<PAGE>   1
                                 SECOND ADDENDUM


         Magainin Pharmaceuticals ("Magainin") and Abbott Laboratories
("Abbott") entered into a Purchase Order Agreement for Phase IV dated October 6,
1995 (the "Purchase Order") wherein Abbott is to perform certain activities
relating to Magainin's Bulk Product, as defined in the Purchase Order.

         The Purchase Order was amended on May 8, 1996.

         Magainin and Abbott desire to further amend the Purchase Order as
follows:

         1.       Abbott shall produce three (3) additional 1-kilogram batches
                  of bulk MSI-78. As previously discussed, the pricing and
                  payment schedule for each individual 1-kilogram batch will be
                  as follows:

<TABLE>
<CAPTION>
          QUALIFICATION RUNS                         PRICE                          PAYMENT
          ------------------                         -----                          -------
<S>                                                 <C>                             <C>  
          First 1-Kilogram Batch                     $[***********]                 April-July 1997*
          Second 1-Kilogram Batch                    $[***********]                 Upon Delivery of
                                                                                    the Second 4.5
                                                                                    Kilogram
                                                                                    Qualification Run
          Third 1-Kilogram Batch                     $[***********]                 Upon Delivery of
                                                                                    the Third 4.5
                                                                                    Kilogram
                                                                                    Qualification Run
                               TOTAL                 $[***********]

                                                    *$[***********] per month
</TABLE>

      2.  Abbott shall provide additional analytical services as described in
          Attachment A to this Second Addendum. Magainin shall pay Abbott
          $[*******] per month, beginning October 1996 and will continue to be
          billed at the $[*******]/month rate through the end of May 1997. See
          Attachment A for the activities executed in the Additional Analytical
          Services Program.

      3.  All payments hereunder shall be made by the last day of each calendar 
          month.

      4.  Abbott shall make the following qualification runs in lieu of the 
          qualification runs set forth in the Purchase Order; three (3) one (1)
          kilogram qualification runs and three

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<PAGE>   2


      (3) qualification runs manufactured at a 4.5 kilogram scale, to be
      delivered on dates mutually agreed to by Magainin and Abbott.


      5.  Upon completion of the third 4.5 kilogram qualification run, a final
          scale-up qualification run will be executed. This run is projected to
          be produced at a 9 to 13.5 kilogram scale. The final decision
          regarding the size of this run will be based on a mutual agreement
          between Magainin and Abbott after review of the data available from
          previous runs. Pricing for this final scale-up qualification run will
          be $[***] per gram.

      6.  Abbott shall use its reasonable best efforts to ensure that the Drug
          Master File for Bulk Drug Substance will be ready for submission to
          the FDA (some of which qualification runs shall have less than six (6)
          months stability data, in the fourth (4) quarter of 1997.

      7.  All other provisions of the Purchase Order, as amended, are hereby 
          ratified and confirmed.

      IN WITNESS WHEREOF, the parties have executed this Second Addendum by
their duly authorized representatives as of the later date set forth below.

MAGAININ PHARMACEUTICALS INC.                  ABBOTT LABORATORIES



By:    /s/ Michael R. Dougherty                By: /s/ Chris M. Kolber
       ----------------------------                -----------------------------

Title: Executive Vice President and            Title: Vice President of 
       ----------------------------                   --------------------------
       Chief Financial Officer                        Commercial Operations
       ----------------------------                   --------------------------

Date: May 7, 1997                              Date: May 12, 1997
      -----------------------------                  ---------------------------






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                                  ATTACHMENT A
                    ADDITIONAL ANALYTICAL ACTIVITIES PROGRAM

PURPOSE: To develop and execute a program, which will characterize impurities
relative to MSI-78. This program has evolved out of the August 1996 request by
the FDA that displays "a reasonable best effort" towards impurity
identification.

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I.
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II.
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III.
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IV.
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V.
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VI.
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VII.
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