Exhibit 10.12.3

Execution Copy

THIRD AMENDMENT AGREEMENT

THIS THIRD AMENDMENT AGREEMENT dated as of January 28, 2003 (this "Amendment Agreement"), by and between VERSICOR INC., a Delaware corporation (the "Company"), andFLEET NATIONAL
BANK(the "Bank").

WHEREAS,
the Bank and the Company wish to modify the provisions of the Loan Agreement (as defined herein) to add a new equipment loan, modify the terms of the Term Loan, and modify
certain financial covenants and other provisions of the Loan Agreement as set forth herein.

NOW,
THEREFORE, in consideration of the foregoing and the agreements contained herein, the parties hereby agree as follows:

1.Reference to Loan Agreement.

Reference
is made to that certain Revolving Credit, Term Loan and Security Agreement dated as of December 31, 1996, as amended by the First Amendment Agreement dated as of
December 30, 1997 and the Second Amendment Agreement dated as of October 22, 2001, and as extended by that certain Extension Letter dated as of December 27, 2002 (as the same may
be further amended, restated, supplemented or otherwise modified from time to time, the "Loan Agreement"), by and between the Company and the Bank.
Capitalized terms used herein which are defined in the Loan Agreement have the same meanings herein as therein, except to the extent that such meanings are amended hereby.

2.Amendments.

The
Company and the Bank agree that the Loan Agreement is hereby amended, effective as of the date hereof, as follows:

(a)Additions to Section 1.1 of the Loan Agreement.The following definitions are hereby added to
Section 1.1 of the Loan Agreement:



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(b)Modifications to Section 1.1 of the Loan Agreement.



(c)Modifications to Section 2 of the Loan Agreement.



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2.8Interest.The Notes shall bear interest on the unpaid principal amount thereof until paid in full at the
rate or rates per annum determined (on the basis of the actual number of days elapsed over a 360-day year) and payable as follows:



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2.9Certain LIBOR Provisions.



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(d)Additions to Section 2 of the Loan Agreement.Sections 2.9A, 2.9B, 2.9C, and 2.9D of the Loan
Agreement as set forth below are hereby added to the Loan Agreement immediately following Section 2.9:



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SECTION 2B
DESCRIPTION OF EQUIPMENT LOANS II



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(g)Amendment to Section 4.Section 4.13 is hereby amended by deleting subsection (b) and
replacing it with the following subsections (b) and (c):



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(h)Amendments to Section 5.



(i)Amendments to Section 6.



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3.No Default; Representations and Warranties, etc.

The
Company hereby confirms that: (a) except as set forth on the Disclosure Schedule attached hereto, the representations and warranties of the Company contained in
Section 4 of the Loan Agreement are true on and as of the date hereof as if made on such date (except to the extent that such representations and warranties expressly relate to an earlier
date); (b) the Company is in compliance in all material respects with all of the terms and provisions set forth in the Loan Agreement on its part to be observed or performed thereunder; and
(c) after giving effect to this Amendment Agreement, no Event of Default specified in Section 8 of the Loan Agreement, nor any event which with the giving of notice or expiration of any
applicable grace period or both would constitute such an Event of Default, shall have occurred and be continuing.

4.Conditions to the Effectiveness of this Amendment Agreement.

Concurrently
herewith (and as conditions to the Bank's consent to this Amendment Agreement), the Company will furnish the Bank with the following:

(a)  This
Amendment Agreement duly executed by the Company;

(b)  The
Term Note duly executed by the Company;

(c)  The
Equipment Note II duly executed by the Company;

(d)  A
Perfection Certificate in the form ofExhibit Hduly completed and executed by the Company;

(e)  A
Pledged Account Agreement in the form ofExhibit Iattached hereto executed by the Company to perfect the Bank's
security interest in the collateral described therein;

(f)    A
certificate of the Secretary or an Assistant Secretary of the Company certifying: (i) the resolutions of the Company's board of directors authorizing the
execution and delivery of this Amendment Agreement, the Equipment Note II, (ii) the identity of the officer(s) authorized to execute, deliver and take all other actions required under
this Amendment Agreement, and the specimen signatures of such officers, (iii) the true, correct and complete copy of the certificate of incorporation of the Company
(together with all amendments thereto), and (iv) the true, correct and complete copy of the Bylaws of the Company (together with all amendments thereto);

(g)  A
certificate of the Secretary of State of the State of Delaware, as to legal existence and good corporate standing of the Company in such state and listing all
documents on file in the office of said Secretary of State;

(h)  A
certificate of the Secretary of State of the State of California, as to the qualification of the Company to transact business in such state;

(i)    A
certificate of the Secretary of the Commonwealth of Pennsylvania, as to the qualification of the Company to transact business in such commonwealth;

(j)    Lien
searches against the Company in all appropriate jurisdictions;

(k)  A
landlord's consent and estoppel with respect to the Company's leasehold properties located in Fremont, California and King of Prussia, Pennsylvania, each in a form
satisfactory to the Bank and its counsel;

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(l)    The
Bank's security interest in the Collateral (as defined in Section 7.1 as amended by this Amendment Agreement) shall continue to be a first priority perfected
security interest subject only to Permitted Encumbrances and such UCC-1 financing statements or UCC-3 continuation statements as may be necessary to maintain such first
priority perfected security interest shall have been filed in all appropriate filing offices;

(m)  Opinion
of O'Melveney & Myers LLP, reasonably acceptable in form and substance to the Bank and its counsel;

(n)  Payment
of the $50,000 facility fee by the Company to the Bank;

(o)  Payment
of all invoiced fees and expenses (including legal fees and disbursements) incurred by the Bank in connection with this Amendment Agreement and the transactions
contemplated hereby; and

(p)  Such
other documents and instruments as the Bank may reasonably require in order to put this Amendment Agreement into full force and effect.

5.Miscellaneous.

(a)  Except
to the extent specifically amended hereby, the Loan Agreement, Loan Documents and all related documents shall remain in full force and effect. Whenever the terms
or sections amended hereby shall be referred to in the Loan Agreement, the Loan Documents or such other documents (whether directly or by incorporation into other defined terms), such defined terms
shall be deemed to refer to those terms or sections as amended by this Amendment Agreement. All references in the Loan Agreement, Loan Documents or such other documents to the Notes shall be deemed to
refer to the Term Note, the Equipment Note and the Equipment Note II.

(b)  This
Amendment Agreement may be executed in any number of counterparts, each of which, when executed and delivered, shall be an original, but all counterparts shall
together constitute one instrument.

(c)  The
Company shall pay all reasonable expenses, including reasonable legal fees and disbursements incurred by the Bank in connection with this Amendment Agreement and the
transactions contemplated hereby and any other expenses, reasonable legal fees and disbursements incurred by the Bank.

(d)  This
Amendment Agreement shall be governed by the laws of the Commonwealth of Massachusetts and shall be binding upon and inure to the benefit of the parties hereto and
their respective successors and assigns.

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remainder of this page is intentionally left blank.]

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IN
WITNESS WHEREOF, the parties hereto have executed this Amendment Agreement which shall be deemed to be a sealed instrument as of the date first above written.

| |  | VERSICOR INC.      
| |  | -------------------
| |  | By:                
| |  | FLEET NATIONAL BANK
| |  | By:                

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