UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 SCHEDULE 13G (AMENDMENT NO. 1- FINAL AMENDMENT) 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) December 31, 2005 ----------------------------------------- (Date of Event which Requires Filing of this Statement) Check the appropriate box to designate the rule pursuant to which this 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 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 13G PAGE 2 of 9 PAGES 1 NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Ziff Asset Management, L.P. 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 5 SOLE VOTING POWER NUMBER OF 0 SHARES 6 SHARED VOTING POWER BENEFICIALLY 1,208,321 OWNED BY EACH 7 SOLE DISPOSITIVE POWER 0 REPORTING PERSON 8 SHARED DISPOSITIVE POWER WITH 1,208,321 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,208,321 10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) |_| 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 3.9% 12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) PN CUSIP NO. 015351109 13G PAGE 3 of 9 PAGES 1 NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) PBK Holdings, Inc. 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 5 SOLE VOTING POWER NUMBER OF 0 SHARES 6 SHARED VOTING POWER BENEFICIALLY 1,208,321 OWNED BY EACH 7 SOLE DISPOSITIVE POWER 0 REPORTING PERSON 8 SHARED DISPOSITIVE POWER WITH 1,208,321 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,208,321 10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) |_| 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 3.9% 12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) CO CUSIP NO. 015351109 13G PAGE 4 of 9 PAGES 1 NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY) Philip B. Korsant 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 of America 5 SOLE VOTING POWER NUMBER OF 0 SHARES 6 SHARED VOTING POWER BENEFICIALLY 1,208,321 OWNED BY EACH 7 SOLE DISPOSITIVE POWER 0 REPORTING PERSON 8 SHARED DISPOSITIVE POWER WITH 1,208,321 9 AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON 1,208,321 10 CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS) |_| 11 PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9) 3.9% 12 TYPE OF REPORTING PERSON (SEE INSTRUCTIONS) IN ITEM 1. (A) NAME OF ISSUER Alexion Pharmaceuticals, Inc. ITEM 1. (B) ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES 352 Knotter Drive Cheshire, CT 06410 ITEM 2. (A) NAME OF PERSON FILING This Schedule 13G is being filed on behalf of the following persons (the "Reporting Persons")*: (i) Ziff Asset Management, L.P. ("ZAM"); (ii) PBK Holdings, Inc. ("PBK"); and (iii) Philip B. Korsant. * Attached as Exhibit A is a copy of an agreement among the Reporting Persons that this Schedule 13G is being filed on behalf of each of them. ITEM 2. (B) ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE Ziff Asset Management, L.P. 283 Greenwich Avenue Greenwich, CT 06830 PBK Holdings, Inc. 283 Greenwich Avenue Greenwich, CT 06830 Philip B. Korsant 283 Greenwich Avenue Greenwich, CT 06830 ITEM 2. (C) CITIZENSHIP See Item 4 of the attached cover pages. ITEM 2. (D) TITLE OF CLASS OF SECURITIES Common Stock, $0.0001 par value ITEM 2. (E) CUSIP NUMBER 015351109 ITEM 3. Not applicable as this Schedule 13G is filed pursuant to Rule 13d-1(c). ITEM 4. OWNERSHIP (a) Amount beneficially owned: See Item 9 of the attached cover pages. (b) Percent of class: See Item 11 of the attached cover pages. (c) Number of shares as to which such person has: (i) Sole power to vote or to direct the vote: See Item 5 of the attached cover pages. (ii) Shared power to vote or to direct the vote: See Item 6 of the attached cover pages. (iii) Sole power to dispose or to direct the disposition: See Item 7 of the attached cover pages. (iv) Shared power to dispose or to direct the disposition: See Item 8 of the attached cover pages. ITEM 5. OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS Item 5 is hereby amended and restated in its entirety as follows: If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [X]. ITEM 6. OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON Item 6 is hereby amended and restated in its entirety as follows: Not Applicable. ITEM 7. IDENTIFICATION AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY 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 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. SIGNATURE After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct. Dated: February 13, 2006 ZIFF ASSET MANAGEMENT, L.P. By:PBK Holdings, Inc., its general partner By:/s/ DAVID GRAY ----------------------------- Name: David Gray Title: Vice President PBK HOLDINGS, INC. By:/s/ DAVID GRAY ------------------------------ Name: David Gray Title: Vice President /s/ PHILIP B. KORSANT ------------------------------ Philip B. Korsant EXHIBIT A The undersigned, Ziff Asset Management, L.P., a Delaware limited partnership, PBK Holdings, Inc., a Delaware corporation, and Philip B. Korsant hereby agree and acknowledge that the information required by this Schedule 13G, to which this Agreement is attached as an exhibit, is filed on behalf of each of them. The undersigned further agree that any further amendments or supplements thereto shall also be filed on behalf of each of them. Dated: February 13, 2006 ZIFF ASSET MANAGEMENT, L.P. By:PBK Holdings, Inc., its general partner By:/s/ DAVID GRAY ----------------------------- Name: David Gray Title: Vice President PBK HOLDINGS, INC. By:/s/ DAVID GRAY ------------------------------ Name: David Gray Title: Vice President /s/ PHILIP B. KORSANT ------------------------------ Philip B. Korsant