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                                                                   EXHIBIT 10.21


                        CONFIDENTIAL TREATMENT REQUESTED

Confidential Portions Of This Agreement Which Have Been Redacted Are Marked With
    Brackets ("[****]"). The Omitted Material Has Been Filed Separately With
                    The Securities And Exchange Commission.

                      Amendment to Collaboration Agreement


                                                                     May 3, 2000



Donald L. Barbeau
President
Inpharmakon Corporation
191 Waukegan Avenue
Suite 206
Northfield, Illinois 60099


Dear Donald,

This letter records the terms on which First Horizon Pharmaceutical Corporation
(formerly Horizon Pharmaceutical Corporation) ("First Horizon") and Inpharmakon
Corporation ("Inpharmakon") have agreed to settle their differences with regard
to certain issues arising out of their Collaboration Agreement made as of
October 31, 1998 ("Collaboration Agreement").

1.   First Horizon shall pay to Inpharmakon a total of $200,000 (the "IPO
     Payment") within 30 days of the closing of First Horizon's initial public
     offering of its shares of Common Stock ("IPO"); provided, however, that in
     the event that the IPO has not closed by October 20, 2000, First Horizon
     shall pay to Inpharmakon one half of the IPO Payment ($100,000) on October
     20, 2000 and provided further, that in the event that the IPO has not
     closed by April 20, 2001, First Horizon shall pay to Inpharmakon the
     remaining balance of the IPO Payment ($100,000) on April 20, 2001. For the
     purposes of this paragraph "closing" of the IPO refers to the date on which
     First Horizon's underwriters fund the purchase of IPO shares from First
     Horizon. The IPO is a firm commitment underwriting.

2.   Secondly the Collaboration Agreement is amended to provide for the
     following additional compensation:

     a.   First Horizon shall pay to Inpharmakon a total of $[****], in place of
          the $[****] payment required by Section 4.01(ii) of the Collaboration
          Agreement, such payment to be made on the earlier to occur of (i)
          within 30 days after the filing of the NDA for the Product for the
          Indication by First Horizon, and (ii) December 31, 2001.

     b.   First Horizon shall pay to Inpharmakon a total of $[****], in place of
          the payment of $[****] required by Section 4.01(iii) of the
          Collaboration Agreement, within 30 days after the approval of such
          NDA.

3.   Subsections 8.04(iii) and (iv) of the Collaboration Agreement are deleted.

4.   In order to avoid future misunderstandings and to foster a closer spirit of
     collaboration, First Horizon will designate Mr. Ralph Jordan, or such other
     individual as First Horizon may designate


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     from time to time as Project Liaison between Inpharmakon and First Horizon
     as the individual to whom Inpharmakon may direct all questions and
     inquiries regarding the development of, and FDA registration activities
     concerning, the Product. In addition First Horizon agrees to provide
     Inpharmakon with detailed written quarterly reports to be delivered to
     Inpharmakon within 30 days after the end of each quarter during the term of
     the Collaboration Agreement, such reports to include but not be limited to
     a reasonable explanation of the progress of and any changes in Horizon's
     regulatory strategies for the Product. In addition to the foregoing and as
     part of its undertaking hereunder, First Horizon will provide Inpharmakon
     with (a) at the same time as the FDA, the summary sections of any IND, New
     Drug Application (whether full, partial or abbreviated) and amendments
     thereto, excluding attachments, filed for the Product with the FDA until
     such time as the FDA has approved the NDA, and (b) copies of all other
     written communications to or from the FDA concerning the Product, including
     but not limited to correspondence, filings, minutes of meetings, briefing
     documents, responses to and from the FDA, and supporting documentation
     whether in printed or electronic form. First Horizon agrees to make
     available to Inpharmakon knowledgeable personnel with the knowledge and
     authority to discuss all such activities and to give Inpharmakon access in
     Horizon's offices, at no cost to First Horizon, to the attachments to
     Horizon's filings for the Product with the FDA on not less than 48 hours
     notice to Horizon.

5.   Provided that First Horizon makes the payments in accordance with the
     provisions of the above Paragraphs 1 and 2, each of Inpharmakon and First
     Horizon shall and does hereby remise, release and forever discharge and, by
     these presents, does, for itself, its directors, officers, agents,
     successors, assigns, employees and representatives and each of them,
     release and forever discharge the other party and its directors, officers,
     agents, successors, assigns employees and representatives, and each of
     them, from and against all manner of actions, complaints, causes of action,
     claims, suits, debts, breaches, sums of money, accounts, reckonings,
     contracts, torts, controversies, agreements, promises, damages, judgments,
     executions, claims and demands whatsoever in law or in equity arising out
     of, directly or indirectly, any matter, transaction, representation, event
     or thing from the first day in time to and including the date of this
     letter, including, but without limitation, any and all previously
     unreleased and/or unfulfilled obligations of either party arising under or
     pursuant to the Collaboration Agreement.

6.   As a material inducement to Inpharmakon agreeing to the terms and
     conditions of this letter, First Horizon hereby represents and warrants to
     Inpharmakon that (a) the only formulation for the Product that it is now
     being developed is for the Indication; (b) it will promptly inform Horizon
     in the event it abandons such formulation or does or causes others to do
     any work on any other formulation for communications through the date of
     this letter to or from the FDA concerning the Product, (c) it has provided
     Inpharmakon with true copies of all written communications through the date
     of this letter to or from the FDA concerning the Product, including but not
     limited to correspondence, filings, minutes of meetings, briefing
     documents, responses to and from the FDA, and supporting documentation
     whether in printed or electronic form; (d) the attached amendment to the
     Product Development and Supply Agreement entered into as of March 25, 1999
     by and between Penwest Pharmaceuticals Co. ("Penwest") and First Horizon
     (the "Penwest Agreement") is a true and correct copy of an amendment to the
     Penwest Agreement executed by the parties thereto on May 3, 2000, which
     amendment is in full force and effect, and (e) it will not further amend
     the assignment provisions of the Penwest Agreement without Inpharmakon's
     prior written consent which consent will not be unreasonably withheld.

7.   In the event of a material breach or material default by First Horizon
     under the representations and warranties contained in Paragraph 6 above,
     Inpharmakon may give notice of termination to First Horizon specifying the
     breach or default, in which event the Collaboration Agreement shall
     terminate immediately if the breach or default is not capable of cure, or,
     if the breach or default is capable of cure, after 30 days unless First
     Horizon cures the breach or default within the 30 day period. In the event
     that the Collaboration Agreement is terminated pursuant to Inpharmakon's
     notice hereunder, Inpharmakon shall have the exclusive right to proceed
     with a NDA for the Product for the Indication using the Formulation and the
     data from the Clinical Trials as has been
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         acquired or developed by Horizon at the date of termination, and shall
         have the right to assume Horizon's rights to the same and the NDA, if
         applicable, without cost to Inpharmakon or Inpharmakon Affiliates. In
         that event Horizon shall release to Inpharmakon its rights to the
         Opportunity Package, the Formulation, the related not publicly
         available information provided by Inpharmakon or developed by or for
         Horizon, and registration data related to the NDA for the Product for
         the Indication.

8.       In the event that First Horizon grants Penwest a sublicense
         under the provisions of Section 11.4 of the Penwest Agreement or
         otherwise to the Horizon Test and Regulatory Data (as defined in the
         Penwest Agreement), Horizon agrees to pay to Inpharmakon the royalties
         provided under the provisions of Section 4.02 of the Collaboration
         Agreement whether or not the Collaboration Agreement is still in force
         provided that the Collaboration Agreement is not terminated by First
         Horizon under Section 8.02 of the Collaboration Agreement in which
         case the right to such royalties would terminate with the Collaboration
         Agreement.

9.       Defined Terms used in this letter have the same meaning as
         they have in the Collaboration Agreement.

10.      All other provisions of the Collaboration Agreement will
         continue in full force and effect except to the extent changed by the
         provisions of this letter.

11.      The parties agree to execute a formal amendment to the
         Collaboration Agreement within 30 days of the date of this letter
         incorporating the above provisions into the Collaboration Agreement. At
         such time as that amendment has been executed and exchanged by the
         parties, the amendment will replace the agreement contained in this
         letter.

12.      This letter agreement may be executed in one or more counterparts, each
         of which shall be an original, but all of which taken together shall
         constitute one and the same agreement.

If the above terms and conditions accurately record our agreement, please sign
and return the acknowledgement at the foot of this letter.


Sincerely,

                                                   AGREED & ACCEPTED
/s/ William G. Campbell                            Inpharmakon Corporation
William G. Campbell
Controller
                                                   /s/ Donald L. Barbeau

                                                   Donald L. Barbeau
                                                   President


cc.      Christopher R. Manning (Burke, Warren, MacKay & Serritella)
         Michael J. Hogg (Business Counsel)