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                                                                     EXHIBIT 4.3

                       AMENDMENT NO. 1 TO RIGHTS AGREEMENT


This Amendment No. 1 dated November 26, 2002 ("Amendment No. 1") to the Rights
Agreement dated April 18, 2002 between Esperion Therapeutics, Inc., a Delaware
corporation (the "Company") and StockTrans, Inc., a Pennsylvania corporation, as
rights agent (the "Rights Agent") (the "Rights Agreement") is made by and
between the Company and the Rights Agent. All capitalized terms not otherwise
defined herein shall have the meanings ascribed thereto in the Agreement.

                                    RECITALS

WHEREAS, the Board of Directors of the Company has determined that it is in the
best interests of the Company to amend the Rights Agreement to modify the
definition therein of Acquiring Person to exclude a certain stockholder from
such definition under specified circumstances; and

WHEREAS, the Company has determined to amend the Rights Agreement in accordance
with Section 27 of the Rights Agreement and the Rights Agent is directed to join
in this Amendment No. 1 to the Rights Agreement as set forth herein.


                                    AGREEMENT

NOW THEREFORE, the parties hereto, intending to be legally bound, hereby agree
as follows:

1. The definition of Acquiring Person in Section 1 of the Rights Agreement is
hereby amended to read in its entirety as follows:

                  "Acquiring Person" shall mean any Person who or which,
together with all Affiliates and Associates of such Person, shall be the
Beneficial Owner of 15% or more of the Common Shares then outstanding, but shall
not include the Company, any Subsidiary of the Company, any employee benefit
plan of the Company or of any Subsidiary of the Company, any Person or entity
organized, appointed or established by the Company for or pursuant to the terms
of any such plan. Notwithstanding the foregoing, no Person shall become an
"Acquiring Person" as the result of an acquisition of Common Shares by the
Company which, by reducing the number of Common Shares outstanding, increases
the proportionate number of Common Shares beneficially owned by such Person to
15% or more of the Common Shares then outstanding; provided, however, that if a
Person shall become the Beneficial Owner of 15% or more of the then outstanding
Common Shares by reason of Common Shares purchased by the Company and shall,
after the Company announces such share purchases, become the Beneficial Owner of
any additional Common Shares, then such Person shall be deemed to be an
"Acquiring Person." Notwithstanding the foregoing, if a majority of the Board of
Directors determines in good faith that a Person who would otherwise be an
"Acquiring Person," as defined pursuant to the foregoing provisions of this
paragraph, has become such inadvertently and without any intention of changing
or influencing control of the Company, and such Person divests as promptly as
practicable after being advised of such determination a sufficient number of
Common Shares so that such Person would no longer be an "Acquiring Person," as
defined pursuant to the foregoing



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provisions of this paragraph, then such Person shall not be deemed to be an
"Acquiring Person" for purposes of this Agreement. Notwithstanding anything to
the contrary contained in this definition, Scott Sacane ("Sacane"), managing
member of Durus Capital Management, LLC ("Durus") and portfolio manager of
Perseus, LLC ("Perseus"), together with Durus and Perseus (with Sacane, Durus
and Perseus referred to herein as the "Sacane Group") shall not be deemed to be
an "Acquiring Person" unless and until the earlier of such time as the Sacane
Group, together with all Affiliates and Associates, directly or indirectly,
becomes the Beneficial Owner of 25% or more of the Common Shares then
outstanding or ceases to hold any of the Common Shares of which it is the
Beneficial Owner without any intention of changing or influencing control of the
Company;

Except as amended hereby, the Rights Agreement remains in full force and effect.

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 by
their duly authorized representatives effective the date set forth above.



ESPERION THERAPEUTICS, INC.                   STOCKTRANS, INC.



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

Name:  Roger S. Newton                        Name:  Gina Hardin
       ------------------------------------          ---------------------------

Title:  President & Chief Executive Officer   Title:  Vice President
        -----------------------------------           --------------------------

         Duly Authorized                               Duly Authorized

Date:  November 26, 2002                      Date:  November 26, 2002
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