FIRST AMENDMENT TO CREDIT AGREEMENT

Exhibit 10.24(a)

FIRST AMENDMENT TO CREDIT AGREEMENT

THIS FIRST AMENDMENT TO CREDIT AGREEMENT (this “Amendment”) is entered into as of October 20, 2004 by and among RELIANT PHARMACEUTICALS, INC., a Delaware corporation, (the “Borrower”), the financial institutions parties hereto, each as a Lender, MERRILL LYNCH CAPITAL, a division of Merrill Lynch Business Financial Services Inc., as Agent, and each of the other Persons who are signatories hereto (Borrower and each such Person is individually referred to herein as a “Credit Party” and collectively as the “Credit Parties”).

W I T N E S S E T H:

WHEREAS, Borrower, Agent and Lenders have entered into that certain Credit Agreement dated as of August 19, 2004 (as the same may be amended, restated, supplemented or otherwise modified from time to time, the “Credit Agreement”); and

WHEREAS, the parties to the Credit Agreement desire to amend the Credit Agreement on the terms and subject to the conditions set forth herein; and

NOW, THEREFORE, in consideration of the mutual agreements, provisions and covenants contained herein, the parties agree as follows:

1. Defined Terms. Capitalized terms used but not defined herein shall have the meanings ascribed to them in the Credit Agreement.

2. Amendments.

(a) Section 1.1 of the Credit Agreement is hereby amended by deleting the definition of “Account” contained therein in its entirety, and substituting the following language therefor:

“ “Account” means, collectively, (a) any accounts receivable for goods sold and services rendered by Borrower (including, without limitation, all promotional fees, service fees and other similar fees owing to Borrower from Novartis under and as described in the Novartis Agreement) or any of Borrower’s Subsidiaries, and rents, license fees, and “payment intangibles” (as that term is defined in the UCC now or hereafter in effect) in respect of the foregoing and (b) all proceeds of any of the foregoing.”

(b) Section 1.1 of the Credit Agreement is hereby amended by adding the following definition of “Primary Collateral” thereto in the appropriate alphabetical order:

“ “Primary Collateral” shall have the meaning ascribed to such term in that certain Amended and Restated Security Agreement dated as of September 3, 2004 between Borrower and Agent, as the same may be amended, restated, supplemented or otherwise modified and in effect from time to time.”

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(c) Subsections 2.10(d),(e) and (i) of the Credit Agreement are each hereby amended by replacing the term “Collateral” contained therein with the term “Primary Collateral.”

(d) Section 4.9 of the Credit Agreement is hereby deleted in its entirety, with the following language substituted therefor:

“Section 4.9 Further Assurances.

Borrower will, and will cause each Subsidiary to, at its own cost and expense, cause to be promptly and duly taken, executed, acknowledged and delivered all such further acts, documents and assurances as may from time to time be necessary or as Agent or the Required Lenders may from time to time reasonably request in order to carry out the intent and purposes of the Financing Documents and the transactions contemplated thereby, including all such actions to establish, preserve, protect and perfect: (i) a first priority Lien (subject only to Permitted Liens) in favor of Agent for the benefit of Lenders on the Primary Collateral (including Primary Collateral acquired after the date hereof), whether now owned or hereafter acquired, and (ii) a Lien (subject only to Permitted Liens) in favor of Agent for the benefit of Lenders on the Collateral other than the Primary Collateral (including such Collateral other than the Primary Collateral acquired after the date hereof), whether now owned or hereafter acquired. Borrower will cause each hereafter acquired Subsidiary to, within ten (10) Business Days of the acquisition of such Subsidiary and at its own cost and expense, execute a joinder to the Subsidiary Guaranty and the Subsidiary Security Agreement, and such other documents and agreements as Agent may reasonably require to obtain a first or second, as applicable, priority perfected security interests in the assets of such Subsidiary (subject to Permitted Liens, and otherwise consistent with the Security Interests granted to Agent by Borrower in the Security Documents), all in form and substance reasonably acceptable to Agent.”

(e) Section 5.2 of the Credit Agreement is hereby amended by replacing the term “Collateral” contained in the second line thereof with the term “Primary Collateral.”

(f) Subsection 5.2(m) and Sections 5.6 and 5.12 of the Credit Agreement are hereby amended by replacing each usage of the term “Collateral” contained therein with the term “Primary Collateral.”

3. Conditions. The effectiveness of this Amendment is subject to the following conditions precedent:

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4. Representations and Warranties. Each Credit Party hereby represents and warrants to Agent and each Lender as follows:

5. No Waiver. Nothing contained herein shall be deemed to constitute a waiver of compliance with the financial covenants contained in Article 7 of the Credit Agreement, a waiver of compliance with any other term or condition contained in the Credit Agreement or any of the other Financing Documents or constitute a course of conduct or dealing among the parties. Except as expressly stated herein, Agent and Lender reserve all rights, privileges and remedies under the Financing Documents. Except as amended hereby, the Credit Agreement and other Financing Documents remain unmodified and in full force and effect. All references in the Financing Documents to the Credit Agreement shall be deemed to be references to the Credit Agreement as amended hereby.

6. Severability. In case any provision of or obligation under this Amendment shall be invalid, illegal or unenforceable in any jurisdiction, the validity, legality and enforceability of the remaining provisions or obligations, or of such provision or obligation in any other jurisdiction, shall not in any way be affected or impaired thereby.

7. Headings. Headings and captions used in this Amendment (including the Exhibits, Schedules and Annexes hereto, if any) are included for convenience of reference only and shall not be given any substantive effect.

8. GOVERNING LAW; SUBMISSION TO JURISDICTION. THIS AMENDMENT SHALL BE GOVERNED BY, AND SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH THE LAWS OF THE STATE OF ILLINOIS,

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WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES. EACH CREDIT PARTY HEREBY CONSENTS TO THE JURISDICTION OF ANY STATE OR FEDERAL COURT LOCATED WITHIN THE COUNTY OF COOK, STATE OF ILLINOIS AND IRREVOCABLY AGREES THAT, SUBJECT TO AGENT’S ELECTION, ALL ACTIONS OR PROCEEDINGS ARISING OUT OF OR RELATING TO THIS AMENDMENT OR THE OTHER FINANCING DOCUMENTS SHALL BE LITIGATED IN SUCH COURTS. EACH CREDIT PARTY EXPRESSLY SUBMITS AND CONSENTS TO THE JURISDICTION OF THE AFORESAID COURTS AND WAIVES ANY DEFENSE OF FORUM NON CONVENIENS. EACH CREDIT PARTY HEREBY WAIVES PERSONAL SERVICE OF ANY AND ALL PROCESS AND AGREES THAT ALL SUCH SERVICE OF PROCESS MAY BE MADE UPON SUCH PERSON BY CERTIFIED OR REGISTERED MAIL, RETURN RECEIPT REQUESTED, ADDRESSED C/O BORROWER AT THE ADDRESS SET FORTH IN THE CREDIT AGREEMENT AND SERVICE SO MADE SHALL BE COMPLETE TEN (10) DAYS AFTER THE SAME HAS BEEN POSTED.

10. WAIVER OF JURY TRIAL. EACH CREDIT PARTY, AGENT AND THE LENDERS HEREBY IRREVOCABLY WAIVE ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THE FINANCING DOCUMENTS OR THE TRANSACTIONS CONTEMPLATED THEREBY AND AGREES THAT ANY SUCH ACTION OR PROCEEDING SHALL BE TRIED BEFORE A COURT AND NOT BEFORE A JURY.

11. Waiver. Borrower and each other Credit Party, on behalf of each such Credit Party and their respective executors, successors and assigns, hereby waives, releases and discharges Agent and the Lenders and all of the affiliates, directors, officers, employees, attorneys and agents of Agent and the Lenders, from any and all claims, demands, actions or causes of action arising out of or in any way relating to the Financing Documents occurring on or before the date hereof and any documents, agreements, dealings or other matters connected with the Financing Documents, including, without limitation, all known and unknown matters, claims or transactions occurring on or before the date hereof.

12. Counterparts; Integration. This Amendment may be executed and delivered via facsimile with the same force and effect as if an original were executed and may be signed in any number of counterparts, each of which shall be an original, with the same effect as if the signatures hereto were upon the same instrument. This Amendment constitutes the entire agreement and understanding among the parties hereto with respect to the subject matter hereof and supersede any and all prior agreements and understandings, oral or written, relating to the subject matter hereof.

13. Reaffirmation. Each of the Credit Parties as debtor, grantor, guarantor, assignor, as applicable, or in any other similar capacity in which such Credit Party grants liens or security interests in its property or otherwise acts as accommodation party or guarantor, as the case may be, hereby (i) ratifies and reaffirms all of its payment and performance obligations, contingent or otherwise, under each of the Financing Documents to which it is a party (after giving effect hereto) and (ii) to the extent such Credit Party granted liens on or security interests in any of its property pursuant to any such Financing Document as security for or otherwise guaranteed the Borrower’s Obligations under or with respect to the Financing Documents, ratifies and reaffirms

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such guarantee and grant of security interests and liens and confirms and agrees that such security interests and liens hereafter secure all of the Obligations as amended hereby. Each of the Credit Parties hereby consents to this Amendment and acknowledges that each of the Financing Documents remains in full force and effect and is hereby ratified and reaffirmed. The execution of this Amendment shall not operate as a waiver of any right, power or remedy of the Agent or Lenders, constitute a waiver of any provision of any of the Financing Documents or serve to effect a novation of the Obligations.

[ Remainder of Page Intentionally Left Blank; Signature Page Follows ]

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IN WITNESS WHEREOF, the parties have executed this Amendment as of the date set forth above.

First Amendment to Credit Agreement