AMENDMENT

                                                       [EXHIBIT 99.5.1]


                                 AMENDMENT

      AMENDMENT, dated as of May 27, 1997 (this "Amendment"), to the
 International Collaboration Agreement, effective as of June 28, 1996 (the
 "Agreement") by and between Xxxxxx-Xxxxxxx Company, a Delaware corporation
 ("Xxxxxx-Xxxxxxx"), and Pfizer Inc., a Delaware corporation ("Pfizer").
 Capitalized terms not otherwise defined herein have the meanings set forth
 in the Agreement.

      WHEREAS, Xxxxxx-Xxxxxxx has assigned certain of its rights and
 obligations under the Agreement to Xxxxxx-Xxxxxxx Export Limited, a company
 organized and existing under the laws of Ireland ("Export"), in accordance
 with the Assignment and Assumption Agreement dated as of November 1, 1996;
 and

      WHEREAS, Pfizer has assigned certain of its rights and obligations
 under the Agreement to Pfizer Overseas Inc., a corporation organized and
 existing under the laws of Delaware ("Pfizer Overseas"); and

      WHEREAS, upon this Amendment becoming effective, the parties have
 agreed that certain provisions of the Agreement be amended in the manner
 provided for in this Amendment;

      NOW, THEREFORE, the parties hereto hereby agree as follows:

                            ARTICLE I - AMENDMENTS

      SECTION 1.01.  Amendments of Section 1.01.

      (a)  The definition of "Co-Promotion Territory" in Section 1.01 of the
 Agreement is hereby amended by deleting from the second line thereof the
 country "Greece,".

      (b)  The definition of "License Territory" in Section 1.01 of the
 Agreement is hereby amended by inserting the countries "Egypt, Greece," in
 the second line thereof before the country "Iceland."

      SECTION 1.02.  Amendment of Section 3.05(a).  Section 3.05(a) is
 hereby amended by inserting the following phrase after the words "Net
 Sales" in the tenth line thereof:  "or, to the extent that XXXXXX-XXXXXXX
 packages the Products for PFIZER 30% of Net Sales,".

                         ARTICLE II - MISCELLANEOUS

      SECTION 2.01.  No Other Amendments; Confirmation.  Except as expressly
 amended, waived, modified and supplemented hereby, the provisions of the
 Agreement are and shall remain in full force and effect.

      SECTION 2.02.  Governing Law.  This Amendment shall be governed by and
 construed in accordance with the law of the State of New York other than
 those provisions governing conflicts of law.

      SECTION 2.03.  Headings.  The headings used in this Amendment have
 been inserted for convenience of reference only and do not define or limit
 the provisions hereof.

      SECTION 2.04.  Third Party Beneficiaries.  None of the provisions of
 this Amendment shall be for the benefit of or enforceable by any third
 party, including, without limitation, any creditor of either party hereto.
 No such third party shall obtain any right under any provision of this
 Amendment or shall by reason of any such provision make any claim in
 respect of any debt, liability or obligation (or otherwise) against either
 party hereto.


      IN WITNESS WHEREOF, the parties hereto, by their duly authorized
 officers, have executed this Amendment as of the date first written above.


 XXXXXX-XXXXXXX                         PFIZER OVERSEAS INC.
 EXPORT LIMITED


 By:  /s/ Xxxx X. Xxxxx                 By: /s/ Xxxxxx X. Xxxxxx
    ----------------------------           -----------------------------
    Name:  Xxxx X. Xxxxx                   Name:  Xxxxxx X. Xxxxxx
    Title: Managing Director               Title: Vice President