 shares of Common Stock available for option grants under our
existing stock option plans. Therefore, the Board of Directors believes that the
approval of the adoption of the 2000 Plan is essential to allow the Company to
continue to attract and retain qualified employees, directors officers and
consultants.
 
    The primary features of the 2000 Plan are summarized below. The full text of
the 2000 Plan is set forth in APPENDIX C to this Proxy Statement and the
following discussion is qualified in its entirety by reference thereto.
 
DESCRIPTION OF THE 2000 PLAN
 
    AVAILABLE SHARES.  Subject to adjustment to reflect stock dividends and
other capital changes, the maximum number of shares of our Common Stock that may
be issued under the 2000 Plan will not exceed 1,500,000 shares and the maximum
number of shares with respect to which stock options may
 
                                       17

<PAGE>
be granted under the 2000 Plan to any employee during any calendar year will not
exceed 200,000 shares. Shares subject to options granted under the 2000 Plan
that are canceled, expired or terminated will again be available for issuance
under the 2000 Plan. Shares of Common Stock issued under the 2000 Plan may be
either authorized and unissued shares or shares held by us in our treasury. The
fair market value of our Common Stock as of October 26, 2000 was $  per share.
If the 2000 Plan is approved at the Annual Meeting, we intend to file a
registration statement on Form S-8 under the Securities Act of 1933, as amended,
to register all shares of Common Stock issuable under the 2000 Plan.
 
    ADMINISTRATION.  The 2000 Plan provides that it will be administered by a
committee of at least two directors appointed by our Board of Directors, or, if
no committee is appointed, the Board of Directors. The Compensation Committee of
the Board will be appointed to administer the 2000 Plan. Subject to the
provisions of the 2000 Plan, the Compensation Committee will have the authority
to grant options under the 2000 Plan, to interpret the provisions of the 2000
Plan, to fix and interpret the provisions of agreements governing options
granted under the 2000 Plan and to take such other actions as may be necessary
or desirable in order to carry out the provisions of the 2000 Plan.
 
    TERM OF PLAN.  The 2000 Plan will become effective on December 8, 2000,
subject to the approval of our stockholders at the Annual Meeting. The 2000 Plan
will terminate, unless terminated earlier by our Board of Directors, on
December 7, 2010.
 
    STOCK OPTION GRANTS.  Options that are intended to qualify as "incentive
stock options" within the meaning of Section 422 of the Internal Revenue Code of
1986, as amended (the "Code"), and stock options which do not so qualify, i.e.,
non-qualified options, may be granted under the 2000 Plan. Incentive stock
options may only be granted to employees of the Company or any of its
"subsidiary" corporations (within the meaning of Section 424 of the Code).
 
    The exercise price per share of a non-qualified option may not be less than
the par value of our Common Stock on the date of grant. The exercise price per
share of an incentive stock option may not be less than the fair market value of
our Common Stock on the date of grant (or, in the case of an incentive stock
option granted to an employee who owns stock possessing more than 10% of the
combined voting power of all classes of our stock or any subsidiary or parent
corporation, 110% of the fair market value).
 
    All options will, unless sooner terminated, expire not more than ten years
(or, in the case of an incentive stock option granted to a 10% stockholder, five
years) from the date of grant. The Compensation Committee will have the
discretion to determine the vesting and other restrictions on the exercise of an
option.
 
    Unless the committee determines otherwise, upon the termination of an
optionee's employment or other service with us and our affiliates, the optionee
will generally have ninety days to exercise all options that are exercisable on
the termination date, or in the event of a termination due to death or
disability, the optionee or the optionee's beneficiary, as applicable, will
generally have one year to exercise all options that are exercisable on the
termination date. If, however, an optionee is terminated by us or our affiliates
for cause (or terminates at a time when cause exists), then all options held by
the optionee will immediately terminate and cease to be exercisable.
 
    The committee has the power to cancel, rescind, suspend, withhold or
otherwise limit or restrict any outstanding option if the optionee engages in
detrimental activities. Detrimental activities include the rendering of services
to a competitor, disclosure or use of confidential information, the failure to
disclose promptly and to assign to the Company or its affiliates all right,
title and interest in any inventions or ideas, patentable or not, made or
conceived by the optionee during employment or other service with the Company or
its affiliates, or attempt to induce any employees to be employed or
 
                                       18

<PAGE>
perform services elsewhere or to solicit the trade or business of any of the
Company current or prospective customers, suppliers or partners.
 
    Payment for shares acquired upon the exercise of an option may be in cash,
certified or bank check and/or such other form of payment as may be permitted by
the Compensation Committee from time to time.
 
    NEW PLAN BENEFITS.  We do not plan to issue any predetermined stock option
grants upon the stockholders' approval of the 2000 Plan. Accordingly, we have no
information available regarding new plan benefits as we do not plan on issuing
any predetermined stock option grants to (i) any executive officer named in the
Summary Compensation Table (see "Executive Compensation"), (ii) all current
executive officers as a group, (iii) all current directors who are not executive
officers as a group and (iv) all employees, including all current officers who
are not executive officers, as a group.
 
    EXCHANGE TRANSACTIONS & CAPITAL CHANGES.  The 2000 Plan provides that in the
event of an "exchange transaction," each outstanding option will automatically
accelerate and become exercisable immediately prior to the exchange transaction
and terminate upon the occurrence of the exchange transaction, unless the
Company's stockholders receive capital stock of another company as part of the
exchange transaction and the Board of Directors directs that such options shall
be converted into options to purchase shares of the exchange stock. In general,
an "exchange transaction" is defined as a merger (other than a merger of the
Company in which the holders of Common Stock immediately prior to the merger
have the same proportionate ownership of common stock in the surviving
corporation immediately after the merger), consolidation, acquisition of
property or stock, separation, reorganization (other than a mere reincorporation
or the creation of a holding company) or liquidation of the Company, as a result
of which the stockholders of the Company receive cash, stock or other property
in exchange for or in connection with their shares of Common Stock.
 
    The number of shares available under the 2000 Plan, the maximum number of
shares with respect to stock options to be granted to any employee during any
calendar year and the number of shares subject to each outstanding option and
the exercise price thereof will be adjusted upon the occurrence of a stock split
or recapitalization of our Common Stock.
 
FEDERAL INCOME TAX CONSEQUENCES
 
    The following summary is intended only as general guidance as to the United
States federal income tax consequences under current law of participation in the
2000 Plan, and does not attempt to describe all potential tax consequences. Tax
consequences are complex and subject to change, and a taxpayer's particular
situation may be such that some variation from the described rules is
applicable. Participants should consult their own tax advisors prior to the
exercise of any options granted under the 2000 plan or the disposition of any
shares of Common Stock acquired pursuant to the 2000 Plan.
 
    In general, the holder of a non-qualified option will recognize ordinary
income upon the exercise of the option in an amount equal to the excess of the
fair market value of the shares of Common Stock with respect to which the option
is exercised at such time over the aggregate exercise price of such shares. The
Company will generally receive a corresponding tax deduction at such time. Upon
a later sale of the Common Stock, the optionee will recognize capital gain or
loss equal to the difference between the sale price and the sum of the exercise
price plus the amount of ordinary income recognized on exercise.
 
    The holder of an incentive stock option will not recognize taxable income
upon the grant or exercise of the option (although, upon exercise, the option
spread is includable as income for purposes of the alternative minimum tax). If
the Common Stock acquired upon exercise of an incentive stock option is sold or
otherwise disposed of within two years from the grant date or within one year
from the exercise date, then, in general, gain realized on the sale is treated
as ordinary income to the extent
 
                                       19

<PAGE>
of the ordinary income that would have been recognized upon exercise if the
option had been a non-qualified option, and we will generally receive a
corresponding deduction. Any remaining gain is treated as capital gain.
 
    If the Common Stock acquired pursuant to the exercise of an incentive stock
option is held for at least two years from the grant date and one year from the
exercise date and the optionee is employed by the Company (or its parents or
subsidiaries) at all times beginning on the grant date and ending on the date
three months (or, in the case of disability, one year) prior to the exercise
date, then all gain or loss realized upon the sale will be capital gain or loss
and we will not be entitled to a deduction. A special basis adjustment applies
to reduce the gain for alternative minimum tax purposes.
 
    In general, Section 162(m) of the Code denies a publicly-held corporation a
deduction for federal income tax purposes for renumeration paid in excess of
$1,000,000 per year per person to its chief executive officer and the four other
officers whose compensation is disclosed in its proxy statement, subject to
certain exceptions. Although the 2000 Plan has been designed so that
renumeration attributable to the exercise of non-qualified options granted under
the 2000 Plan will qualify for an exception from the deduction limitation, it is
possible that renumeration attributable to options granted under the 2000 Plan
will not be deductible by the Company by virtue of Section 162(m) of the Code.
 
    The 2000 Plan is not, nor is it intended to be, qualified under
Section 401(a) of the Code.
 
    VOTE REQUIRED
 
    The affirmative vote of holders of a majority of the aggregate voting power
of Common Stock issued, outstanding and entitled to vote, present or represented
at the meeting, a quorum being present, is required for the adoption of this
proposal. Broker non-votes with respect to this matter will be treated as
neither a vote "for" nor a vote "against" the matter, although they will be
counted in determining if a quorum is present. However, abstentions will be
considered in determining the number of votes required to attain a majority of
the shares present or represented at the meeting and entitled to vote.
Accordingly, an abstention from voting by a stockholder present in person or by
proxy at the meeting has the same legal effect as a vote "against" the matter
because it represents a share present or represented at the meeting and entitled
to vote, thereby increasing the number of affirmative votes required to approve
this proposal.
 
THE BOARD OF DIRECTORS DEEMS PROPOSAL NO. 3 TO BE IN THE BEST INTERESTS OF THE
COMPANY AND ITS STOCKHOLDERS AND RECOMMENDS A VOTE "FOR" APPROVAL THEREOF.
 
           PROPOSAL NO. 4--APPROVAL OF AN AMENDMENT TO THE COMPANY'S

                          CERTIFICATE OF INCORPORATION
 
    The Board of Directors has unanimously approved, subject to stockholder
approval, an amendment to Article FOURTH the Company's Certificate of
Incorporation as amended, to increase the total number of authorized shares from
30,000,000 shares to 100,000,000 shares. Of the 30,000,000 presently authorized
shares, 15,494,671 shares have been issued and were outstanding as of
October 5, 2000. In addition, an aggregate of approximately 3,830,000 shares of
Common Stock have been reserved for issuance upon conversion of outstanding
notes, warrants, options and other convertible securities.
 
    Subject to stockholder approval, Article Fourth of the Company's Certificate
of Incorporation will be amended to read as follows:
 
    "FOURTH: The total number of shares of all classes of capital stock which
    the Corporation shall have the authority to issue is 100,000,000 shares of
    which 95,000,000 shares shall be Common Stock of the par value of $0.0001
    per share and 5,000,000 shares shall be Preferred Stock of the par value of
    $0.0001 per share.
 
                                       20

<PAGE>
       A. PREFERRED STOCK.  The Board of Directors is expressly authorized to
           provide for the issue of all or any shares of the Preferred Stock, in
           one or more series, and to fix for each such series such voting
           powers, full or limited, and such designations, preferences and
           relative, participating, optional or other special rights and such
           qualifications, limitations or restrictions thereof as shall be
           stated and expressed in the resolution or resolutions adopted by the
           Board of Directors providing for the issue of such series (a
           "Preferred Stock Designation") and as may be permitted by the
           Delaware General Corporation Law. The number of authorized shares of
           Preferred Stock may be increased or decreased (but not below the
           number of shares thereof then outstanding) by the affirmative vote of
           the holders of a majority of the voting power of all of the then
           outstanding shares of the capital stock of the Corporation entitled
           to vote generally in the election of directors, voting together as a
           single class, without a separate vote of any such holders is required
           pursuant to any Preferred Stock Designation.
 
       B.  COMMON STOCK.  Except as otherwise required by law or as otherwise
           provided in any Preferred Stock Designation, the holders of the
           Common Stock shall exclusively possess all voting power and each
           share of Common Stock shall have one vote. The holders of our Common
           Stock do not possess any pre-emptive rights.
 
    The Board of Directors has proposed this increase in the authorized number
of shares of Common Stock and recommends its adoption in order to provide the
Company with greater flexibility to issue Common Stock for appropriate corporate
purposes. The purposes for which additional authorized stock could be issued
include, but are not limited to, administration of the Company's stock option
plans, funding of the Company's capital needs and corporate growth, the
acquisition of desirable businesses, the exercise of stock options granted to
attract and retain employees and for stock splits and stock dividends. If
Proposal No. 4 is not adopted, the Company will be limited in its ability to use
options as part of a compensation package, and the Company's ability to retain
existing employees and attract new employees and consultants may be adversely
affected. In addition, the Company's flexibility in raising capital and pursuing
acquisitions will be limited.
 
    The Board of Directors will determine whether, when and on what terms the
issuance of shares of Common Stock may be warranted. Like the presently
authorized but unissued shares of the Company's Common Stock, the additional
shares of Common Stock will be available without further action by the
stockholders unless such action is required by applicable law or by the rules of
the Nasdaq National Market or any applicable stock exchange. Stockholders do not
have pre-emptive rights with respect to the authorization of additional shares
of Common Stock. Except in certain cases such as a stock dividend, the issuance
of additional shares of Common Stock would have the effect of diluting the
voting powers of existing stockholders. Although the Company has filed a
registration statement on Form S-3 relating to the potential issuance of
$300,000,000 of securities which may include Common Stock, debt securities, or
warrants, the Company presently has no arrangements, commitments or
understandings with respect to the sale or issuance of any additional shares
Common Stock, except in connection with the options outstanding or to be granted
under the Company's stock option plans.
 
    Although not a factor in the Board of Directors' decision to propose the
amendment, one of the effects of the amendment to the Certificate of
Incorporation may be to enable the Board to render more difficult or to
discourage an attempt to obtain control of the Company, since the issuance of
these additional shares of Common Stock could be used to dilute the stock
ownership of persons seeking to obtain control or otherwise increase the cost of
obtaining control of the Company.
 
VOTE REQUIRED
 
    The affirmative vote of the holders of a majority of the shares of Common
Stock outstanding on October 26, 2000 is required for the adoption of the
proposed amendment to the Company's
 
                                       21

<PAGE>
Certificate of Incorporation. Broker non-votes and abstentions with respect to
this matter have the same effect as a vote "against" the matter.
 
THE BOARD OF DIRECTORS DEEMS PROPOSAL NO. 4 TO BE IN THE BEST INTERESTS OF THE
COMPANY AND ITS STOCKHOLDERS AND RECOMMENDS A VOTE "FOR" APPROVAL THEREOF.
 
           PROPOSAL NO. 5--RATIFICATION OF APPOINTMENT OF INDEPENDENT
                               PUBLIC ACCOUNTANTS
 
    The appointment of Arthur Andersen LLP as the independent public accountants
of the Company has been recommended by the Audit Committee of the Board of
Dirctors. Arthur Andersen LLP served as the independent public accountants to
audit the Company's consolidated financial statements for the fiscal year ended
July 31, 2000. Subject to stockholder approval, the Board of Directors has
appointed Arthur Andersen LLP as the Company's independent public accountants
for fiscal year 2001. Representatives of Arthur Andersen LLP are expected to
attend the fiscal year 2000 Annual Meeting. They will have an opportunity to
make a statement if they desire to do so and will be available to respond to
appropriate stockholder questions.
 
VOTE REQUIRED
 
    The affirmative vote of holders of a majority of the aggregate voting power
of Common Stock issued, outstanding and entitled to vote, present or represented
at the meeting, a quorum being present, is required for the adoption of this
proposal. Broker non-votes with respect to this matter will be treated as
neither a vote "for" nor a vote "against" the matter, although they will be
counted in determining if a quorum is present. However, abstentions will be
considered in determining the number of votes required to attain a majority of
the shares present or represented at the meeting and entitled to vote.
Accordingly, an abstention from voting by a stockholder present in person or by
proxy at the meeting has the name legal effect as a vote "against" the matter
because it represents a share present or represented at the meeting and entitled
to vote, thereby increasing the number of affirmative votes required to approve
this proposal.
 
THE BOARD OF DIRECTORS DEEMS PROPOSAL NO. 5 TO BE IN THE BEST INTERESTS OF THE
COMPANY AND ITS STOCKHOLDERS AND RECOMMENDS A VOTE "FOR" APPROVAL THEREOF.
 
                             STOCKHOLDER PROPOSALS
 
    All stockholder proposals which are intended to be presented at the 2001
annual meeting of stockholders of the Company must be received by the Company no
later than July 2, 2001 for inclusion in the Board of Directors' proxy statement
and form of proxy relating to that meeting.
 
    Stockholder proxies obtained by the Board of Directors in connection with
the 2000 annual meeting of stockholders of the Company will confer on the
proxyholders discretionary authority to vote on any matters presented at the
meeting which were not included in the proxy statement, unless notice of the
matter to be presented at the meeting is provided to our corporate secretary no
later than September 15, 2001.
 
                                 OTHER BUSINESS
 
    The Board of Directors knows of no other business to be acted upon at the
Annual Meeting. However, if any other business properly comes before the Annual
Meeting, it is the intention of the persons named in the enclosed proxy to vote
on such matters in accordance with their best judgment.
 
                                       22

<PAGE>
    The prompt return of your proxy will be appreciated and helpful in obtaining
the necessary vote. Therefore, whether or not you expect to attend the Annual
Meeting, please sign the proxy and return it in the enclosed envelope.
 
                                          By Order of the Board of Directors
 
                                          Leonard Bell, M.D.
                                          SECRETARY
 
Dated: October 30, 2000
 
A COPY OF THE COMPANY'S ANNUAL REPORT ON FORM 10K WILL BE SENT WITHOUT CHARGE TO
ANY STOCKHOLDER REQUESTING IT IN WRITING FROM: ALEXION PHARMACEUTICALS, INC., 25
SCIENCE PARK, NEW HAVEN, CONNECTICUT 06511, ATTENTION: PRESIDENT.
 
                                       23

<PAGE>

                                                                      APPENDIX A
 
                         ALEXION PHARMACEUTICALS, INC.
                            AUDIT COMMITTEE CHARTER
 
I.  COMPOSITION
 
    The Audit Committee (the "Committee") of Alexion Pharmaceuticals, Inc. (the
"Company") is a standing committee of the Board of Directors (the "Board")
established to assist the Board in fulfilling its statutory, regulatory and
fiduciary responsibilities. The Committee shall consist of at least three
"independent" directors who shall meet the "membership requirements" of Nasdaq
(as both those terms are defined by Nasdaq). At least one of the directors on
the Committee shall have past employment experience in finance or accounting,
the requisite professional certification in accounting or other comparable
experience or background required by Nasdaq, as the same may be amended from
time to time. The Board shall appoint the members of the Committee.
 
II.  AUTHORITY
 
    The Committee shall have the authority to retain special legal, accounting
or other consultants to advise the Committee. The Committee may request any
officer or employee of the Company or the Company's outside counsel or
independent public accountants to attend a meeting of the Committee or to meet
with any members of, or consultants to, the Committee.
 
III.  PURPOSE
 
    The purpose of the Committee shall be to assist the Board in fulfilling its
oversight responsibilities. The Committee will review the financial reporting
process, systems of internal control, the audit process and the Company's
process for monitoring compliance with the laws, regulations and the Company's
code of conduct. In performing its duties, the Committee will maintain effective
working relationships with the Board, management, and the internal and external
auditors.
 
IV.  MEETINGS
 
    The Committee will have at least one scheduled meeting each fiscal year. In
addition, the Committee will meet at other times if deemed necessary to
completely discharge its duties and responsibilities as outlined in this
charter. As part of its job to foster open communication, the Committee should
meet at least annually with management, the internal auditors and the
independent public accountants, in separate executive sessions, to discuss any
matters that the Committee or each of these groups believe should be discussed
privately.
 
V.  RESPONSIBILITIES AND DUTIES
 
    The Board delegates to the Committee the following specific duties and
responsibilities in addition to those in the preceding paragraphs:
 
    DOCUMENTS/REPORTS REVIEW
 
    1.  Review and reassess the adequacy of the Audit Committee Charter annually
       and submit the Charter to the Board for approval.
 
    2.  Review the Company's annual audited financial statements and any reports
       or other financial information as the Committee may request, including,
       without limitation, any material submitted to any governmental body, or
       the public, including any certification, report, opinion or review
       rendered by the independent public accountants. Discuss major issues and
       significant changes regarding accounting and auditing principles and
       practices as well as the adequacy of internal controls that could
       significantly affect the Company's financial statements.

<PAGE>
    3.  Review any reports to management prepared by the internal auditing
       department, together with management's response. Review with management
       and the independent public accountants significant financial reporting
       issues and judgments made in connection with the preparation of the
       Company's financial statements.
 
    4.  Review with management and the independent public accountants the
       Company's annual report on Form 10-K and the Company's quarterly report
       on Form10-Q prior to its filing or prior to the release of earnings. The
       chair of the Committee may represent the entire Committee for purposes of
       these reviews.
 
    5.  Review the Company's major financial risk exposures and the steps
       management has taken to monitor and control such exposures.
 
    INDEPENDENT PUBLIC ACCOUNTANTS
 
    1.  Recommend to the Board the selection, or dismissal when appropriate, of
       the independent public accountants, which firm is ultimately accountable
       to the Board. Consider independence and effectiveness and approve the
       fees and other compensation to be paid to the independent public
       accountants. On an annual basis, the Committee should review and discuss
       with the accountants all significant relationships the accountants have
       with the Company to confirm the accountants' independence.
 
    2.  Meet with the independent public accountants to review the scope,
       accuracy, completeness and overall quality of the annual financial
       statements.
 
    3.  Receive from the independent public accountants the information they are
       required to communicate to the Committee under generally accepted
       auditing standards, including, without limitation:
 
       a.  A formal written statement delineating all relationships between the
           independent public accountants and the Company, consistent with
           Independence Standards Board Standard No. 1, and
 
       b.  Engage in a dialogue with the independent public accountants with
           respect to any disclosed relationships or services that may impact
           the objectivity and independence of the independent public
           accountants, and recommend that the Board take appropriate action to
           enhance the independence of the independent public accountants.
 
    FINANCIAL REPORTING PROCESS
 
    1.  In consultation with the independent public accountants, review the
       integrity of the Company's financial reporting processes, both internal
       and external.
 
    2.  Meet with management and the independent public accountants to review
       the planning and staffing of the audit.
 
    3.  Discuss with the independent public accountants the matters required to
       be discussed by Statement on Auditing Standards No. 61, as modified or
       amended, relating to the conduct of the audit.
 
    4.  Review with the independent public accountants any problems or
       difficulties the accountants may have encountered and any management
       letter provided by the accountants and the Company's response to that
       letter. Such review should include:
 
       a.  Any difficulties encountered in the course of the audit work,
           including any restrictions on the scope of activities or access to
           required information.
 
       b.  Any changes required in the planned scope of the audit.
 
    5.  The Committee shall make regular reports to the Board of Directors. The
       Committee shall also prepare the report required by the rules of the
       Securities and Exchange Commission to be included in the Company's annual
       proxy statement.

<PAGE>
VI.  OTHER
 
    While the Committee has the responsibility and powers set forth in this
Charter, it is not the duty of the Committee to plan or conduct audits or to
determine that the Company's financial statements are complete and accurate and
are in accordance with generally accepted accounting principles. This is the
responsibility of management and the independent public accountants. Nor is it
the duty of the Committee to conduct investigations, unless authorized by the
Board of Directors, to resolve disagreements, if any, between management and the
independent public accountants, or to assure compliance with laws and
regulations.

<PAGE>
                                                                      APPENDIX B
 
    BELOW IS THE TEXT OF THE COMPANY'S 1992 STOCK OPTION PLAN FOR OUTSIDE
DIRECTORS AS PROPOSED TO BE AMENDED PURSUANT TO PROPOSAL NO. 2. PROPOSED
LANGUAGE TO THE 1992 STOCK OPTION PLAN FOR OUTSIDE DIRECTORS IS SET FORTH IN
BOLD AND THE LANGUAGE TO BE DELETED IS SET FORTH IN BRACKETS.
 
                         ALEXION PHARMACEUTICALS, INC.
                  1992 STOCK OPTION PLAN FOR OUTSIDE DIRECTORS
 
I  PURPOSE.
 
    The purpose of this 1992 Stock Option Plan for Outside Directors (the
"Plan") of Alexion Pharmaceuticals, Inc. (the "Corporation") is to enable the
Corporation to compensate eligible directors of the Corporation and to encourage
the highest level of performance by providing such persons with a proprietary
interest in the Corporation's success and progress by granting them shares of
the Corporation's Common Stock, par value $.0001 per share ("Common Stock").
 
II  ADMINISTRATION OF THE PLAN
 
    The Plan shall be administered by a committee (the "Committee") of the Board
of Directors of the Corporation (the "Board"), which shall consist of one or
more members of the Board, appointed by the Board, who are outside directors (as
defined below) or by the Board. The interpretation and construction by the
Committee of any provisions of the Plan or of any other matters related to the
Plan shall be final. The Committee may from time to time adopt such rules and
regulations for carrying out the Plan as it may deem advisable. No member of the
Board or the Committee shall be liable for any action or determination made in
good faith with respect to the Plan. The Plan shall be interpreted and
implemented such that the eligible outside directors will not fail, by reason of
the Plan or its implementation, to be "disinterested persons" within the meaning
of Rule 16b-3 of the Securities Exchange Act of 1934 (the "Exchange Act"), as
such Rule and such Act may be amended.
 
III  ELIGIBILITY AND ISSUANCES.
 
    A. ELIGIBILITY. Directors of the Corporation who (i) are neither officers
nor employees nor consultants of the Corporation or any of its subsidiaries
(other than the Chairman of the Board of Directors of the Corporation who shall
be eligible) and (ii) are not affiliated with any person referred to in
(i) above ("outside directors") shall be eligible to receive options to purchase
Common Stock under the Plan.
 
    B. ISSUANCES
 
    (1) Except as set forth in Section 3(b)(ii) below, each outside director
shall be issued an option to purchase [7,500] 12,000 shares of the Corporation's
Common Stock (the "Initial Option") on the date of his initial election or
appointment to the Board of Directors (the "Initial Grant Date") on the
following terms:
 
        (a) The option exercise price per share of Common Stock shall be the
    Fair Market Value (as defined below) of the Common Stock covered by such
    Initial Option on the Initial Grant Date.
 
        (b) Except as provided herein, the term of an Initial Option shall be
    for a period of ten (10) years from the Initial Grant Date.
 
    (2) In the case of Drs. John A. Fried, Max Link and Leonard Marks, Jr.,
outside directors who were elected as directors of the Corporation in
April 1992, Initial Options to purchase 7,500 (after giving effect to a 1 for 4
reverse stock split effected on November 7, 1994 and a 1 for 2.5 reverse stock
split effected on January 5, 1996) shares of the Corporation's Common Stock were
granted under the Plan on August 27, 1992, the date of the Plan's adoption by
the Board.

<PAGE>
    (3) In addition, each outside director shall, on the date of each annual
meeting of stockholders at which he is reelected as a director (the "Additional
Grant Date"), if he is still an outside director on such date and has attended,
either in person or by telephone, at least seventy-five percent (75%) of the
meetings of the Board of Directors that were held while he was a director since
the prior annual meeting of stockholders, be granted an option to purchase
[2,000] 7,500 shares of Common Stock (the "Additional Option" and, together with
the Initial Option, an "Option") on the following terms:
 
        (a) The option exercise price per share of Common Stock shall be the
    Fair Market Value (as defined below) of the Common Stock covered by such
    Additional Option on the Additional Grant Date.
 
        (b) Except as provided herein, the term of an Additional Option shall be
    for a period of ten (10) years from the Additional Grant Date.
 
    (4) "Fair Market Value" shall mean, for each Initial Grant Date or
Additional Grant Date (collectively, a "Grant Date"), (A) if the Common Stock is
listed or admitted to trading on the New York Stock Exchange (the "NYSE") or the
American Stock Exchange (the "ASE"), the last reported sale price of the Common
Stock on such date or, if no sale takes place on such date, the closing asked
prices of the Common Stock on such exchange as of such date, in each case as
officially reported on the NYSE or the ASE, or (B) if no shares of Common Stock
are then listed or admitted to trading on the NYSE or the ASE, the last reported
sales price of the Common Stock on such date on the NASDAQ National Market
System ("NASDAQ") or, if no shares of Common Stock are then quoted on NASDAQ,
the average of the closing bid and the highest asked prices of the Common Stock
on such date on NASDAQ, or, if no shares of Common Stock are then quoted on
NASDAQ, the average of the highest bid and the lowest asked prices of the Common
Stock on such date as reported on the over-the-counter system. If no closing bid
and lowest asked prices thereof are then so quoted or published in the
over-the-counter market, "Fair Market Value" shall mean the fair value per share
of Common Stock (assuming for the purposes of this calculation the economic
equivalence of all shares of classes of capital stock), as determined on a fully
diluted basis in good faith by the Board, as of a date which is 15 days
preceding the Grant Date; PROVIDED, HOWEVER, that the Fair Market Value of the
Common Stock for purposes of Options granted prior to the closing of the
Corporation's initial private placement of Common Stock or initial public
offering, whichever occurs earliest, shall be the price per share of the Common
Stock in such private placement or public offering.
 
    (5) Options granted hereunder shall not be "incentive stock options" within
the meaning of Section 422A of the Internal Revenue Code of 1986, as amended.
 
IV  REGULATORY COMPLIANCE AND LISTING.
 
    The issuance or delivery of any Option may be postponed by the Corporation,
and an Option shall not be exercisable, for such period as may be required to
comply with the Federal securities laws, state "blue sky" laws, any applicable
listing requirements of any applicable securities exchange and any other law or
regulation applicable to the issuance, delivery or exercise of such Options and
the Corporation shall not be obligated to issue or deliver any Options or shares
of Common Stock if the issuance or delivery of such Options or shares would
constitute a violation of any law or any regulation of any governmental
authority or applicable securities exchange.
 
V  RESTRICTIONS ON EXERCISABILITY.
 
    A. Except as provided in Section 5(b) below, each Option granted under the
Plan may be exercisable as to one-third of the total number of shares issuable
under such Option on each of the three successive anniversaries of the Grant
Date of such Option.
 
    B. If any event constituting a "Change in Control of the Corporation" shall
occur, all Options granted under the Plan, which are outstanding at the time a
Change of Control of the Corporation shall occur, shall immediately become
exercisable. A "Change in Control of the Corporation" shall be deemed to occur
if (i) there shall be consummated (x) any consolidation or merger of the
Corporation

<PAGE>
in which the Corporation is not the continuing or surviving corporation or
pursuant to which shares of the Corporation's Common Stock would be converted
into cash, securities or other property, other than a merger of the Corporation
in which the holders of the Corporation's Common Stock immediately prior to the
merger have the same proportionate ownership of common stock of the surviving
corporation immediately after the merger, or (y) any sale, lease, exchange or
other transfer (in one transaction or a series of related transactions) of all,
or substantially all, of the assets of the Corporation, or (ii) the stockholders
of the Corporation shall approve any plan or proposal for liquidation or
dissolution of the Corporation, or (iii) any person (as such term is used in
Section 13(d) and 14(d)(2) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act")), shall become the beneficial owner (within the meaning of
Rule 13d-3 under the Exchange Act) of 40% or more of the Corporation's
outstanding Common Stock other than pursuant to a plan or arrangement entered
into by such person and the Corporation, or (iv) during any period of two
consecutive years, individuals who at the beginning of such period constitute
the entire Board shall cease for any reason to constitute a majority thereof
unless the election, or the nomination for election by the Corporation's
stockholders, of each new director was approved by a vote of at least two-thirds
of the directors then still in office who were directors at the beginning of the
period.
 
VI  CESSATION AS DIRECTOR.
 
    In the event that the holder of an Option granted pursuant to the Plan shall
cease to be a director of the Corporation for any reason, such holder may
exercise any portion of such Option that is exercisable by him at the time he
ceases to be a director of the Corporation, but only to the extent such Option
is exercisable as of such date, within six months after the date he ceases to be
a director of the Corporation.
 
VII  DEATH.
 
    In the event that a holder of an Option granted pursuant to the Plan shall
die, his beneficiary may exercise any portion of such Option that was
exercisable by the deceased Optionee at the time of his death, but only to the
extent such Option is exercisable as of such date, within twelve months after
the date of his death.
 
VIII  STOCK SPLITS, MERGERS, ETC.
 
    In the event of any stock split, stock dividend or similar transaction which
increases or decreases the number of outstanding shares of Common Stock,
appropriate adjustment shall be made by the Board, whose determination shall be
final, to the number and option exercise price per share of Common Stock which
may be purchased under any outstanding Options. In the case of a merger,
consolidation or similar transaction which results in a replacement of the
Corporation's Common Stock and stock of another corporation but does not
constitute a Change in Control of the Corporation, the Corporation will make a
reasonable effort, but shall not be required, to replace any outstanding Options
granted under the Plan with comparable options to purchase the stock of such
other corporation, or will provide for immediate maturity of all outstanding
Options, with all Options not being exercised within the time period specified
by the Board of Directors being terminated.
 
IX  TRANSFERABILITY.
 
    Options are not assignable or transferable, except by will or the laws of
descent and distribution to the extent set forth in Section 7 and during a
director's lifetime may be exercised only by him. Notwithstanding the preceding
sentence, the Committee may, in its sole discretion, permit an optionee to
transfer an Option granted pursuant to the Plan, in whole or in part, to such
persons and/or entities as are approved by the Committee from time to time and
subject to such terms and conditions as the Committee may determine from time to
time, including, without limitation, such terms and conditions as are necessary
or desirable to comply with applicable law.

<PAGE>
X  EXERCISE OF OPTIONS.
 
    An optionholder electing to exercise an Option shall give written notice to
the Corporation of such election and of the number of shares of Common Stock
that he has elected to acquire. An optionholder shall have no rights of a
stockholder with respect to shares of Common Stock covered by his Option until
after the date of issuance of a stock certificate to him upon partial or
complete exercise of his option.
 
XI  PAYMENT.
 
    The Option exercise price shall be payable in cash, check or in shares of
Common Stock upon the exercise of the Option. If the shares of Common Stock are
tendered as payment of the Option exercise price, the value of such shares shall
be the Fair Market Value as of the date of exercise. If such tender would result
in the issuance of fractional shares of Common Stock, the Corporation shall
instead return the difference in cash or by check to the employee.
 
XII  TERM OF PLAN.
 
    The Plan shall terminate on August 26, 2002, and no Option shall be granted
pursuant to the Plan after that date.
 
XIII  OBLIGATION TO EXERCISE OPTION.
 
    The granting of an Option shall impose no obligation on the director to
exercise such Option.
 
XIV  CONTINUANCE AS DIRECTOR.
 
    Nothing in the Plan shall be deemed to create any obligation on the part of
the Board to nominate any director for reelection by the Corporation's
stockholders.
 
XV  AMENDMENT OF THE PLAN.
 
    The Board may at any time and from time to time alter, amend, suspend or
terminate the Plan in whole or in part, provided, however, that (i) any
amendment which must be approved by the stockholders of the Company in order to
maintain the continued qualification of the Plan under Rule 16b-3 under the
Exchange Act or any successor provision, or the approval of which is otherwise
required by law, shall not be effective unless and until such stockholder
approval has been obtained in compliance with such rule or law and
(ii) provisions of the Plan which govern the amount, price or timing of the
award of an Option shall not be amended more than once every six months, other
than to comply with changes in the Internal Revenue Code of 1986, as amended,
the Employee Income Retirement Security Act, or the rules thereunder.
 
XVI  WITHHOLDING OF TAXES.
 
    We shall have the right, prior to the delivery of any certificate evidencing
shares of Common Stock to be issued pursuant to an Option, to require the
exercising outside director to remit to the Company an amount in cash sufficient
to satisfy any Federal, state, or local tax withholding requirements.

<PAGE>
                                                                      APPENDIX C
 
                         ALEXION PHARMACEUTICALS, INC.
                             2000 STOCK OPTION PLAN
 
    1.  PURPOSE. The purpose of the Alexion Pharmaceuticals, Inc. 2000 Stock
Option Plan (the "Plan") is to establish a vehicle through which Alexion
Pharmaceuticals, Inc. (the "Company") can make discretionary grants of Options
to purchase shares of the Company's common stock, par value $0.0001 (the "Common
Stock") to members of the Board of Directors of the Company (the "Board"), to
officers and other employees of the Company and its Affiliates and to
consultants and other independent contractors of the Company and its Affiliates,
with a view toward promoting the long-term financial success of the Company and
enhancing stockholder value.
 
    2.  DEFINITIONS. For purposes of the Plan, the following terms shall have
the following meanings:
 
        (a) "AFFILIATE" shall mean an affiliate within the meaning of
    Rule 12b-2 under the Exchange Act.
 
        (b) "CAUSE" shall mean, unless otherwise determined by the Committee:
    (1) in the case where there is no employment or consulting agreement between
    the optionee and the Company or its Affiliates at the time of grant or where
    such an agreement exists but does not define "cause" (or words of like
    import), the optionee's dishonesty, fraud, insubordination, willful
    misconduct, refusal to perform services, unsatisfactory performance of
    services or material breach of any written agreement between the optionee
    and the Company or its Affiliates, or (2) in the case where there is an
    employment or consulting agreement between the optionee and the Company or
    its Affiliates at the time of grant which defines "cause" (or words of like
    import), the meaning ascribed to such term under such agreement.
 
        (c) "CHANGE IN CONTROL" shall be deemed to occur if: (1) there shall be
    consummated (x) any consolidation or merger of the Company in which the
    Company is not the continuing or surviving corporation or pursuant to which
    shares of Common Stock would be converted into cash, securities or other
    property, other than a merger of the Company in which the holders of the
    Common Stock immediately prior to the merger have the same proportionate
    ownership of common stock of the surviving corporation immediately after the
    merger, or (y) any sale, lease, exchange or other transfer (in one
    transaction or a series of related transactions) of all, or substantially
    all, of the assets of the Company, (2) the stockholders of the Company shall
    approve any plan or proposal for liquidation or dissolution of the Company,
    or (3) any person (as such term is used in Section 13(d) and 14(d)(2) of the
    Exchange Act), shall become the beneficial owner (within the meaning of
    Rule 13d-3 under the Exchange Act) of forty percent (40%) or more of the
    outstanding Common Stock, or (4) during any period of two (2) consecutive
    years, individuals who at the beginning of such period constitute the entire
    Board shall cease for any reason to constitute a majority thereof unless the
    election, or the nomination for election by the Company's stockholders, of
    each new director was approved by a vote of at least two-thirds of the
    directors then still in office who were directors at the beginning of the
    period or were so approved.
 
        (d) "CODE" shall mean the Internal Revenue Code of 1986, as amended.
 
        (e) "COMMITTEE" shall mean the committee, consisting of at least two
    (2) directors, appointed by the Board from time to time to administer the
    Plan or, if no such committee is appointed, the Board.
 
        (f) "DETRIMENTAL ACTIVITY" shall mean: (1) the rendering of services for
    any organization or engaging directly or indirectly in any business which is
    or becomes competitive with the Company or its Affiliates, or which
    organization or business, or the rendering of services to such organization
    or business, is or becomes otherwise prejudicial to or in conflict with the
    interests of the Company or its Affiliates, (2) the disclosure to anyone
    outside the Company or its Affiliates, or the use in other than the
    Company's or its Affiliates' business, without prior written

<PAGE>
    authorization from the Company, of any confidential information or material
    relating to the business of the Company or its Affiliates, acquired by the
    optionee either during or after employment or other service with the Company
    or its Affiliates, (3) the failure or refusal to disclose promptly and to
    assign to the Company or its Affiliates all right, title and interest in any
    invention or idea, patentable or not, made or conceived by the optionee
    during employment by or other service with the Company or its Affiliates,
    relating in any manner to the actual or anticipated business, research or
    development work of the Company or its Affiliates or the failure or refusal
    to do anything reasonably necessary to enable the Company or its Affiliates
    to secure a patent where appropriate in the United States and in other
    countries, or (4) any attempt directly or indirectly to induce any employee
    of the Company or its Affiliates to be employed or perform services
    elsewhere or any attempt directly or indirectly to solicit the trade or
    business of any current or prospective customer, supplier or partner of the
    Company or its Affiliates.
 
        (g) "DISABILITY" shall mean, unless as otherwise determined by the
    Committee or as provided in an employment agreement, the inability of an
    optionee to perform the customary duties of his or her employment or other
    service for the Company or its Affiliates by reason of a physical or mental
    incapacity which is expected to result in death or to be of indefinite
    duration.
 
        (h) "EFFECTIVE DATE" shall mean the date on which the Plan was adopted
    by the Board, subject to the approval of the Company's stockholders within
    twelve (12) months of such date.
 
        (i) "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
    amended.
 
        (j) "EXCHANGE TRANSACTION" shall mean a merger (other than a merger of
    the Company in which the holders of Common Stock immediately prior to the
    merger have the same proportionate ownership of Common Stock in the
    surviving corporation immediately after the merger), consolidation,
    acquisition of property or stock, separation, reorganization (other than a
    mere reincorporation or the creation of a holding company) or liquidation of
    the Company, as a result of which the stockholders of the Company receive
    cash, stock or other property in exchange for or in connection with their
    shares of Common Stock.
 
        (k) "FAIR MARKET VALUE" as of any date shall mean, unless otherwise
    required by the Code or other applicable law, the closing sale price per
    share of Common Stock as published by the principal national securities
    exchange on which the Common Stock is traded on such date or, if there is no
    sale of Common Stock on such date, the average of the bid and asked prices
    on such exchange at the close of trading on such date, or if shares of the
    Common Stock are not listed on a national securities exchange on such date,
    the closing price or, if none, the average of the bid and asked prices in
    the over-the-counter market at the close of trading on such date, or if the
    Common Stock is not traded on a national securities exchange or the
    over-the-counter market, the value of a share of the Common Stock on such
    date as determined in good-faith by the Committee.
 
        (l) "INCENTIVE STOCK OPTION" shall mean an Option that is intended to be
    an "incentive stock option" within the meaning of Section 422 of the Code.
 
        (m) "NON-QUALIFIED STOCK OPTION" shall mean an Option that is not an
    Incentive Stock Option.
 
        (n) "OPTION" shall mean an Incentive Stock Option or a Non-Qualified
    Stock Option granted pursuant to the Plan.
 
        (o) "SECURITIES ACT" shall mean the Securities Act of 1933, as amended.
 
        (p) "SUBSIDIARY" shall mean any "subsidiary corporation" of the Company
    within the meaning of Section 424(f) of the Code.
 
        (q) "TEN PERCENT STOCKHOLDER" shall mean a person owning, at the time of
    grant, stock possessing more than ten percent (10%) of the total combined
    voting power of all classes of stock

<PAGE>
    of the Company or any parent or subsidiary corporation within the meaning of
    Section 424 of the Code.
 
3.  ADMINISTRATION.
 
        (a) COMMITTEE. The Plan shall be administered and interpreted by the
    Committee.
 
        (b) AUTHORITY OF COMMITTEE. Subject to the limitations of the Plan, the
    Committee, acting in its sole and absolute discretion, shall have full power
    and authority to: (1) select the persons to whom Options shall be granted,
    (2) grant Options to such persons and prescribe the terms and conditions of
    such Options (including, but not limited to, the exercise and vesting
    conditions applicable thereto), (3) interpret and apply the provisions of
    the Plan and of any agreement or other instrument evidencing an Option,
    (4) carry out any responsibility or duty specifically reserved to the
    Committee under the Plan, and (5) make any and all determinations and
    interpretations and take such other actions as may be necessary or desirable
    in order to carry out the provisions, intent and purposes of the Plan. A
    majority of the members of the Committee shall constitute a quorum. The
    Committee may act by the vote of a majority of its members present at a
    meeting at which there is a quorum or by unanimous written consent. The
    determinations of the Committee, including with regard to questions of
    construction, interpretation and administration, shall be final, binding and
    conclusive on all persons.
 
        (c) INDEMNIFICATION. The Company shall indemnify and hold harmless each
    member of the Committee and the Board and any employee of the Company who
    provides assistance with the administration of the Plan from and against any
    loss, cost, liability (including any sum paid in settlement of a claim with
    the approval of the Board), damage and expense (including the advancement of
    reasonable legal and other expenses incident thereto) arising out of or
    incurred in connection with the Plan, unless and except to the extent
    attributable to such person's fraud or willful misconduct.
 
    4.  ELIGIBILITY. Options may be granted under the Plan to any member of the
Board (whether or not an employee of the Company or its Affiliates), to any
officer or other employee of the Company or its Affiliates and to any consultant
or other independent contractor who performs or will perform services for the
Company or its Affiliates. Notwithstanding the foregoing, Incentive Stock
Options may only be granted to persons who are employed by the Company or a
Subsidiary at the time of grant.
 
    5.  AVAILABLE SHARES. Subject to adjustment as provided in Section 10,
(a) the maximum number of shares of Common Stock that may be issued under the
Plan shall not exceed 1,500,000 shares, and the (b) maximum number of shares of
Common Stock with respect to which Options may be granted to any employee of the
Company or its Affiliates in any calendar year shall not cover more than 200,000
shares. Shares of Common Stock available for issuance under the Plan may be
either authorized and unissued or held by the Company in its treasury. New
Options may be granted under the Plan with respect to Shares of Common Stock
which are covered by the unexercised portion of an Option which has terminated
or expired by its terms, by cancellation or otherwise. No fractional shares of
Common Stock may be issued under the Plan.
 
    6.  DISCRETIONARY STOCK OPTIONS.
 
        (a) TYPE OF OPTIONS. Subject to the provisions hereof, the Committee may
    grant Incentive Stock Options and Non-Qualified Stock Options to eligible
    personnel upon such terms and conditions as the Committee deems appropriate.
 
        (b) OPTION TERM. Unless sooner terminated, all Options shall expire not
    more than ten (10) years after the date the Option is granted (or, in the
    case of an Incentive Stock Option granted to a Ten Percent Stockholder, not
    more than five (5) years).
 
        (c) EXERCISE PRICE. The exercise price per share of Common Stock covered
    by a Non-Qualified Stock Option may not be less than the par value of a
    share of Common Stock on the date the Option is granted. The exercise price
    per share of Common Stock covered by an Incentive Stock Option may not be
    less than one hundred percent (100%) of the Fair Market Value of a share of

<PAGE>
    Common Stock on the date the Option is granted one hundred ten percent
    (110%) in case of an optionee who is a Ten Percent Stockholder).
 
        (d) EXERCISE OF OPTIONS. The Committee may establish such vesting and
    other conditions and restrictions on the exercise of an Option and/or upon
    the issuance of Common Stock in connection with the exercise of an Option as
    it deems appropriate. All or part of the exercisable portion of an Option
    may be exercised at any time during the Option term, except that, without
    the consent of the Committee, no partial exercise of an option may be for
    less than one hundred (100) shares.
 
        (e) PAYMENT OF EXERCISE PRICE. An Option may be exercised by
    transmitting to the Company: (i) a written notice specifying the number of
    shares to be purchased, and (ii) payment of the exercise price, together
    with the amount, if any, deemed necessary by the Committee to enable the
    Company to satisfy its federal, state, foreign or other tax withholding
    obligations with respect to such exercise. The Committee may establish such
    rules and procedures as it deems appropriate for the exercise of Options.
    The exercise price of shares of Common Stock acquired pursuant to the
    exercise of an Option may be paid in cash, certified or bank check and/or
    such other form of payment as may be permitted by the Committee from time to
    time, including, without limitation, shares of Common Stock which have been
    owned by the holder for at least six (6) months (free and clear of any liens
    and encumbrances).
 
    7.  NON-TRANSFERABILITY. No Option shall be transferable by an optionee
other than upon the optionee's death to a beneficiary designated by the
optionee, or, if no designated beneficiary shall survive the optionee, pursuant
to the optionee's will or by the laws of descent and distribution. All Options
shall be exercisable during an optionee's lifetime only by the optionee. Any
attempt to transfer any Option shall be void, and no such Option shall in any
manner be liable for or subject to the debts, contracts, liabilities,
engagements or torts of any person who shall be entitled to such Option, nor
shall it be subject to attachment or legal process for or against such person.
Notwithstanding the foregoing, the Committee may, in its sole discretion, permit
an optionee to transfer a Non-Qualified Stock Option, in whole or in part, to
such persons and/or entities as are approved by the Committee from time to time
and subject to such terms and conditions as the Committee may determine from
time to time, including, without limitation, such terms and conditions as are
necessary or desirable to comply with applicable law.
 
    8.  EFFECT OF TERMINATION OF EMPLOYMENT OR OTHER SERVICE. Except as
otherwise provided herein or determined by the Committee, the following rules
shall apply with regard to Options held by an optionee at the time of his or her
termination of employment or other service with the Company and its Affiliates:
 
        (a) TERMINATION DUE TO DEATH OR DISABILITY. If an optionee's employment
    or other service terminates due to his or her death or Disability (or if the
    optionee's employment or other service is terminated by reason of his or her
    Disability and the optionee dies within one year of such termination of
    employment or other service), then: (i) that portion of an Option that is
    not exercisable on the date of termination shall immediately terminate, and
    (ii) that portion of an Option that is exercisable on the date of
    termination shall remain exercisable, to the extent exercisable on the date
    of termination, by the optionee (or the optionee's designated beneficiary or
    representative) during the one year period following the date of termination
    (or, during the one year after the later death of a disabled optionee) or,
    if sooner, until the expiration of the stated term thereof, and, to the
    extent not exercised during such period, shall thereupon terminate.
 
        (b) TERMINATION FOR CAUSE OR AT A TIME WHEN CAUSE EXISTS. If an
    optionee's employment or other service is terminated by the Company or an
    Affiliate for Cause or if, at the time of his or her termination, grounds
    for a termination for Cause exist, then any Option held by the optionee
    (whether or not then exercisable) shall immediately terminate and cease to
    be exercisable.
 
        (c) OTHER TERMINATION. If an optionee's employment or other service
    terminates for any reason or no reason, then, except as provided for in an
    employment agreement: (i) that portion of an Option held by the optionee
    that is not exercisable on the date of termination shall immediately

<PAGE>
    terminate, and (ii) that portion of an Option that is exercisable on the
    date of termination shall remain exercisable, to the extent exercisable on
    the date of termination, by the optionee during the ninety (90) day period
    following the date of termination or, if sooner, until the expiration of the
    stated term thereof, and, to the extent not exercised during such period,
    shall thereupon terminate.
 
    9.  CANCELLATION AND RESCISSION OF OPTIONS. Unless an Option agreement
specifies otherwise, the Committee may cancel, rescind, suspend, withhold or
otherwise limit or restrict any unexpired Option at any time if the optionee is
not in compliance with all applicable provisions of the award agreement and the
Plan, or if the optionee engages in a Detrimental Activity. Upon exercise of an
Option, the optionee shall certify in a manner acceptable to the Company that he
or she is in compliance with the terms and conditions of the Plan and has not
engaged in any Detrimental Activities. In the event an optionee engages in any
Detrimental Activity prior to, or during the six (6) months after, any exercise,
such exercise may be rescinded within two (2) years thereafter. In the event of
any such rescission, the optionee shall pay to the Company the amount of any
gain realized as a result of the rescinded exercise, in such manner and on such
terms and conditions as may be required, and the Company and its Affiliates
shall be entitled to set-off against the amount of any such gain, any amount
owed to the optionee by the Company or its Affiliates.
 
    10. CAPITAL CHANGES; REORGANIZATION; SALE.
 
        (a) ADJUSTMENTS UPON CHANGES IN CAPITALIZATION. The aggregate number and
    class of shares which may be issued under the Plan, the maximum number and
    class of shares with respect to which an Option may be granted to any
    employee during any calendar year and the number and class of shares and the
    exercise price per share in effect under each outstanding Option shall all
    be adjusted proportionately for any increase or decrease in the number of
    issued shares of Common Stock resulting from a split-up or consolidation of
    shares or any like capital adjustment, or the payment of any stock dividend.
 
        (b) CASH, STOCK OR OTHER PROPERTY FOR STOCK. Except as otherwise
    provided in this subparagraph, in the event of an Exchange Transaction, all
    optionees shall be permitted to exercise their outstanding Options (whether
    or not otherwise exercisable) at least fifteen (15) days prior to the
    Exchange Transaction (and the Board shall notify each optionee of such
    acceleration at least fifteen (15) days prior to the Exchange Transaction)
    and any outstanding Options not exercised before the consummation of the
    Exchange Transaction shall thereupon terminate. Notwithstanding the
    preceding sentence, if, as a part of the Exchange Transaction, the
    stockholders of the Company receive capital stock of another corporation
    ("Exchange Stock"), and if the Board, in its sole discretion, so directs,
    then all outstanding Options shall be converted into Options to purchase
    shares of Exchange Stock. The amount and price of the converted options
    shall be determined by adjusting the amount and price of the Options granted
    hereunder on the same basis as the determination of the number of shares of
    Exchange Stock the holders of Common Stock shall receive in the Exchange
    Transaction.
 
        (c) FRACTIONAL SHARES. In the event of any adjustment in the number of
    shares covered by an Option, any fractional shares resulting from such
    adjustment shall be disregarded, and each such Option shall cover only the
    number of full shares resulting from the adjustment.
 
        (d) DETERMINATION OF BOARD TO BE FINAL. All adjustments under this
    Section 10 shall be made by the Board, and its determination as to what
    adjustments shall be made, and the extent thereof, shall be final, binding
    and conclusive.
 
    11. RIGHTS AS A STOCKHOLDER. No shares of Common Stock shall be issued in
respect of the exercise of an Option until full payment therefor has been made,
and the applicable income tax withholding obligation has been satisfied. The
holder of an Option shall have no rights as a stockholder with respect to any
shares covered by the Option until the date a stock certificate (or an
equivalent) for such shares is issued to the holder. Except as otherwise
provided herein, no adjustments shall be made for dividend distributions or
other rights for which the record date is prior to the date such stock
certificate (or an equivalent) is issued.

<PAGE>
    12. TAX WITHHOLDING. As a condition to the exercise of any Option or the
lapse of restrictions on any shares of Common Stock, or in connection with any
other event under the Plan that gives rise to a federal or other governmental
tax withholding obligation on the part of the Company or its Affiliates:
(a) the Company may deduct or withhold (or cause to be deducted or withheld)
from any payment or distribution to an optionee whether or not pursuant to the
Plan, and (b) the Company shall be entitled to require that the optionee remit
cash to the Company (through payroll deduction or otherwise), in each case in an
amount sufficient in the opinion of the Company to satisfy such withholding
obligation. If the event giving rise to the withholding obligation involves a
transfer of shares of Common Stock, then, unless the applicable agreement
provides otherwise, at the discretion of the Committee, the optionee may satisfy
the withholding obligation described under this Section 12 by electing to have
the Company withhold shares of Common Stock (which withholding shall be at a
rate not in excess of the statutory minimum rate) or by tendering
previously-owned shares of Common Stock, in each case having a Fair Market Value
equal to the amount of tax to be withheld (or by any other mechanism as may be
required or appropriate to conform with local tax and other rules).
 
    13. AMENDMENT AND TERMINATION. The Board may amend or terminate the Plan at
any time, provided that no such action may adversely affect the rights of the
holder of any outstanding Option without his or her consent. Except as otherwise
provided in Section 10, any amendment which increases the aggregate number of
shares of Common Stock that may be issued under the Plan, modifies the class of
employees eligible to receive Options under the Plan or otherwise requires
stockholder approval shall, to the extent required by applicable law, be subject
to the approval of the Company's stockholders. The Committee may amend the terms
of any agreement or certificate made or issued hereunder at any time and from
time to time provided that any amendment which would adversely affect the rights
of the holder may not be made without his or her consent.
 
    14. TERM OF THE PLAN. The Plan shall be effective on the Effective Date. The
Plan will terminate on the tenth anniversary of the Effective Date, unless
sooner terminated by the Board. The rights of any person with respect to an
Option granted under the Plan that is outstanding at the time of the termination
of the Plan shall not be affected solely by reason of the termination of the
Plan and shall continue in accordance with the terms of the Option (as then in
effect or thereafter amended) and the Plan.
 
    15. MISCELLANEOUS.
 
        (a) Documentation. Each Option granted made under the Plan shall be
    evidenced by a written agreement or other written instrument the terms of
    which shall be established by the Committee. To the extent not inconsistent
    with the provisions of the Plan, the written agreement or other instrument
    evidencing an Option shall govern the rights and obligations of the optionee
    (and any person claiming through the optionee) with respect to the Option.
 
        (b) NO RIGHTS CONFERRED. Nothing contained herein shall be construed to
    confer upon any individual any right to be retained in the employ or other
    service of the Company or its Affiliates or to interfere with the right of
    the Company or its Affiliates to terminate an optionee's employment or other
    service at any time.
 
        (c) GOVERNING LAW. The Plan shall be governed by the laws of the State
    of Delaware, without regard to its principles of conflicts of law.
 
        (d) DECISIONS AND DETERMINATIONS. All decisions or determinations made
    by the Board and, except to the extent rights or powers under the Plan are
    reserved specifically to the discretion of the Board, all decisions and
    determinations of the Committee, shall be final, binding and conclusive.
 
        (e) SEVERABILITY. In the event any provision of the Plan shall be held
    illegal or invalid for any reason, the illegality or invalidity shall not
    affect the remaining parts of the Plan, and the Plan shall be construed and
    enforced as if the illegal or invalid provision had not been included.

<PAGE>
        (f) REQUIREMENTS OF LAW. The grant of Options and issuance of shares
    under the Plan shall be subject to compliance with all applicable laws,
    rules, and regulations, and to such approvals by any governmental agencies
    or national securities exchanges as the Committee deems necessary or
    desirable.
 
        (g) LISTING AND OTHER CONDITIONS. As long as the Common Stock is listed
    on a national securities exchange or system sponsored by a national
    securities association, the issue of any shares of Common Stock pursuant to
    an Option shall be conditioned upon such shares being listed on such
    exchange or system. If at any time counsel to the Company shall be of the
    opinion that any sale or delivery of shares of Common Stock pursuant to an
    Option is or may in the circumstances be unlawful or result in the
    imposition of excise taxes on the Company under the statutes, rules or
    regulations of any applicable jurisdiction, the Company shall have no
    obligation to make such sale or delivery, or to make any application or to
    effect or to maintain any qualification or registration under the Securities
    Act or otherwise with respect to shares of Common Stock or Options, and the
    right to exercise any Option shall be suspended until, in the opinion of
    said counsel, such sale or delivery shall be lawful or shall not result in
    the imposition of excise taxes on the Company.

<PAGE>
                         ALEXION PHARMACEUTICALS, INC.
 
               THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS
                     FOR THE ANNUAL MEETING OF STOCKHOLDERS
                        TO BE HELD ON DECEMBER 8, 2000.
 
    Leonard Bell, M.D. and David W. Keiser, and each of them, as the true and
lawful attorneys, agents and proxies of the undersigned, with full power of
substitution, are hereby authorized to represent and to vote all shares of
Common Stock of Alexion Pharmaceuticals, Inc. held of record by the undersigned
on October 26, 2000, at the Annual Meeting of Stockholders to be held at
10:00 a.m. on Friday, December 8, 2000, at the Park Avenue Room at the Hotel
Inter-Continental, 111 East 48th Street, New York, New York 10017 and any
adjournment thereof. Any and all proxies heretofore given are hereby revoked.
 
    WHEN PROPERLY EXECUTED, THIS PROXY WILL BE VOTED AS DESIGNATED BY THE
UNDERSIGNED. IF NO CHOICE IS SPECIFIED, THE PROXY WILL BE VOTED FOR EACH OF THE
NOMINEES FOR DIRECTOR LISTED BELOW.
 

<TABLE>
<S>  <C>                                    <C>                                    <C>
1.   Proposal--Election of Directors--Nominees are:
     John H. Fried, Leonard Bell, Jerry T. Jackson, Max Link, Joseph A. Madri, R. Douglas Norby and Alvin S. Parven.
 
     / /  FOR all listed nominees (except do not vote for the nominee(s) whose name(s) appears(s) below):
 
     -------------------------------------------------------------------------------------------------------------------
     / /  WITHHOLD AUTHORITY to vote for the listed nominees.
 
2.   Proposal No. 2--Approval of the Amendment to the Company's 1992 Stock Option Plan to increase the formula option
     grants provided for thereunder.
     / /  FOR                               / /  AGAINST                           / /  ABSTAIN
</TABLE>

 

<PAGE>

<TABLE>
<S>  <C>                                    <C>                                    <C>
3.   Proposal No. 3--Adoption of the Company's 2000 Stock Option Plan.
     / /  FOR                               / /  AGAINST                           / /  ABSTAIN
 
4.   Proposal No. 4--Amendment of the Company's Certificate of Incorporation to increase the Company's authorized
     shares.
     / /  FOR                               / /  AGAINST                           / /  ABSTAIN
 
5.   Proposal No. 5--Appointment of Arthur Andersen LLP as the Company's independent public accountants.
     / /  FOR                               / /  AGAINST                           / /  ABSTAIN
</TABLE>

 
    Discretionary authority is hereby granted with respect to such other matters
as may properly come before the meeting.
 
IMPORTANT: PLEASE SIGN EXACTLY AS NAME APPEARS BELOW. EACH JOINT OWNER SHALL
SIGN. EXECUTORS, ADMINISTRATORS, TRUSTEES, ETC. SHOULD GIVE FULL TITLE AS SUCH.
IF SIGNOR IS A CORPORATION, PLEASE GIVE FULL CORPORATE NAME BY DULY AUTHORIZED
OFFICER. IF A PARTNERSHIP, PLEASE SIGN IN PARTNERSHIP NAME BY AUTHORIZED PERSON.
 
                                              DATED ______________________, 2000
 
                                              __________________________________

                                                          SIGNATURE
 
                                              __________________________________
                                                  SIGNATURE IF HELD JOINTLY
 
                                              THE ABOVE-SIGNED ACKNOWLEDGES
                                              RECEIPT OF THE NOTICE OF ANNUAL
                                              MEETING OF STOCKHOLDERS AND THE
                                              PROXY STATEMENT FURNISHED
                                              THEREWITH.
 
                                              PLEASE SIGN, DATE AND RETURN THIS
                                              PROXY CARD PROMPTLY USING THE
                                              ENCLOSED ENVELOPE.