SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934


                          Alexion Pharmaceuticals, Inc.
                                (Name of Issuer)


                         Common Stock, $0.0001 par value
                         (Title of Class of Securities)


                                    015351109
                                 (CUSIP Number)


                                February 24, 2006
             (Date of Event Which Requires Filing of this Statement)

Check the following box to designate the rule pursuant to which the Schedule is
filed:

  [ ]   Rule 13d-1(b)
  [X]   Rule 13d-1(c)
  [ ]   Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).









CUSIP NO. 015351109

   1.    NAMES OF REPORTING PERSONS
         I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
         D. E. Shaw Valence Portfolios, L.L.C.
         13-4046559

   2.    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                   (A)  [ ]
                                                                   (B)  [ ]

   3.    SEC USE ONLY

   4.    CITIZENSHIP OR PLACE OF ORGANIZATION
         Delaware

NUMBER OF                 5.  SOLE VOTING POWER
SHARES                        -0-
BENEFICIALLY
OWNED BY                  6.  SHARED VOTING POWER
EACH                          1,771,517
REPORTING
PERSON WITH               7.  SOLE DISPOSITIVE POWER
                              -0-

                          8.  SHARED DISPOSITIVE POWER
                              1,771,517

   9.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         1,771,517

   10.   CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
         (SEE INSTRUCTIONS)  [ ]

   11.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
         5.7%

   12.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
         OO





CUSIP NO. 015351109

   1.    NAMES OF REPORTING PERSONS
         I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
         D. E. Shaw & Co., L.P.
         13-3695715

   2.    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                     (A)  [ ]
                                                                     (B)  [ ]

   3.    SEC USE ONLY

   4.    CITIZENSHIP OR PLACE OF ORGANIZATION
         Delaware

NUMBER OF                 5. SOLE VOTING POWER
SHARES                       -0-
BENEFICIALLY
OWNED BY                  6. SHARED VOTING POWER
EACH                         1,771,517
REPORTING
PERSON WITH               7. SOLE DISPOSITIVE POWER
                             -0-

                          8. SHARED DISPOSITIVE POWER
                             1,772,712

   9.    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
         1,772,712

   10.   CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
         (SEE INSTRUCTIONS)  [ ]

   11.   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
         5.7%

   12.   TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
         IA, PN




CUSIP NO. 015351109

      1.   NAMES OF REPORTING PERSONS
           I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
           David E. Shaw

      2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
                                                                      (A) [ ]
                                                                      (B) [ ]

      3.   SEC USE ONLY

      4.   CITIZENSHIP OR PLACE OF ORGANIZATION
           United States

NUMBER OF             5. SOLE VOTING POWER
SHARES                   -0-
BENEFICIALLY
OWNED BY              6. SHARED VOTING POWER
EACH                     1,771,517
REPORTING
PERSON WITH           7. SOLE DISPOSITIVE POWER
                         -0-

                      8. SHARED DISPOSITIVE POWER
                         1,772,712

      9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
           1,772,712

      10.  CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
          (SEE INSTRUCTIONS) [ ]

      11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
           5.7%

      12.  TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
           IN








ITEM 1.
     (A) NAME OF ISSUER:
         Alexion Pharmaceuticals, Inc.

     (B) ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES:
         352 Knotter Drive
         Cheshire, CT 06511

ITEM 2.
     (A) NAME OF PERSON FILING:
         D. E. Shaw Valence Portfolios, L.L.C.
         D. E. Shaw & Co., L.P.
         David E. Shaw

     (B) ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE:
         The business address for each reporting person is:
         120 W. 45th Street,
         Tower 45, 39th Floor
         New York, NY 10036

     (C) CITIZENSHIP:
         D. E. Shaw Valence Portfolios, L.L.C. is a limited liability company
         organized under the laws of the state of Delaware.
         D. E. Shaw & Co., L.P. is a limited partnership organized under the
         laws of the state of Delaware.
         David E. Shaw is a citizen of the United States of America.

     (D) TITLE OF CLASS OF SECURITIES:
         Common Stock, $0.0001 par value

     (E) CUSIP NUMBER:
         015351109

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13D-1(B) OR 13D-2(B) OR (C),
CHECK WHETHER THE PERSON FILING IS A:

Not applicable

ITEM 4. OWNERSHIP

As of March 3, 2006:

(a) Amount beneficially owned:

D. E. Shaw Valence Portfolios, L.L.C.          1,771,517 shares
                                               This is composed of (i) 623,317
                                               shares in the name of D. E. Shaw
                                               Valence Portfolios, L.L.C. and
                                               (ii) 1,148,200 shares that
                                               D. E. Shaw Valence, L.L.C. has
                                               the right to acquire through the
                                               exercise of listed call options.

D. E. Shaw & Co., L.P.:                        1,772,712 shares
                                               This is composed of (i) 623,317
                                               shares in the name of D. E. Shaw
                                               Valence Portfolios, L.L.C., (ii)
                                               1,148,200 shares that D. E. Shaw
                                               Valence, L.L.C. has the right to
                                               acquire through the exercise of
                                               listed call options, and (iii)
                                               1,195 shares under the management
                                               of D. E. Shaw Investment
                                               Management, L.L.C.

David E. Shaw:                                 1,772,712 shares
                                               This is composed of (i) 623,317
                                               shares in the name of D. E. Shaw
                                               Valence Portfolios, L.L.C., (ii)
                                               1,148,200 shares that D. E. Shaw
                                               Valence, L.L.C. has the right to
                                               acquire through the exercise of
                                               listed call options, and (iii)
                                               1,195 shares under the management
                                               of D. E. Shaw Investment
                                               Management, L.L.C.



(b) Percent of class:
    D. E. Shaw Valence Portfolios, L.L.C.:             5.7%
    D. E. Shaw & Co., L.P.:                            5.7%
    David E. Shaw:                                     5.7%

(c) Number of shares to which the person has:
    (i)    Sole power to vote or to direct the vote:
           D. E. Shaw Valence Portfolios, L.L.C.:          -0- shares
           D. E. Shaw & Co., L.P.:                         -0- shares
           David E. Shaw:                                  -0- shares

    (ii)   Shared power to vote or to direct the vote:
           D. E. Shaw Valence Portfolios, L.L.C.:          1,771,517 shares
           D. E. Shaw & Co., L.P.:                         1,771,517 shares
           David E. Shaw:                                  1,771,517 shares

    (iii)  Sole power to dispose or to direct the
           disposition of:
           D. E. Shaw Valence Portfolios, L.L.C.:          -0- shares
           D. E. Shaw & Co., L.P.:                         -0- shares
           David E. Shaw:                                  -0- shares

    (iv)   Shared power to dispose or to direct the
           disposition of:
           D. E. Shaw Valence Portfolios, L.L.C.:          1,771,517 shares
           D. E. Shaw & Co., L.P.:                         1,772,712 shares
           David E. Shaw:                                  1,772,712 shares

David E. Shaw does not own any shares directly. By virtue of David E. Shaw's
position as President and sole shareholder of D. E. Shaw & Co., Inc., which is
the general partner of D. E. Shaw & Co., L.P., which in turn is the managing
member and investment adviser of D. E. Shaw Valence Portfolios, L.L.C., and the
managing member of D. E. Shaw Valence, L.L.C. and D. E. Shaw Investment
Management, L.L.C., David E. Shaw may be deemed to have the shared power to vote
or direct the vote of 1,771,517 shares, and the shared power to dispose or
direct the disposition of 1,772,712 shares, the 1,772,712 shares as described
above constituting 5.7% of the outstanding shares and, therefore, David E. Shaw
may be deemed to be the beneficial owner of such shares. David E. Shaw disclaims
beneficial ownership of such 1,772,712 shares.

ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS
Not Applicable

ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON
Not Applicable

ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
        SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY OR CONTROL
        PERSON
Not Applicable

ITEM 8. IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP
Not Applicable

ITEM 9. NOTICE OF DISSOLUTION OF GROUP
Not Applicable

ITEM 10. CERTIFICATION
By signing below, each of D. E. Shaw Valence Portfolios, L.L.C., D. E. Shaw &
Co., L.P., and David E. Shaw certify that, to the best of such reporting
person's knowledge and belief, the securities referred to above were not
acquired and are not held for the purpose of or with the effect of changing or
influencing the control of the issuer of the securities and were not acquired
and are not held in connection with or as a participant in any transaction
having such purposes or effect.








SIGNATURE

After reasonable inquiry and to the best of their knowledge and belief, the
undersigned certify that the information set forth in this statement is true,
complete and correct. A Power of Attorney, dated February 24, 2004, granted by
David E. Shaw in favor of Eric Wepsic, is attached hereto.

Dated: March 6, 2006


                               D. E. Shaw Valence Portfolios, L.L.C.
                               By: D. E. Shaw & Co., L.P., as managing member

                               By: /s/ Eric Wepsic
                                   ---------------------------------------------
                                   Eric Wepsic
                                   Managing Director



                               D. E. Shaw & Co., L.P.

                               By: /s/ Eric Wepsic
                                   ---------------------------------------------
                                   Eric Wepsic
                                   Managing Director




                               David E. Shaw

                               By: /s/ Eric Wepsic
                                   ---------------------------------------------
                                   Eric Wepsic
                                   Attorney-in-Fact for David E. Shaw










                                    EXHIBIT 1

                                POWER OF ATTORNEY
                               FOR CERTAIN FILINGS
                    UNDER THE SECURITIES EXCHANGE ACT OF 1934


I, David E. Shaw, hereby make, constitute and appoint each of:


         Anne Dinning,

         Julius Gaudio,

         Lou Salkind,

         Stuart Steckler, and

         Eric Wepsic,

acting individually, as my agent and attorney-in-fact, with full power of
substitution, for the purpose of, from time to time, executing in my name and/or
my capacity as President of D. E. Shaw & Co., Inc. (acting for itself or as the
general partner of D. E. Shaw & Co., L. P. and general partner or managing
member of other entities, any which in turn may be acting for itself or other
entities) all documents, certificates, instruments, statement, other filings,
and amendments to the forgoing (collectively, "documents") determined by such
person to be necessary or appropriate to comply with ownership or control-person
reporting requirements imposed by any United States or non-United States
governmental or regulatory authority, including without limitation Forms 3, 4,
5, 13D, 13F, and 13G required to be filed with the Securities and Exchange
Commission; and delivering, furnishing or filing any such documents with the
appropriate governmental or regulatory authority. Any such determination shall
be conclusively evidenced by such person's execution, delivery, furnishing,
and/or filing of the applicable document.

This power of attorney shall be valid from the date hereof and replaces the
power granted on February 5, 2001, which is hereby cancelled.

IN WITNESS HEREOF, I have executed this instrument as of the date set forth
below.

Date: February 24, 2004

DAVID E. SHAW, as President of
D. E. Shaw & Co., Inc.
/s/David E. Shaw
New York, New York





                                    EXHIBIT 2

                             JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934,
as amended, each of the undersigned Reporting Persons hereby agrees to the joint
filing, along with all other such Reporting Persons, on behalf of each of them
of a statement on Schedule 13G (including amendments thereto) with respect to
the Common Stock, $0.0001 par value, of Alexion Pharmaceuticals, Inc., and that
this Agreement be included as an Exhibit to such joint filing. This Agreement
may be executed in any number of counterparts, all of which taken together shall
constitute one and the same instrument.

IN WITNESS WHEREOF, each of the undersigned hereby executes this Agreement as of
this 6th day of March, 2006.



                               D. E. Shaw Valence Portfolios, L.L.C.
                               By: D. E. Shaw & Co., L.P., as managing member

                               By: /s/ Eric Wepsic
                                   --------------------------------------------
                                   Eric Wepsic
                                   Managing Director



                               D. E. Shaw & Co., L.P.

                               By: /s/ Eric Wepsic
                                   --------------------------------------------
                                   Eric Wepsic
                                   Managing Director


                                   David E. Shaw

                               By: /s/ Eric Wepsic
                                   --------------------------------------------
                                   Eric Wepsic
                                   Attorney-in-Fact for David E. Shaw