WAIVER AND FIRST AMENDMENT TO CREDIT AGREEMENT

Exhibit 10.2

[EXECUTION COPY]

WAIVER AND FIRST AMENDMENT TO CREDIT AGREEMENT

This WAIVER AND FIRST AMENDMENT TO CREDIT AGREEMENT, dated as of May 7, 2009 (this “ Amendment ”), modifies that certain Credit Agreement, dated as of February 13, 2008 (as amended, restated, extended, supplemented or otherwise modified in writing from time to time, the “ Credit Agreement ”), among ALEXION PHARMACEUTICALS, INC., a Delaware corporation (the “ Borrower ”), each Lender from time to time party thereto (the “ Lenders ”), BANK OF AMERICA, N.A., as administrative agent (in such capacity, the “ Administrative Agent ”) for itself and the other Lenders, and the L/C Issuer. Any capitalized term used herein and not defined shall have the meaning assigned to it in the Credit Agreement.

RECITALS

WHEREAS, the Borrower has informed the Administrative Agent and the Lenders that certain Events of Default have occurred and are continuing solely as a result of the Borrower’s failure to comply with the financial covenants set forth in Sections 7.12(a) and 7.12(b) of the Credit Agreement as of the fiscal year of the Borrower ended December 31, 2008 (the “ Specified Defaults ”);

WHEREAS , the Borrower has requested that the Administrative Agent and the Lenders waive the Specified Defaults and agree to amend certain of the terms and provisions of the Credit Agreement, as specifically set forth in this Amendment; and

WHEREAS , the undersigned Lenders and the Administrative Agent are prepared to waive the Specified Defaults and to amend the Credit Agreement on the terms, subject to the conditions and in reliance on the representations set forth herein.

NOW THEREFORE , in consideration of the premises and other good and valuable consideration, the parties hereto hereby agree as follows:

Section 1. Waiver . Subject to the satisfaction of all of the terms and conditions set forth herein, the undersigned Lenders and the Administrative Agent hereby waive the Specified Defaults solely for the fiscal year ended December 31, 2008. This waiver shall not impair any right or power accruing to any Lender or the Administrative Agent with respect to any other Default or Event of Default or any Default or Event of Default which occurs after the date hereof. Nothing contained herein shall be deemed to imply any willingness of any Lender or the Administrative Agent to agree to, or otherwise prejudice any rights of any Lender or the Administrative Agent with respect to, any similar waiver that may be requested by the Borrower. Upon the occurrence of any Default or Event of Default (other than the Specified Defaults), the Lenders and the Administrative Agent may take any and all actions permitted to be taken by the Lenders and the Administrative Agent under the Credit Agreement, the other Loan Documents and applicable Law.

Section 2. Amendments to Credit Agreement .

(a) Paragraph (a) of Section 7.12 (Capital Expenditures) of the Credit Agreement is hereby amended by restating the table set forth in such Paragraph (a) in its entirety as follows:

(b) Paragraph (b) of Section 7.12 (Capital Expenditures) of the Credit Agreement is hereby amended by restating the table set forth in such Paragraph (b) in its entirety as follows:

Section 3. Condition Precedent . This Amendment shall become effective as of the date first written above (the “ Effective Date ”) upon the satisfaction of the following conditions precedent:

(a) Documentation . Administrative Agent shall have received all of the following, in form and substance satisfactory to Administrative Agent:

(i) a fully-executed and effective Amendment by the Borrower, the Guarantors, the Administrative Agent and the Required Lenders;

(ii) such additional documents, instruments and information as Administrative Agent may reasonably request to effect the transactions contemplated hereby.

(b) No Default . On the Effective Date and after giving effect to this Amendment, no event shall have occurred and be continuing that would constitute an Event of Default or a Default.

(c) Fees . The Administrative Agent, for the person entitled thereto, shall have received payment by the Borrower of any fees and expenses that are due and payable on or prior to the Effective Date.

Section 4. Representations and Warranties; Reaffirmation of Grant . Each Loan Party hereby represents and warrants to the Administrative Agent and the Lenders that, as of the date hereof and after giving effect to this Amendment, (a) all representations and warranties of the Loan Parties set forth in the Credit Agreement and in any other Loan Document are true and correct in all material respects (except that such materiality qualifier shall not be applicable to any representations and warranties that already are qualified or modified by materiality in the text thereof) on and as of the date hereof to the same extent as though made on