<PAGE>   1
March 20, 1995


                                                                    CONFIDENTIAL
                                                             VIA FEDERAL EXPRESS

Dr. Paul Litka
305 Farwood Road
Wynnewood, PA  19096

Dear Paul:

I am pleased to offer you the position of Vice President, Clinical Research with
Magainin Pharmaceuticals Inc., reporting to Dr. Leonard Jacob, Executive Vice
President and Chief Operating Officer of the Company. The base salary for this
position will be $12,500 per month ($150,000/year). Contingent upon your
acceptance of this offer, it is expected that the Compensation Committee of the
Board of Directors will grant to you at its next meeting options to purchase
40,000 shares of Magainin common stock, exercisable at the fair market value of
the underlying common stock on the date of such meeting. These options will have
a term of 10 years and vest at the rate of 25% per year beginning on the first
anniversary of the date of your commencement of employment. As with all Magainin
options, the grant will be subject to execution of a stock option agreement in
the form specified by the Compensation Committee. A copy of our Stock Option
Plan is attached hereto. Additionally, you will be eligible to participate in
any Cash Bonus Plan which might be approved by the Company's Senior Management
and Board of Directors.

If your employment is terminated without cause, you will receive your monthly
base salary for six (6) months following the date of termination, or for such
shorter period until you have secured employment elsewhere.

Magainin may have already provided you with certain of its confidential business
or scientific information which it expects you to keep confidential and to use
only to further Magainin's legitimate business interests. If you have not
already signed an agreement to keep Magainin's business and scientific
information confidential, you will be asked to do so at the start of your
employment, and a copy of that agreement is enclosed. Just as Magainin expects
you to keep confidential its business or scientific information, Magainin also
expects you to honor your obligations to your former employers with respect to
maintaining the confidentiality of their business or scientific information.
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Dr. Paul Litka
March 20, 1995
Page 2



In addition to the confidentiality agreement, you will be subject to such other
obligations as employees of our Company may be subject. In addition, you will be
eligible for our benefits package available to all employees. This package for
you will be supplemented to include an aggregate of twenty (20) vacation days
per year, in addition to two (2) personal days. Enclosed is a summary of other
benefits.

We look forward to your joining us at Magainin Pharmaceuticals Inc. Please
indicate acceptance of this offer, which is for at will employment, by your
signature below. Please also indicate a mutually agreeable start date and return
it to me using the enclosed Federal Express mailer at your earliest convenience.
This offer of employment will remain in effect until Thursday, March 30, 1995.
If you have any questions, please do not hesitate to call myself or Dr. Jacob.

Sincerely yours,

/s/ Michael R. Dougherty
--------------------------------
Michael R. Dougherty
Senior Vice President and
 Chief Financial Officer



Accepted:    /s/ Paul Litka                            Date:    March 24, 1995
          ------------------------                          -------------------
            Dr. Paul Litka


Starting Date:   April 3, 1995
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cc:  L. Jacob

MRD:mk