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                                                                   EXHIBIT 10.75


                     FIFTH AMENDMENT TO CONSULTING AGREEMENT

         This FIFTH AMENDMENT TO CONSULTING AGREEMENT (the "Amendment") is made
as of the 1st day of January 2001 (the "Effective Date"), by and between JOHN M.
PIETRUSKI, an individual residing at 27 Paddock Lane, Colts Neck, New Jersey
07722 ("Consultant"), and TEXAS BIOTECHNOLOGY CORPORATION, a Delaware
corporation located at 7000 Fannin Street, Suite 1920, Houston, Texas 77030 (the
"Corporation").

         WHEREAS, the Corporation and Consultant have entered into that certain
Consulting Agreement, dated January 1, 1992 (the "Agreement"), as set forth in
Exhibit "A" attached hereto and incorporated herein by reference; and

         WHEREAS, pursuant to the Agreement, the Corporation has retained
Consultant to provide consulting services to the Corporation with respect to
corporate governance, business development and other such matters; and

         WHEREAS, the Corporation and Consultant desire to amend the Agreement
as herein set forth.

         NOW, THEREFORE, for and in consideration of the foregoing and of the
mutual covenants contained herein, the parties hereto agree as follows:

         1. Definitions. If not otherwise defined herein, all capitalized terms
used herein shall have their respective meaning assigned to them in the
Agreement.

         2. Amendment to Section 2. Effective as of the date hereof, Section 2
of the Agreement is hereby amended by deleting paragraph (a) in its entirety and
substituting the following in lieu thereof:

                  "(a) Consultant's retention under this agreement shall
         commence on the date hereof (the "Commencement Date") and shall end on
         the earliest of: (i) the death or disability (as defined herein) of
         Consultant; (ii) the termination of Consultant's retention by the
         Corporation for cause (as defined herein); or (iii) two years after the
         Effective Date. After the expiration of such two-year period, this
         Agreement may be renewed for additional periods on all the remaining
         terms and conditions set forth herein upon mutual agreement of
         Consultant and the Corporation."

         3. The terms and provisions set forth in this Amendment shall modify
and supersede all inconsistent terms and provisions set forth in the Agreement
and except as expressly modified and superseded by this Amendment, the terms and
provisions of the Agreement are ratified and confirmed and shall continue in
full force and effect. Corporation and Consultant agree that the Agreement as
amended shall continue to be legal, valid, binding and enforceable in accordance
with its terms.


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         4. Except as expressly modified or amended hereby, the terms and
provisions of the Agreement shall remain in force and effect in accordance with
the terms hereof; provided, however, that from and after the date hereof any
reference to the Agreement shall be deemed and construed as meaning the
Agreement as amended and modified hereby.

         IN WITNESS WHEREOF, the parties have executed this Amendment as of the
day and year first written above.

                                CONSULTANT:

                                /s/ John M. Pietruski
                                -------------------------------
                                John M. Pietruski



                                CORPORATION:

                                TEXAS BIOTECHNOLOGY CORPORATION

                                /s/ David B. McWilliams
                                ---------------------------------
                                David B. McWilliams
                                President and Chief Executive Officer