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                                                                    EXHIBIT 10.1

                AMENDMENT TO COLLABORATION AND LICENSE AGREEMENT


        This is an Amendment dated as of December 19, 2003 (the "Amendment") to
the Collaboration and License Agreement between Esperion Therapeutics, Inc. (the
"Company") and Pharmacia AB ("PNU"), dated June 24, 1998 (the "Original
Agreement").

                                   Background

        WHEREAS, under the terms of the Original Agreement, the Company acquired
Assigned PNU Patent Rights and licensed PNU Know-How and Licensed PNU Patent
Rights in order to, among other things, develop the Compound as a therapeutic
for the cardiovascular market;

        WHEREAS, Pfizer Inc. ("Parent"), Enzo Acquisition Corp. and the Company
entered into an Agreement and Plan of Merger, dated as of December 19, 2003 (the
"Merger Agreement");

        WHEREAS, subject to the terms of this Amendment, the parties wish to
amend the Original Agreement in order to enable PNU and its affiliates to
continue the development of the Compound as provided herein; and

        WHEREAS, unless defined herein, capitalized terms in this Amendment
shall have the meaning set forth in the Original Agreement.

                                      Terms

        NOW THEREFORE, in consideration of the mutual covenants contained herein
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the parties hereto agree that, upon the occurrence of
the obligation of the Company to pay to Parent a Termination Fee (as defined in
the Merger Agreement) in accordance with Section 9.03(a) of the Merger
Agreement, the Original Agreement shall be amended in accordance with the
following provisions.

        1. Section 3.3 of the Original Agreement is hereby amended to read in
its entirety as follows:

           3.3 "Right of Election. Upon completion of the Company's data
analysis of Phase IIb trials in the United States for the initial indication of
the Compound, the Company shall furnish written


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notice of such completion to PNU, together with a written summary of the results
thereof and, upon PNU's written request, all written documentation reasonably
necessary for PNU to review and evaluate such data analysis and the results
thereof (such summary or documentation, as the case may be, "Documentation");
provided, however, that PNU may request and the Company shall provide PNU within
30 days, any then-existing data (to the extent available and whether or not
Phase IIb trials in the United States have then been completed) at such earlier
time as PNU shall request. PNU shall have the right to elect, upon the earlier
of (1) thirty (30) days of receipt of then-existing data (unless waived)
following its request, and (2) within ninety (90) days after receipt of
Documentation (or waiver by PNU of receipt of such data or Documentation), to
participate in the further development and/or marketing of the Compound in any
country in the world pursuant to one of the following two options:

                 (i) PNU may elect, in its sole discretion, to have the
exclusive right pursuant to a license under the Licensed PNU Patent Rights, PNU
Know-How, Company Know-How, Company Patent Rights and Assigned PNU Patent Rights
(all of the foregoing, including all inventions, discoveries and improvements
under the Control of the Company relating to each of the foregoing, the "Covered
IP") to develop, make, have made, import, use and sell, including the right to
grant sublicenses under these rights, the Licensed Products in any country in
the world. The Company covenants and agrees that for so long as there shall be a
right of election under this clause (i) the Company shall not sell, assign,
license, sublicense or otherwise transfer any of the Covered IP to any Person
other than PNU or its designated Affiliate. In the event that PNU makes any
election pursuant to this clause (i) of Section 3.3, the Company shall promptly
deliver to PNU all reasonable and customary documentation and reaffirmations
regarding such licenses as PNU shall request from time to time.

                 (ii) PNU may elect in its sole discretion not to participate in
the licensing, development or marketing of the Licensed Products with respect to
any country in the world."

        2. Section 3.4 of the Original Agreement is hereby amended to read
in its entirety as follows:

                 "3.4 Development Charges. All costs incurred by the Company in
the development of the Licensed Products, including, without limitation,
payments for clinical trials and other studies, tests and all filings and
applications and other actions necessary for achieving Governmental Approval of
the Licensed Product, shall be the sole responsibility of the Company, unless
PNU elects the option provided in clause (i) of Section 3.3, in which case all
such costs incurred with

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respect to the development of the Licensed Products after the time of such
election in the countries in the world for which such election relates shall be
the sole responsibility of PNU (unless otherwise set forth herein)."

        3. Section 3.5 of the Original Agreement is hereby amended to read in
its entirety as follows:

                 "3.5 Manufacturing. In the event that PNU elects the option
provided in clause (i) of Section 3.3, PNU shall have sole responsibility and
authority, at its cost, for the manufacture and supply of product for clinical
trial and commercial product; provided, however, that the Company shall provide
PNU, at PNU's expense, with reasonable technical assistance for the transition
of manufacturing responsibilities to PNU."

        4. Sections 4.2.1.2(i) shall be amended by inserting at the beginning of
such provision the words "Provided PNU shall not have exercised its option
provided in clause (i) of Section 3.3 as to the United States and Canada,".

        5. Section 4.2.1.2(ii) shall be amended by inserting at the beginning
thereof the words "in respect of those countries in respect of which PNU does
not exercise its option provided in clause (i) of Section 3.3."

        6. Clause (iii) of Section 4.2.1.2 shall be amended as follows:

                 "(iii) in the event PNU elects the option provided in clause
(i) of Section 3.3, PNU shall pay to the Company royalties in the amount of (A)
fifteen percent (15%) of the Net Sales by PNU and its Affiliates in the United
States and Canada, and (B) fourteen percent (14%) of the Net Sales of the
Licensed Products by PNU and its Affiliates up to the first $200,000,000 of Net
Sales in any annual period in countries outside the United States and Canada,
and twelve percent (12%) of the portion of the Net Sales of the Licensed
Products by PNU and its Affiliates which is in excess of $200,000,000 in such
annual period in countries outside the United States and Canada; and"

        7. The following new clauses (v) and (vi) shall be added to Section
4.2.1.2, after clause (iv):

                 "(v) a payment in the amount of $100,000,000 shall be made by
PNU to the Company within thirty (30) days of PNU's election of the option
provided in clause (i) of Section 3.3 as to the United States and/or Canada.



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                 (vi) in the event PNU elects the option provided in clause (i)
of Section 3.3 as to the United States and/or Canada, a milestone payment in the
amount of $100,000,000 shall be made by PNU to the Company within thirty (30)
days of a letter from the FDA granting final approval of the initial Licensed
Product."

        8. In Section 4.2.1.2, the last full unnumbered paragraph shall be
deleted.

        9. Section 6.1 of the Original Agreement is hereby amended to read in
its entirety as follows:

                 "6.1 Prosecution Obligation. The Company shall, at its sole
cost and expense, maintain during the term of this Agreement any and all
Assigned PNU Patent Rights and Company Patent Rights; it being understood and
agreed that until such time as PNU elects the option provided in clause (ii) of
Section 3.3, PNU shall have the option, in its sole discretion, to assume the
maintenance of any and all such Assigned PNU Patent Rights and Company Patent
Rights during the term of this Agreement at its sole cost and expense in any
country where such election has not been made. PNU shall, at its sole cost and
expense, apply for, and use its reasonable good faith efforts to seek issuance
of, and maintain during the term of this Agreement any and all Licensed PNU
Patent Rights, in a timely and reasonably prudent business manner until such
time as PNU elects the option provided in clause (i) of Section 3.3."

        10. Section 8.1.1 of the Original Agreement is hereby amended to delete
the third sentence in its entirety.

        11. Section 8.1.3 of the Original Agreement is hereby amended to read in
its entirety as follows:

                 "8.1.3. Each party shall have the right to defend at its own
expense all suits or proceedings seeking to have any of its Patents licensed to
the other party hereunder revoked or declared invalid; it being understood and
agreed that until such time as PNU elects the option provided in clause (ii) of
Section 3.3, PNU shall have the option, in its sole discretion, to assume any
and all such defenses regarding Covered IP in any country where such election
has not been made. If such party fails to take action in either case at least
thirty (30) days prior to the time that such party is obliged to respond to such
suit or proceeding, the other party shall have the right to take whatever action
it deems appropriate to defend such suit or proceeding. All costs and expenses
(including attorney's fees) incurred by such party in such action may be
deducted from royalties and/or other amounts otherwise payable to the other
party hereunder from the sale of the Licensed Products in the country where

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such revocation or invalidity suit or proceeding is pending, up to a maximum of
fifty percent (50%) of such royalties and/or other payments."

        12. Section 8.2.3 of the Original Agreement is hereby amended to read in
its entirety as follows:

                 "8.2.3. Notice of Claims. In the event that a claim is made
pursuant to Section 8.2.1 and 8.2.2 above against any party which seeks
indemnification hereunder (the "Indemnitee"), the Indemnitee agrees to promptly
notify the other party (the "Indemnitor") of such claim or action. In the case
of any claim by a third Person against the Indemnitee which seeks (and continues
to seek) solely monetary damages for which the Indemnitor has expressly agreed
in a written notice delivered to the Indemnitee that, as between the Indemnitor
and the Indemnitee, the Indemnitor shall be solely obligated to satisfy and
discharge the third party claim, the Indemnitor may, at its option, elect to
assume control of the defense of such claim or action; provided, however, that
(a) the Indemnitee shall be entitled to participate therein (through counsel of
its own choosing) at the Indemnitee's sole cost and expense, (b) the Indemnitor
may maintain control of the defense only for so long as the above conditions on
assumption of defense continue to be satisfied in all respects, and (c) the
Indemnitor shall not settle or compromise any such claim or action without the
prior written consent of the Indemnitee, unless such settlement or compromise
includes a general release of the Indemnitee and all of the other PNU
Indemnities or the Company Indemnities, as the case may be, from any and all
liability with respect thereto and does not impose any obligations or
restrictions on the Indemnitee and such other related parties."

        13. Section 13.3 of the Original Agreement is hereby amended to delete
the words after "not less than ninety (90) days' prior written notice to the
other party", and replace such words with a period [.].

            Except as specifically set forth above by this Amendment, the
Original Agreement shall remain in full force and effect in all respects.



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                 IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be executed as of the date first above written.



                                    ESPERION THERAPEUTICS, INC.



                                    By: /s/ Roger S. Newton
                                       ---------------------------



                                    PHARMACIA AB



                                    By: /s/
                                       ---------------------------
                                       Under Power of Attorney