FIRST AMENDMENT TO RECEIVABLES PURCHASE AGREEMENT

Exhibit 4.29

FIRST AMENDMENT TO RECEIVABLES PURCHASE AGREEMENT

THIS FIRST AMENDMENT TO RECEIVABLES PURCHASE AGREEMENT, dated as of December 12, 2003 (this “Amendment”) is entered into among AMERISOURCE RECEIVABLES FINANCIAL CORPORATION, a Delaware corporation (in such capacity, the “Seller”), AMERISOURCEBERGEN DRUG CORPORATION, a Delaware corporation, as the initial Servicer (in such capacity, the “Servicer”), the VARIOUS PURCHASER GROUPS FROM TIME TO TIME PARTY THERETO, and WACHOVIA BANK, NATIONAL ASSOCIATION, a national banking association, as administrator for each of the Purchaser Groups party thereto (together with its successors and assigns in such capacity, the “Administrator”).

RECITALS

A. The Seller, Servicer, the various other Purchaser Groups from time to time party thereto and the Administrator have entered into that certain Receivables Purchase Agreement, dated as of July 10, 2003 (as amended, supplemented or otherwise modified from time to time, the “Agreement”).

B. The parties to the Agreement desire to enter into this Amendment to amend the Agreement.

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties agree as follows:

1. Certain Defined Terms. Capitalized terms used but not defined herein shall have the meanings set forth for such terms in Exhibit I to the Agreement.

2. Amendments to the Agreement. The Agreement is hereby amended as follows:

2.1 The last sentence in the definition of “Obligor Concentration Limit” as set forth in Exhibit I to the Agreement is hereby amended as follows:

As of December 12, 2003, Longs Drug Stores Corporation, AdvancePCS, Inc. and Medco Health Solutions, Inc. shall have a Special Concentration Limit of 8.0%, 5.5% and 4.75%, respectively.

2.2 The definition of “Required Reserve Factor Floor” as set forth in Exhibit I to the Agreement is hereby amended by replacing the reference to “18.5%” therein with “20.75%”.

3. Effect of Amendment. This Amendment shall become effective upon the execution of such Amendment by all of the parties hereto. Except as expressly amended and modified by this Amendment, all provisions of the Agreement shall remain in full force and effect. After this Amendment becomes effective, all references in each of the Agreements to “this Agreement”, “hereof”, “herein”, or words of similar effect referring to such Agreement shall be deemed to be references to the Agreement, as amended by this Amendment. This

Amendment shall not be deemed to expressly or impliedly waive, amend or supplement any provision of the Agreement (or any related document or agreement) other than as set forth herein.

4. Counterparts. This Amendment may be executed in any number of counterparts and by different parties on separate counterparts, and each counterpart shall be deemed to be an original, and all such counterparts shall together constitute but one and the same instrument.

5. Governing Law. This Amendment shall be governed by, and construed in accordance with the law of the State of New York without regard to any otherwise applicable principles of conflicts of law.

6. Section Headings. The various headings of this Amendment are inserted for convenience only and shall not affect the meaning or interpretation of this Amendment, or the Agreements or any provision hereof or thereof.

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IN WITNESS WHEREOF, the parties have caused this Amendment to be executed by their respective officers thereunto duly authorized, as of the date first above written.