UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
 
 
SCHEDULE 13G
(Rule 13d-102)
 
Information Statement Pursuant to Rules 13d-1 and 13d-2
Under the Securities Exchange Act of 1934
(Amendment No. 3)*
 
Alexion Pharmaceuticals, Inc.
(Name of Issuer)
 
Common Stock
(Title of Class of Securities)
 
015351109
(CUSIP Number)
 
December 31, 2006
Date of Event Which Requires Filing of the Statement

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
 
o Rule 13d-1(b)
x Rule 13d-1(c)
o 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 disclosures provided in a prior cover page.
 
The information required on 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).

Page 1 of 11
CUSIP NO. 015351109
13G
Page 2 of 11 Pages
 
 
1.
 
NAME OF REPORTING PERSON
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Citadel Limited Partnership
 
2.
 
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) x 
 
3.
 
SEC USE ONLY
 
4.
 
CITIZENSHIP OR PLACE OF ORGANIZATION
Illinois limited partnership
 
 
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
 
5.
 
SOLE VOTING POWER
0
 
6.
 
SHARED VOTING POWER
 
1,874,402 shares
 
7.
 
SOLE DISPOSITIVE POWER
0
 
8.
 
SHARED DISPOSITIVE POWER
See Row 6 above.
 
9.
 
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
See Row 6 above.
 
10.
 
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES                                    o          
 
11.
 
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
Approximately 5.2% as of the date of this filing
 
12.
 
TYPE OF REPORTING PERSON
PN; HC

Page 2 of 11
CUSIP NO. 015351109
13G
Page 3 of 11 Pages
 
 
1.
 
NAME OF REPORTING PERSON
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Citadel Investment Group, L.L.C.
 
2.
 
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) x 
 
3.
 
SEC USE ONLY
 
4.
 
CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware limited liability company
 
 
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
 
5.
 
SOLE VOTING POWER
0
 
6.
 
SHARED VOTING POWER
 
1,874,402 shares
 
7.
 
SOLE DISPOSITIVE POWER
0
 
8.
 
SHARED DISPOSITIVE POWER
See Row 6 above.
 
9.
 
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
See Row 6 above.
 
10.
 
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES                                o          
 
11.
 
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
Approximately 5.2% as of the date of this filing
 
12.
 
TYPE OF REPORTING PERSON
OO; HC

Page 3 of 11
CUSIP NO. 015351109
13G
Page 4 of 11 Pages
 
 
1.
 
NAME OF REPORTING PERSON
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Kenneth Griffin
 
2.
 
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) x 
(b) o 
 
3.
 
SEC USE ONLY
 
4.
 
CITIZENSHIP OR PLACE OF ORGANIZATION
U.S. Citizen
 
 
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
 
5.
 
SOLE VOTING POWER
0
 
6.
 
SHARED VOTING POWER
 
1,874,402 shares
 
7.
 
SOLE DISPOSITIVE POWER
0
 
8.
 
SHARED DISPOSITIVE POWER
See Row 6 above.
 
9.
 
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
See Row 6 above.
 
10.
 
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES                                    o          
 
11.
 
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
Approximately 5.2% as of the date of this filing
 
12.
 
TYPE OF REPORTING PERSON
IN; HC

Page 4 of 11
CUSIP NO. 015351109
13G
Page5 of 11 Pages
 
 
1.
 
NAME OF REPORTING PERSON
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Citadel Equity Fund Ltd.
 
2.
 
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) x 
(b) o 
 
3.
 
SEC USE ONLY
 
4.
 
CITIZENSHIP OR PLACE OF ORGANIZATION
Cayman Islands company
 
 
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
 
5.
 
SOLE VOTING POWER
0
 
6.
 
SHARED VOTING POWER
 
1,874,402 shares
 
7.
 
SOLE DISPOSITIVE POWER
0
 
8.
 
SHARED DISPOSITIVE POWER
See Row 6 above.
 
9.
 
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
See Row 6 above.
 
10.
 
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES                                o          
 
11.
 
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
Approximately 5.2% as of the date of this filing
 
 
12.
 
 
TYPE OF REPORTING PERSON
CO

Page 5 of 11
CUSIP NO. 015351109
13G
Page 6 of 11 Pages
 
 
1.
 
NAME OF REPORTING PERSON
S.S. OR I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
 
Citadel Derivatives Group LLC
 
2.
 
CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP
(a) x 
(b) o 
 
3.
 
SEC USE ONLY
 
4.
 
CITIZENSHIP OR PLACE OF ORGANIZATION
Delaware limited liability company
 
 
NUMBER OF
SHARES
BENEFICIALLY
OWNED BY
EACH
REPORTING
PERSON
WITH
 
5.
 
SOLE VOTING POWER
0
 
6.
 
SHARED VOTING POWER
 
1,874,402 shares
 
7.
 
SOLE DISPOSITIVE POWER
0
 
8.
 
SHARED DISPOSITIVE POWER
See Row 6 above.
 
9.
 
AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
See Row 6 above.
 
10.
 
CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES                                o          
 
11.
 
PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
Approximately 5.2% as of the date of this filing
 
 
12.
 
 
TYPE OF REPORTING PERSON
OO; BD

Page 6 of 11
CUSIP NO. 015351109
13G
Page 7 of 11 Pages


Item 1(a) Name of Issuer: ALEXION PHARMACEUTICALS, INC.
         1(b) Address of Issuer’s Principal Executive Offices:
 
352 Knotter Drive
Cheshire, Connecticut 06410

Item 2(a) Name of Person Filing1 
Item 2(b) Address of Principal Business Office
Item 2(c) Citizenship
 
 
Citadel Limited Partnership
 
131 S. Dearborn Street
 
32nd Floor
 
Chicago, Illinois 60603
 
Illinois limited partnership
   
 
Citadel Investment Group, L.L.C.
 
131 S. Dearborn Street
 
32nd Floor
 
Chicago, Illinois 60603
 
Delaware limited liability company
   
 
Kenneth Griffin
 
131 S. Dearborn Street
 
32nd Floor
 
Chicago, Illinois 60603
 
U.S. Citizen

 
Citadel Equity Fund Ltd.
 
c/o Citadel Investment Group, L.L.C.
 
131 S. Dearborn Street
 
32nd Floor
 
Chicago, Illinois 60603
 
Cayman Islands company
   
 
Citadel Derivatives Group LLC
 
c/o Citadel Investment Group, L.L.C.
 
131 S. Dearborn Street
 
32nd Floor
 
Chicago, Illinois 60603
 
Delaware limited liability company
   
1 Citadel Wellington LLC, a Delaware limited liability company ("CW"), and Citadel Kensington Global Strategies Fund Ltd., a Bermuda company ("CKGSF"), collectively own 100% of Citadel Holdings Ltd., a Cayman Islands company ("CH"), which owns 100% of Citadel Equity Fund Ltd. ("CEF"). None of CW, CKGSF or CH has any control over the voting or disposition of securities held by Citadel Equity Fund Ltd. CW and Citadel Limited Partnership collectively own 100% of Citadel Derivatives Group LLC, but CW does not have any control over the voting or disposition of securities held by Citadel Derivatives Group LLC.
 
Page 7 of 11
CUSIP NO. 015351109
13G
Page 8 of 11 Pages
 
2(d) Title of Class of Securities:
 
Common Stock, par value $0.0001.
 
2(e) CUSIP Number:   015351109
 
Item 3  If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:
 
 
(a)
[__]
Broker or dealer registered under Section 15 of the Exchange Act;
 
 
(b)
[__]
Bank as defined in Section 3(a)(6) of the Exchange Act;
 
 
(c)
[__]
Insurance company as defined in Section 3(a)(19) of the Exchange Act;
 
 
(d)
[__]
Investment company registered under Section 8 of the Investment Company Act;
 
 
(e)
[__]
An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);
 
 
(f)
[__]
An employee benefit plan or endowment fund in accordance with Rule 13d-1(b)(1)(ii)(F);
 
 
(g)
[__]
A parent holding company or control person in accordance with Rule 13d-1(b)(1)(ii)(G);
 
 
(h)
[__]
A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act;
 
 
(i)
[__]
A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act;
 
 
(j)
[__]
Group, in accordance with Rule 13d-1(b)(1)(ii)(J).
 
If this statement is filed pursuant to Rule 13d-1(c), check this box. x
 
Item 4  Ownership:
 
CITADEL LIMITED PARTNERSHIP
CITADEL INVESTMENT GROUP, L.L.C.
KENNETH GRIFFIN
CITADEL EQUITY FUND LTD.
CITADEL DERIVATIVES GROUP LLC

(a) Amount beneficially owned:
 
1,874,402 shares
 
Page 8 of 11
CUSIP NO. 015351109
13G
Page 9 of 11 Pages
 
(b) Percent of Class: 
 
Approximately 5.2% as of the date of this filing
 
(c) Number of shares as to which such person has:
 
(i) sole power to vote or to direct the vote:
 
     
0
 
(ii) shared power to vote or to direct the vote:
 
See Item 4(a) above.
 
(iii) sole power to dispose or to direct the disposition of:
 
     
0
 
(iv) shared power to dispose or to direct the disposition of:
 
See Item 4(a) above.
 
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:

See Item 2 above.

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 I certify that, to the best of my 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 that purpose or effect.
 
Page 9 of 11
CUSIP NO. 015351109
13G
Page 10 of 11 Pages
 
* John C. Nagel is signing on behalf of Kenneth Griffin as attorney-in-fact pursuant to a power of attorney previously filed with the Securities and Exchange Commission on February 24, 2006, and hereby incorporated by reference herein. The power of attorney was filed as an attachment to a filing by Citadel Limited Partnership on Schedule 13G for Morgans Hotel Group Co.
 

Page 10 of 11
CUSIP NO. 015351109
13G
Page 11 of 11 Pages

After reasonable inquiry and to the best of its knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct.
 
Dated this 13th day of February, 2007

KENNETH GRIFFIN
 
By: /s/ John C. Nagel           
John C. Nagel, attorney-in-fact*
 
CITADEL LIMITED PARTNERSHIP
 
By: Citadel Investment Group, L.L.C.,
its General Partner
 
By: /s/ John C. Nagel           
John C. Nagel, Director and
Associate General Counsel
 
CITADEL DERIVATIVES GROUP LLC
 
By: Citadel Limited Partnership,
its Managing Member
 
By: Citadel Investment Group, L.L.C.,
its General Partner
 
By: /s/ John C. Nagel           
John C. Nagel, Director and
Associate General Counsel
CITADEL EQUITY FUND LTD.
 
By: Citadel Limited Partnership,
its Portfolio Manager
 
By: Citadel Investment Group, L.L.C.,
its General Partner
 
By: /s/ John C. Nagel           
John C. Nagel, Director and
Associate General Counsel
 
CITADEL INVESTMENT GROUP, L.L.C.
 
By: /s/ John C. Nagel           
John C. Nagel, Director and
Associate General Counsel
 
 
 
Page 11 of 11