Document:

<PAGE>   1
                                                                  Exhibit 10.24A

* Certain information on all pages have been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

[ASTRAZENECA LETTERHEAD]

Leland Wilson, President                                       December 22, 1999
VIVUS International Ltd.
c/o VIVUS Inc.
605 E. Fairchild Drive
MOUNTAIN VIEW, CA 94043
USA

RE. DISTRIBUTION AGREEMENT ENTERED INTO BY AND BETWEEN ASTRA AB ("ASTRA") AND
VIVUS INTERNATIONAL LTD. ("VIVUS") ON MAY 29, 1996 (THE "AGREEMENT")

Dear Sirs,

(All terms defined in the Agreement and used herein with capital letters shall
have the meaning provided for in the Agreement.)

I write to you to acknowledge the following agreement reached between ASTRA and
VIVUS regarding the settlement of any claims pursuant to or relating to the
Agreement;

(i) ASTRA shall pay to VIVUS no later than January 31, 2000 the amount of [*].
Such amount shall be the full payment for any financial obligation on ASTRA,
not already as of this date fulfilled by ASTRA, to VIVUS pursuant to or in
relation to the Agreement, incurred as of this date or hereafter. As a
consideration for such payment ASTRA shall have the right to have any quantity
of PRODUCT manufactured by VIVUS, and held in stock for ASTRA as of this date,
delivered to ASTRA without any requirement on ASTRA to make any further payment
for such delivery. The parties acknowledge that the quantity of PRODUCT
currently manufactured and kept in stock for ASTRA amounts to [*].

(ii) Subject to the payment under (i) being made, the parties agree, effective
also during the period starting on the date of this letter and until the date
of such payment, to the following. ASTRA and VIVUS withdraw any financial
claims pursuant to or in relation to the Agreement and the parties shall have
no financial claims or obligations in relation to each other pursuant to or in

<PAGE>   2
[AstraZeneca LOGO]

Leland Wilson, President                                    December 22, 1999

relation to the Agreement incurred as of this date or hereafter. ASTRA's right
to have PRODUCT delivered according to (i) shall, however, survive until such
delivery has been made in full and further the parties responsibilities
regarding product liability in accordance with Sections 13.3 and 13.4 of the
Agreement shall apply in accordance with what is stated therein.

Consequently VIVUS withdraws any claim and allegation stated in its notice of
default of December 16, 1999, and the parties will not as a consequence of such
VIVUS' letter enter into any particular procedure for resolution of issues laid
down in the Agreement. The parties will not regarding any issue contemplated in
the settlement under (i) and this (ii) make any claims, take any legal action
or seek any remedy provided for under the Agreement or otherwise, other than in
order to enforce its rights in accordance with what is stated in this letter.

(iii) The parties acknowledge that ASTRA may at its discretion continue to
sell, but with no performance obligation or obligation to market or otherwise
support the promotion of, the PRODUCT in certain countries of the TERRITORY
during a period of time to be defined in detail by the parties but basically to
expire no later than [*]

(iv) The parties agree that what is stated under (i) and (ii) shall not prevent
that either party may be entitled to get reimbursed for minor costs not to
exceed one hundred thousand dollars ($100,000) appropriate and provided for in
the Agreement directly connected to the handback of distribution of the PRODUCT
pursuant to the reversion of rights to the PRODUCT under the Agreement.

(v) The parties acknowledge that the Agreement, pursuant to ASTRA's
discontinuance to sell the PRODUCT, substantially lacks content and that the
parties shall use their best reasonable efforts to amicably settle any
outstanding issues not included in the settlement mentioned above under (i) and
(ii), thereby formally terminating the Agreement.

                                      2(3)
<PAGE>   3
[ASTRAZENECA LOGO]

Leland Wilson, President                                    December 22, 1999

I would appreciate your approval to the above by signing the attached copy of
this letter and return it to me. This letter has been sent also by fax and I
would therefore appreciate your signed fax copy in return by fax as well.

Yours sincerely,

ASTRA AB
(publ)

/s/ John Patterson

John Patterson, FRCP FFPM
Executive Vice President
Product Strategy & Licensing

cc.  Wilson, Sonsini, Goodrich & Rosati
     650 Page Mill Road
     Palo Alto, CA 94304-1050
     USA

                                        Approved:

                                        Date:
                                        VIVUS International Ltd.

                                        _________________________________
                                        Leland Wilson,
                                        President

                                      3(3)<PAGE>   1
                                                                   EXHIBIT 10.38

*CERTAIN INFORMATION ON ALL PAGES HAVE BEEN OMITTED AND FILED
SEPARATELY WITH THE COMMISSION. CONFIDENTIAL TREATMENT HAS
BEEN REQUESTED WITH RESPECT TO THE OMITTED PORTIONS.

                               LICENSE AGREEMENT

     THIS LICENSE AGREEMENT (the "Agreement"), effective as of February 29, 2000
(the "Effective Date"), is by and between ASIVI, LLC, a Delaware limited
liability company, with offices at 1172 Castro Street, Mountain View, California
94040 ("ASIVI"), and VIVUS, INC., a Delaware corporation with a principal place
of business at 1172 Castro Street, Mountain View, California 94040 ("VI").

                                   BACKGROUND

     A. ASIVI owns certain Patent Rights (as defined below) relating to, inter
alia, the design, development, manufacture and use of products containing
prostaglandin E and/or other vasodilators for the treatment of female sexual
dysfunction ("FSD"); and

     B. VI desires to obtain an exclusive license under the ASIVI Technology (as
defined below) to develop and commercialize Products (as defined below) for the
diagnosis, prophylaxis and treatment of FSD, and ASIVI desires to grant such a
license to VI, on the terms and conditions herein.

     NOW, THEREFORE, in consideration of the mutual covenants and undertakings
set out herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, ASIVI and VI agree as follows:

1. DEFINITIONS

          1.1 "Affiliate" shall mean any corporation or other entity which
       controls, is controlled by or is under common control with VI. For
       purposes of this definition only, "control" shall mean ownership or
       control, directly or indirectly, of more than fifty percent (50%) of the
       shares or other rights of the subject entity entitled to vote in the
       election of directors (or, in the case of an entity that is not a
       corporation, to the election of the corresponding managing authority).

          1.2 "ASI" shall mean AndroSolutions, Inc., a Tennessee corporation
       located at 200 Fort Sanders West Blvd., Suite 309, Knoxville, TN 37922.

          1.3 "ASI Product Formulation" shall mean a Product formulation listed
       on Exhibit 1.3. The optimum proportions of the excipients in the ASI
       Product Formulation may be altered as Product development progresses and
       will not result in reclassification of the Product formulation.

          1.4 "Commercially Reasonable Efforts" shall, with respect to a
       Product, mean efforts and resources equivalent to those normally employed
       by entities in the biopharmaceutical marketplace, substantially
       comparable to VI, to develop, manufacture, market or sell a product of
       similar market potential at a similar stage in its product life, taking
       into account for example the establishment of the Product in the
       marketplace, the competitiveness of alternative products, the proprietary
       position of the Product, the likelihood of regulatory approval, including
       consideration of safety and efficacy, for the Product given the
       regulatory authority and structure involved, the profitability of the
       Product and VI's available resources. Commercially Reasonable Efforts
       shall be determined on a market-by-market basis for each Product.
<PAGE>   2
     1.5.  "Confidential Information" shall have the meaning specified in that
certain Confidentiality and Non-Disclosure Agreement, dated December 16, 1999,
by and between ASI, VI and ASIVI.

     1.6.  "Control" or "Controlled" shall mean possession of the ability to
grant a license or sublicense as provided for herein, without violating the
terms of any agreement or other arrangement with any third party.

     1.7.  "FDA" shall mean the U.S. Food and Drug Administration, or any
successor agency.

     1.8.  "FSD IP" shall mean the patent rights, including issued patents
and/or pending patent applications, relating to, inter alia, the design,
development, manufacture, and use of products containing prostaglandin E and/or
other vasodilators for the treatment of FSD that will be assigned to ASIVI
pursuant to (a) the Assignment Agreement executed by ASI, and (b) the
Assignment Agreement executed by VI, each dated the date hereof.

     1.9.  "First Commercial Sale" shall mean, with respect to each Product in
each country, the first bona fide commercial sale of such Product in such
country by or under authority of VI.

     1.10. "ASIVI Technology" shall mean the Know How and Patent Rights, in
each case that are Controlled by ASIVI during the term of this Agreement.

          1.10.1    "Know How" shall mean the Confidential Information owned or
          Controlled by ASIVI as of the Effective Date and made available to VI
          by ASIVI necessary for the exercise of the Patent Rights, including
          technical data, protocols and methods. For the avoidance of doubt,
          the Know How does not include any Patent Rights.

          1.10.2    "Patent Rights" shall mean all United States and foreign
          patents (including all reissues, extensions, substitutions,
          re-examinations, supplementary protection certificates and the like,
          and patents of addition) and patent applications (including, without
          limitation, all continuations, continuations-in-part and divisions
          thereof) owned or Controlled by ASIVI, in each case, which claim an
          invention that is necessary to develop, produce, make, have made,
          import, have imported, export, have exported, use, offer for sale and
          sell Products, in each case that are Controlled by ASIVI during the
          term of this Agreement.

     1.11.     "Marketing Approval" shall mean, with respect to each country
for a particular Product, approval of the MAA filed in such country by the FDA,
or the health regulatory authority in such country that is the counterpart of
the FDA.

     1.12.     "Marketing Approval Application" or "MAA" shall mean a New Drug
Application ("NDA"), Premarket Approval ("PMA") application, Premarket
Notification (510(k)) application, Product Licensure Approval (PLA)
application, Biologics Licensure Approval (BLA) application, or other similar
regulatory filings as required under the United States Federal Food, Drug and
Cosmetics Act and the regulations promulgated thereunder, or a comparable
filing for Marketing Approval in a country for the manufacture, use or sale of
a Product in that country.

     1.13.     "Net Sales" shall mean the amount invoiced by VI or its
Affiliates or its Sublicensees (for purposes of this definition, as applicable,
the "Selling Party") for the sale of Products to bona

                                      -2-
<PAGE>   3
fide independent third parties throughout the world, less (i) ordinary and
customary trade discounts actually allowed by the Selling Party to the third
party purchaser; (ii) credits, rebates and returns allowed and credited to the
third party purchaser (including, but not limited to, wholesaler and retailer
returns); (iii) freight, handling and duties paid on shipments by the Selling
Party to the third party purchaser and separately identified on the invoice; and
(iv) sales taxes, excise taxes, consumption taxes, customs duties and other
compulsory payments to governmental authorities actually paid with respect to
the sale by the Selling Party to the third party purchaser. For the avoidance of
doubt, Net Sales shall not include sales by a Selling Party to its Affiliates or
Sublicensees for resale; provided, however, that if the Selling Party sells a
Product to an Affiliate or Sublicensee for resale, Net Sales shall include the
amounts invoiced by such Affiliate or Sublicensee to third parties on the resale
of such Product.

Net Sales, as defined herein, also includes any and all non-cash consideration
received by VI, and VI's Affiliates and Sublicensees, from sublicensing,
marketing, promotion, use, distribution, sale or other disposal of the Products,
excluding the distribution of Products for use in research and/or development,
in clinical trials or as promotional samples. All non-cash consideration will be
valued at the fair market value thereof established by agreement of the parties
or, failing that, by a qualified independent accountant approved by ASIVI and
VI. ASIVI will bear the cost of such accountant.

In the case of discounts on "bundles" of products or services which include
Products, Net Sales will be calculated by discounting the bona fide list price
of such Product by the average percentage discount of all products of VI and/or
its Sublicensees in a particular "bundle," calculated as follows:

Average percentage discount on a particular bundle = (1 - A/B) x 100

where A equals the total discounted price of a particular "bundle" of products,
and B equals the sum of the undiscounted bona fide list prices of each unit of
every product in such "bundle." VI shall provide ASIVI documentation, reasonably
acceptable to ASIVI, establishing such average discount with respect to each
"bundle." If VI cannot so establish the average discount of a "bundle," Net
Sales shall be based on the undiscounted list price of the Products in the
"bundle." If a Product in a "bundle" is not sold separately and no bona fide
list price exists for such Product, the parties shall negotiate in good faith an
imputed list price for such Product, and Net Sales with respect thereto shall be
based on such imputed list price.

     1.14.  "Phase II" and "Phase III" shall mean Phase II, and Phase III
clinical trials, respectively, in each case as prescribed by the U.S. Food and
Drug Administration or a corresponding foreign entity.

     1.15.  "Product" shall mean any product containing prostaglandin E and/or
other vasodilators for the treatment of FSD covered by the FSD IP.

          1.15.1  "Initial Product" shall mean the Product which is selected
for Phase III clinical trials as defined in Section 3.2.3.

     1.16.  "Sublicensee" shall mean a third party to whom VI has granted a
license or sublicense pursuant to Section 2.2 hereof.

                                      -3-
<PAGE>   4
          1.17.  "Valid Claim" means (i) a claim of an issued and unexpired
     patent included within the Patent Rights which has not been held
     unenforceable or invalid by a court or other governmental agency of
     competent jurisdiction, and which has not been disclaimed or admitted to be
     invalid or unenforceable through reissue or otherwise, or (ii) a claim of a
     pending patent application within the Patent Rights.

          1.18. "VI Product Formulation" shall mean a Product formulation listed
     on Exhibit 1.18. The optimum proportions of the excipients in the VI
     Product Formulation may be altered as Product development progresses and
     will not result in reclassification of the Product formulation.

2. LICENSE

          2.1.  Grant of Rights to VI.  Subject to the terms and conditions of
     this Agreement, ASIVI hereby grants to VI and VI's Affiliates an exclusive
     [subject to the rights granted under Section 11.6 of that certain LLC
     Agreement of ASIVI dated February 29, 2000], worldwide right and license
     under the ASIVI Technology to make, have made, import, have imported,
     export, have exported, use, sell, have sold, offer for sale Products,
     practice any method, process or procedure and otherwise exploit the ASIVI
     Technology.

          2.2.  Sublicenses.  The license granted under Section 2.1 above shall
     include the right to grant and authorize sublicenses under the ASIVI
     Technology to make, have made, import, have imported, export, have
     exported, use, sell, have sold, offer for sale Products, practice any
     method, process or procedure and otherwise exploit the ASIVI Technology. VI
     shall use all commercially reasonable efforts to cause each of its
     Sublicensees, if any, to purchase either (i) its requirements for Products
     from VI, or (ii) [*]

3. RESEARCH AND DEVELOPMENT

          3.1.  Regulatory Matters.  VI shall use Commercially Reasonable
     Efforts to develop and commercialize Products, including (i) the
     preparation and filing of all MAAs, and (ii) carrying out and completing
     all associated activities, including design and management of clinical
     trials, in each case up to and including Marketing Approval, and shall
     thereafter maintain such approval. VI shall be the record holder of such
     Marketing Approval. VI shall also obtain any export approvals required by
     the FDA to export Products to other countries. ASIVI shall provide VI with
     a copy of any data that are within ASIVI's possession and Control and are
     necessary to file an MAA in a particular country.

          3.2.  Initial Product Development.  The formulation of the Initial
     Product under this Agreement shall be determined as follows:

               [*]

                                      -4-
<PAGE>   5
               3.2.2.    Phase II Clinical Trials. VI shall conduct Phase II
          clinical trials based on the results of the analysis set forth in
          Section 3.2.1 above, wherein both an ASI Product Formulation and a VI
          Product Formulation shall be tested. Such Phase II clinical trials may
          be conducted with only one (1) candidate Product formulation upon
          agreement between VI and ASI.

               3.2.3.    Phase III Clinical Trials. Based on the final results
          of the Phase II studies set forth in Section 3.2.2 above, VI and ASI
          will select the Initial Product formulation, if any, for Phase III
          studies. To the extent that the parties disagree with respect to the
          Product formulation to be selected for the Phase III clinical trial,
          such dispute will be settled according to Article 9.

4.   PAYMENTS

          4.1. Milestone Payments. VI agrees to make the following payments to
     ASIVI, in connection with the Initial Product only, upon the occurrence of
     each milestone specified below:

<TABLE>
<CAPTION>
               MILESTONES                                        PAYMENT
-------------------------------------------------------------------------------
<S>                                                             <C>
[*]                                                              [ * ]
-------------------------------------------------------------------------------
[*]                                                              [ * ]
-------------------------------------------------------------------------------
[*]                                                              [ * ]
-------------------------------------------------------------------------------
</TABLE>

          4.1.1. Milestones for Other Products. ASIVI and VI shall negotiate in
     good faith with ASI additional milestone payments, if any, for any Products
     other than the Initial Product subjected to the Phase III clinical trial
     set forth in Section 3.2.3.

          4.1.2. Payment. The payments set forth in this Section 4.1 shall each
     be due and payable within thirty (30) days after the occurrence of the
     milestone event. VI shall promptly notify ASIVI and ASI of the achievement
     of any milestone.

4.2. Royalties.

               4.2.1.    Royalty on Net Sales by VI or its Affiliates. In
          partial consideration for the rights granted in Section 2.1, VI shall
          pay to ASIVI a royalty on annual Net Sales of Products sold by VI and
          its Affiliates, as follows:

<TABLE>
<CAPTION>
Annual VI Worldwide Net Sales                     Royalty Rate
-----------------------------                     ------------
<S>                                               <C>
[*]                                               [ * ]
[*]                                               [ * ]
</TABLE>

                                      -5-
<PAGE>   6
          [*]                                                    [*]
          [*]                                                    [*]

              4.2.2.  Royalty on Net Sales for Products Sold by Sublicensees. In
     partial consideration for the rights granted in Section 2.1, VI shall pay
     to ASIVI a royalty on annual Net Sales of Products sold by Sublicensees, as
     follows:

<TABLE>
<CAPTION>
        Annual Sublicensee Worldwide Net Sales            Royalty Rate
        --------------------------------------            ------------
        <S>                                               <C>
        [*]                                                    [*]
        [*]                                                    [*]
        [*]                                                    [*]
        [*]                                                    [*]
        [*]                                                    [*]
</TABLE>

              4.2.3.  Third Party Royalties. If VI, or any Affiliate or
     Sublicensee of VI becomes obligated to pay to third parties royalties or
     other amounts with respect to any Product through litigation or under
     agreements for patent rights or other technologies which VI, or such
     Affiliates or Sublicensee determines are desirable to license or acquire
     with respect to such Product, VI shall be responsible for making such
     payments. VI shall not deduct such payments from any payments to ASIVI, and
     such payments shall not be deducted from gross invoiced amounts for
     Products in calculating Net Sales.

              4.2.4.  One Royalty. No more than one royalty payment shall be due
     with respect to a sale of a particular Product.

              4.2.5.  Royalty Term. The royalties due under this Section 4.2
     shall be payable until the expiration of the last to expire Valid Claim.

5. PAYMENTS; REPORTS; AND RECORDS.

   5.1. Payments.

              5.1.1.  Timing of Payments. After the First Commercial Sale of a
     Product on which royalties are payable hereunder, VI shall make quarterly
     written reports to ASIVI within sixty (60) days after the end of each
     calendar quarter, stating in such report, separately for VI and each
     Affiliate and Sublicensee, the number, description and aggregate Net Sales,
     by country, of each Product sold during the calendar quarter upon which a
     royalty is payable. Such reports shall be Confidential Information of VI
     subject to the provisions of the Confidentiality and Non-Disclosure
     Agreement, dated December 16, 1999 by and between ASI, VI and ASIVI.
     Concurrently with the making of such reports, VI shall pay to ASIVI
     royalties due at the rates specified hereunder. Notwithstanding the
     foregoing, if VI receives provisional payments from Affiliates or
     Sublicensees relating to actual or anticipated sales of Products, VI must
     provide a quarterly written report containing the information specified
     above as it relates to such provisional payments, together with payment of
     royalties, at the rates specified in Section 4.2.2, on the amounts of such
     provisional payments (without setoff or deduction of any kind), within
     sixty (60) days after the end of each calendar quarter

                                      -6-
<PAGE>   7
          in which VI receives such provisional payments. Any necessary
          adjustments to be made to amounts paid as royalties on provisional
          payments (in order to effect payment of all royalties due on Net
          Sales) shall be made to the first payment due to ASI (for royalties
          not based on provisional payments) following the calendar quarter in
          which the applicable Products are sold.

               5.1.2. Payment Method. All payments due under this Agreement
          shall be made by bank wire transfer in immediately available funds to
          a bank account designated by ASIVI. All payments due to ASIVI
          hereunder shall be paid in United States dollars.

               5.1.3. Currency Conversion. If any currency conversion shall be
          required in connection with the calculation of amounts payable
          hereunder, such conversion shall be made using the buying exchange
          rate for conversion of the foreign currency into U.S. Dollars, quoted
          for current transactions reported in The Wall Street Journal (U.S.,
          Western Edition) for the last business day of the calendar quarter to
          which such payment pertains.

               5.1.4. Taxes. All payments required to be paid to ASIVI pursuant
          to this Agreement shall be paid with deduction for withholding for or
          on account of any applicable sales, use, value-added, or other
          federal, state or local taxes or import duties or tariffs, or similar
          governmental charges imposed by a jurisdiction other than the United
          States ("Withholding Taxes"). VI shall provide ASIVI a certificate
          evidencing payment of any Withholding Taxes hereunder, and shall
          provide any further assistance reasonably requested by ASIVI to enable
          ASIVI to obtain the benefit of any deduction.

          5.2. Reports: Inspection. VI shall maintain accurate books and records
     that enable the calculation of royalties payable hereunder to be verified.
     VI shall retain the books and records for each calendar year period for
     three (3) years after the submission of the corresponding report under
     Section 5.1.1 hereof. Upon thirty (30) days prior notice to VI, independent
     accountants selected by ASIVI, reasonably acceptable to VI, after entering
     into a confidentiality agreement with VI, may have access to VI's books and
     records during VI's normal business hours to conduct a review or audit once
     per calendar year, for the sole purpose of verifying the accuracy of VI's
     payments and compliance with this Agreement. Any such inspection or audit
     shall be at ASIVI's expense; however, if an inspection reveals underpayment
     of five percent (5%) or more in any audit period, VI shall pay the costs of
     the inspection. VI shall promptly pay to ASIVI any underpayment identified
     in such an audit.

6. CONFIDENTIALITY

          6.1. Confidential Information. The parties confidentiality and
     non-disclosure obligations relating to their respective Confidential
     Information are set forth in that certain Confidentiality and
     Non-Disclosure Agreement, dated December 16, 1999, by and between ASI, VI
     and ASIVI.

          6.2. Confidential Terms. Each party agrees not to disclose any terms
     of this Agreement to any third party without the consent of the other
     party; provided, disclosures may be made as required by securities or other
     applicable laws, or to a party's accountants, attorneys and other
     professional advisors, or by VI, ASIVI, and ASI to actual or prospective
     investors or corporate partners.

                                      -7-
<PAGE>   8
7. REPRESENTATIONS, WARRANTIES AND COVENANTS

         7.1.  ASIVI. ASIVI represents, warrants and covenants to VI that: (i)
      it is a limited liability company duly organized validly existing and in
      good standing under the laws of the State of Delaware; (ii) the execution,
      delivery and performance of this Agreement have been duly authorized by
      all necessary company action on the part of ASIVI; (iii) it is the sole,
      equal, and exclusive owner of all right, title and interest in the Patent
      Rights; (iv) it has the right to grant the rights and licenses granted
      herein, and the Patent Rights are free and clear of any lien, encumbrance
      or security interest; (v) it has not previously granted, and will not
      grant during the term of this Agreement, any right, license or interest in
      and to the Patent Rights, or any portion thereof, inconsistent with the
      license granted to VI herein; and (vi) there are no threatened or pending
      actions, lawsuits, claims or arbitration proceedings in any way relating
      to the Patent Rights.

         7.2.  VI. VI represents, warrants and covenants to ASIVI that: (i) it
      is a corporation duly organized validly existing and in good standing
      under the laws of the State of Delaware; (ii) the execution, delivery and
      performance of this Agreement have been duly authorized by all necessary
      corporate action on the part of VI; and (iii) it will use Commercially
      Reasonable Efforts to sell Products and to cause its Affiliates and
      Sublicensees to sell Products.

8. INTELLECTUAL PROPERTY

         8.1. Prosecution and Maintenance of Patent Rights. Following completion
      of the Priority IP Analysis provided in that certain Memorandum of
      Understanding dated October 14, 1999, ASIVI will form an Intellectual
      Property Advisory Committee ("IPAC") comprised of one representative each
      from ASI and VI. Each representative from ASI and VI may appoint up to two
      (2) additional IPAC members. It is understood that ASI and VI will each
      bear the costs, if any, of participating on this committee. The IPAC will
      meet at least on a quarterly basis and on an ad hoc basis as necessary to
      review and provide guidance with respect to the preparation, filing,
      prosecution and maintenance of any patent applications within the Patent
      Rights. VI will submit to the IPAC periodic reports at intervals no less
      frequently than quarterly, setting forth the status of all activities
      relating to the preparation, filing, prosecution and maintenance of any
      patent applications within the Patent Rights. VI shall have the right to
      control, at its own expense, the preparation, filing, prosecution and
      maintenance of any patent applications within the Patent Rights, subject
      to the following conditions with respect to each patent application within
      the Patent Rights: (1) VI, its attorneys and/or representatives involved
      in the prosecution of such application will promptly advise ASI of all due
      dates for any actions to be taken and will forward copies of all papers
      received from the U.S. Patent and Trademark Office ("USPTO") or foreign
      patent office within ten (10) days of receipt of such papers; (2) as soon
      as reasonably possible, but in no event more than thirty (30) days prior
      to the date for filing of any papers with the USPTO or foreign patent
      office, VI, its attorneys, and/or representatives involved in the
      prosecution of such application will forward to ASI drafts of such papers
      for review; (3) as soon as reasonably possible, but in no event more than
      fifteen (15) days of receipt of drafts of such papers, ASI, its attorneys
      and/or representatives will provide written comments and/or revised drafts
      of such papers to VI, its attorneys and/or representatives which VI, its
      attorneys and/or representatives agree to consider in good faith; (4) VI,
      its attorneys and/or representatives agree to prepare, file, prosecute,
      and maintain the Patent Rights in good faith with due consideration to all
      written comments and/or revised drafts of such papers provided by ASI, its
      attorneys and/or

                                      -8-
<PAGE>   9
representatives, and to use all commercially reasonable efforts to obtain and
maintain protection for the Product. In the event that VI, its attorneys and/or
representatives and ASI, its attorneys and/or representatives participating in
the IPAC cannot reach agreement regarding the filing of any paper with the USPTO
and/or foreign patent office, the issue(s) upon which there is disagreement will
be submitted to the Chief Executive Officer of VI and ASI to be resolved in good
faith.

     8.2. Enforcement. If either party hereto becomes aware that any Patent
Rights are being or have been infringed by any third party, such party shall
promptly notify the other party hereto in writing describing the facts relating
thereto in reasonable detail. VI shall have the initial right, but not the
obligation, to institute, prosecute and control any action, suit or proceeding
with respect to such infringement, including any declaratory judgment action
(each an "Action"), at its expense; using counsel of its choice. VI shall not be
entitled to offset any amount expended in connection with such Action against
royalties, if any, due under Section 3. In any such event, ASIVI shall cooperate
reasonably with VI in connection with any such Action, at VI's expense;
including without limitation, by joining such Action as a party if requested by
VI. In the event VI fails to initiate or defend any Action involving the Patent
Rights within three (3) months of receiving notice of any infringement, ASIVI
shall have the right, but not the obligation, to initiate and control such an
Action, at its expense; provided, any amounts recovered by ASIVI in such Action
shall be used first to reimburse ASIVI and VI for the expenses incurred in
connection with such Action and any remainder shall be treated as Net Sales of
Products pursuant to Section 4.

     8.3. Infringement Claims. If the practice by VI of the license granted
herein results in any allegation or claim of infringement of an intellectual
property right of a third party against VI, VI shall have the exclusive right to
defend any such claim, suit or proceeding, at its own expense, by counsel of its
own choice and shall have the sole right and authority to settle any such suit
without prejudice to ASIVI; provided, however, ASIVI shall cooperate reasonably
with VI, at VI's reasonable request and expense, in connection with the defense
of such claim. Notwithstanding the foregoing, ASIVI may participate in the
investigation and defense thereof, and any negotiations related thereto,
directly or through separate counsel chosen and paid for by ASIVI.

9. DISPUTE RESOLUTION

     If the parties are unable to resolve any dispute, controversy or claim
between them arising out of or relating to the validity, construction,
enforceability or performance of this Agreement, including disputes relating to
alleged breach or to termination of this Agreement (each, a "Dispute"), the
Dispute shall be settled by binding arbitration conducted in Chicago, Illinois,
or such other location mutually agreed to by the parties, pursuant to the
Commercial Arbitration Rules of the American Arbitration Association then in
effect by one (1) arbitrator appointed in accordance with such rules. The
decision and/or award rendered by the arbitrator shall be written (specifically
stating the arbitrator's findings of facts as well as the reasons upon which the
arbitrator's decision is based), final and nonappealable (except for an alleged
act of corruption or fraud on the part of the arbitrator) and may be entered in
any court of competent jurisdiction. The parties agree that, any provision of
applicable law notwithstanding, they will not request, and the arbitrator shall
have no authority to award punitive or exemplary damages against any party. The
arbitrator shall determine what discovery will be permitted, consistent with the
goal of limiting the cost and time that the parties must expend for discovery;
provided the arbitrator shall permit such discovery as he or she deems necessary
to permit an equitable resolution of the dispute. Evidence need not be obtained
in the presence of the arbitrator. At the arbitration hearing, each party may
make written and oral presentations

                                      -9-
<PAGE>   10
to the arbitrator, present testimony and written evidence, and examine
witnesses. The costs of any arbitration, including administrative fees and fees
of the arbitrator, shall be shared equally by the parties. Each party shall bear
the cost of its own attorneys' fees and expert fees. The parties and the
arbitrator shall use their best efforts to complete any such arbitration within
one (1) year after the appointment of the arbitrator, unless a party can
demonstrate to the arbitrator that the complexity of the issues or other reasons
warrant the extension of the timetable. In such case, the arbitrator may extend
such timetable as reasonably required. The arbitrator shall, in rendering his or
her decision, apply the substantive law of the State of Delaware, without regard
to its conflict of laws provisions, except that the interpretation of and
enforcement of this Article 9 shall be governed by the U.S. Federal Arbitration
Act. Notwithstanding the foregoing, either party may seek from any court of
competent jurisdiction any interim or provisional relief including injunctive
and other equitable relief as appropriate. If a party seeks injunctive or other
equitable relief in the event of a breach or threatened breach of this Agreement
by the other party, such other party agrees that it shall not allege in any such
proceeding that the party seeking such relief has an adequate remedy at law. If
a party seeks any equitable remedies (including injunctive relief), it shall not
be precluded or prevented from seeking remedies at law, nor shall it be deemed
to have made an election of remedies.

10. INDEMNIFICATION

          10.1. Indemnification of ASIVI. VI shall indemnify, defend and hold
       harmless ASIVI and its directors, officers and employees (each an "ASIVI
       Indemnitee") from and against any and all liabilities, damages, losses,
       costs or expenses (including reasonable attorneys' and professional fees
       and other expenses of litigation and/or arbitration) (a "Liability")
       resulting from a claim, suit or proceeding (any of the foregoing, a
       "Claim") brought by a third party against an ASIVI Indemnitee, arising
       from or occurring as a result of activities performed by VI, its
       Affiliates, or its Sublicensees in connection with the development,
       manufacture or sale of any Product, except to the extent caused by the
       negligence or willful misconduct of ASIVI.

          10.2. Indemnification of VI. ASIVI shall indemnify, defend and hold
       harmless VI, its Affiliates, Sublicensees and their directors, officers
       and employees (each a "VI Indemnitee") from and against any and all
       liabilities, damages, losses, costs or expenses (including reasonable
       attorneys' and professional fees and other expenses of litigation and/or
       arbitration) (a "Liability") resulting from a claim, suit or proceeding
       (any of the foregoing, a "Claim") brought by a third party against a VI
       Indemnitee, arising from or occurring as a result of (a) a material
       breach by ASIVI of its obligations under this Agreement, or (b) the
       negligence or willful misconduct of ASIVI, except, in each case, to the
       extent caused by the negligence or willful misconduct of VI, its
       Affiliates or Sublicensees.

          10.3. Indemnification Procedures. In the event that an Indemnitee
       intends to claim indemnification under this Article 10, it shall promptly
       notify the other party (the "Indemnitor") in writing of such alleged
       Liability. The Indemnitor shall have the sole right to control the
       defense and/or settlement thereof, provided that the indemnified party
       may participate in any such proceeding with counsel of its choice at its
       own expense. The indemnity agreement in this Article 10 shall not apply
       to amounts paid in settlement of any Claim if such settlement is effected
       without the consent of the Indemnitor, which consent shall not be
       withheld unreasonably. The failure to deliver written notice to the
       Indemnitor within a reasonable time after the commencement of any such
       action, if prejudicial to its ability to defend such action, shall
       relieve such Indemnitor of any liability to the Indemnitee under this
       Article 10 but the omission so to deliver written notice

                                      -10-
<PAGE>   11
     to the Indemnitor shall not relieve the Indemnitor of any liability that it
     may have to any Indemnitee other than under this Article 10. The Indemnitee
     under this Article 10, its employees and agents, shall cooperate fully with
     the Indemnitor and its legal representatives and provide full information
     in the investigation of any Claim covered by this indemnification. Neither
     party shall be liable for any costs or expenses incurred by the other party
     without its prior written authorization.

11. TERM AND TERMINATION

          11.1. Term. The term of this Agreement shall commence on the Effective
     Date, and unless earlier terminated as provided in this Article 11, shall
     continue in full force and effect until the expiration of the last to
     expire Valid Claim.

          11.2. Termination for Cause. Either party will have the right to
     terminate this Agreement upon sixty (60) days notice of a material breach
     by the other party, provided that the party accused of breach may avoid
     such termination if before the end of such sixty (60) day period said party
     cures such breach or default. However, if the party accused of breach
     disputes an asserted breach in writing within such sixty (60) day period,
     the non-breaching party shall not have the right to terminate this
     Agreement unless and until it has been determined in an arbitration
     proceeding under Article 9 above that this Agreement was materially
     breached, and the party accused of breach fails to cure such breach within
     sixty (60) days after such determination.

          11.3. Termination for Insolvency. Either party may terminate this
     Agreement if the other becomes the subject of a voluntary or involuntary
     petition in bankruptcy or any proceeding relating to insolvency,
     receivership, liquidation, or composition for the benefit of creditors, if
     that petition or proceeding is not dismissed with prejudice within sixty
     (60) days after filing.

          11.4. Effect of Termination.

                11.4.1.  Accrued Rights and Obligations. Termination of this
          Agreement for any reason shall not release any party hereto from any
          liability which, at the time of such termination, has already accrued
          to the other party or which is attributable to a period prior to such
          termination, nor preclude either party from pursuing any rights and
          remedies it may have hereunder or at law or in equity which accrued or
          are based upon any event occurring prior to such termination.

                11.4.2.  Return of Confidential Information. The parties'
          obligations with respect to the return of Confidential Information is
          as set forth in that certain Confidentiality and Non-Disclosure
          Agreement, dated December 16, 1999, by and between ASI, VI and ASIVI.

                11.4.3.  Stock on Hand. In the event this Agreement is
          terminated for any reason, VI and its Affiliates and Sublicensee(s)
          shall have the right to sell or otherwise dispose of the stock of any
          Product then on hand, subject to Articles 4 and 5.

                11.4.4.  Sublicense. In the event of any termination of this
          Agreement, any sublicense by VI shall remain in force and effect.

                                      -11-
<PAGE>   12
     11.5.  Survival. Sections 8.1, 11.4 and 11.5 and Articles 4, 5, 6, 9 and 12
of this Agreement shall survive termination of this Agreement for any reason.

12. MISCELLANEOUS

     12.1.  Governing Law. This Agreement, and any proceeding subject to Article
9, shall be governed by and construed in accordance with the laws of the State
of Delaware, without reference to its conflicts of laws provisions.

     12.2.  Independent Contractors. The relationship of the parties hereto is
that of independent contractors. The parties hereto are not deemed to be
agents, partners or joint ventures of the other for any purpose as a result of
this Agreement or the transactions contemplated thereby. Neither party shall
have the power to obligate or bind the other party in any manner whatsoever.

     12.3.  Assignment. The parties agree that their rights and obligations
under this Agreement shall not be delegated, transferred or assigned to a third
party without the prior written consent of the other party hereto; provided that
either party may assign all of its rights and obligations under this Agreement,
without the other party's consent (a) to its Affiliates, and (b) to an entity
that acquires all or substantially all of the business or assets of the
assigning party to which this Agreement pertains, whether by merger,
reorganization, acquisition, sale or otherwise; which Affiliate or acquiring
entity (y) agrees in a writing provided to the non-assigning party prior to any
assignment, to assume all of the obligations of the assigning party hereunder,
and (z) has provided to the non-assigning party evidence reasonably satisfactory
to the non-assigning party of its ability to perform all such obligations in a
timely manner. This Agreement shall be binding upon and inure to the benefit of
the parties and their successors and permitted assigns.

     12.4.  Notices. Any notice required or permitted by this Agreement shall be
in writing and shall be sent by hand delivery, by prepaid registered or
certified mail, return receipt requested, or by facsimile transmission,
addressed to the other party at the address shown below or at such other address
for which such party gives notice hereunder. Such notice shall be deemed to have
been given upon delivery, if sent by hand delivery, three (3) days after deposit
in the mail, or upon transmission by facsimile.

To ASIVI:           ASIVI, LLC
                    1172 Castro Street
                    Mountain View, California 94040
                    Attention: Leland F. Wilson, President, CEO
                    Facsimile: (650) 934-5356

With a copy to:     AndroSolutions, Inc.
                    200 Fort Sanders West Blvd., Suite 309
                    Knoxville, TN 37922
                    Attention: Gary W. Neal, M.D., President
                    Facsimile: (423) 531-6550

                                      -12-
<PAGE>   13
And with a copy to:      Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
                         One Fountain Square
                         11911 Freedom Drive
                         Reston, VA 20190
                         Attention: Martin M. Zoltick, Esq.
                         Facsimile: (703) 464-4895

To VIVUS:                VIVUS, Inc.
                         1172  Castro Street
                         Mountain View, CA 94040
                         Attention: Leland F. Wilson, President, CEO
                         Facsimile: (650) 934-5356

With a copy to:          Wilson Sonsini Goodrich & Rosati, PC
                         650 Page Mill Road
                         Palo Alto, CA 94304
                         Attention: Mark Casper, Esq.
                         Facsimile: (650) 496-4082

     12.5.  Force Majeure.  Neither party shall lose any rights hereunder or be
liable to the other party for damages or losses (except for payment
obligations) on account of failure of performance if such failure is occasioned
by war, strike, fire, Act of God, earthquake, flood, lockout, embargo,
governmental acts or orders or restrictions, failure of suppliers, or any other
reason where failure to perform is beyond the reasonable control and not caused
by the negligence, intentional conduct or misconduct of the nonperforming party
and such party has exerted all reasonable efforts to avoid or remedy such force
majeure; provided, however, that in no event shall a party be required to
settle any labor dispute or disturbance.

     12.6.  Advice of Counsel.  VI and ASIVI have each consulted counsel of
their choice regarding this Agreement, and each acknowledges and agrees that
this Agreement shall not be deemed to have been drafted by one party or another
and will be construed accordingly.

     12.7.  Compliance with Laws.  Each party shall furnish to the other party
any information requested or required by that party during the term of this
Agreement or any extensions hereof to enable that party to comply with the
requirements of any U.S. or foreign, state and/or government agency.

     12.8.  LIMITATION OF LIABILITY.  NEITHER PARTY SHALL BE LIABLE TO THE
OTHER FOR ANY SPECIAL, CONSEQUENTIAL, INCIDENTAL OR INDIRECT DAMAGES ARISING
OUT OF THIS AGREEMENT, HOWEVER CAUSED, UNDER ANY THEORY OF LIABILITY, OR FOR
ANY LOST PROFITS, BUSINESS OR REVENUE, LOSS OF USE OR GOODWILL, OR OTHER LOST
ECONOMIC ADVANTAGE, ARISING OUT OF OR RELATED TO THIS AGREEMENT OR THE BREACH
HEREOF, WHETHER SUCH CLAIMS ARE BASED ON BREACH OF CONTRACT, STRICT LIABILITY,
TORT, ANY FEDERAL OR STATE STATUTORY CLAIM, OR ANY OTHER LEGAL THEORY AND EVEN
IF THE OTHER PARTY KNEW, SHOULD HAVE KNOWN, OR HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. THE LIMITATION SPECIFIED IN THIS SECTION 12.9
SHALL SURVIVE AND APPLY EVEN IF ANY LIMITED

                                      -13-
<PAGE>   14
     REMEDY SPECIFIED IN THIS AGREEMENT IS DETERMINED TO HAVE FAILED OF ITS
     ESSENTIAL PURPOSE.

          12.9.  Further Assurances.  At any time from time to time on and after
     the date of this Agreement, ASIVI shall at the request of VI: (i) deliver
     to VI such records, data or other documents consistent with the provisions
     of this Agreement, (ii) execute, and deliver or cause to be delivered, all
     such consents, documents or further instruments, and (iii) take or cause to
     be taken all such actions; as VI may reasonably deem necessary or desirable
     in order for VI to obtain the full benefits of this Agreement and the
     transactions contemplated hereby.

          12.10.  Severability; Waiver.  If any provision(s) of this Agreement
     are determined to be invalid or unenforceable by a court of competent
     jurisdiction, the remainder of the Agreement shall remain in full force and
     effect without said provision. The parties shall in good faith negotiate a
     substitute clause for any provision declared invalid or unenforceable,
     which shall most nearly approximate the intent of the parties in entering
     this Agreement. The failure of a party to enforce any provision of the
     Agreement shall not be construed to be a waiver of the right of such party
     to thereafter enforce that provision or any other provision or right.

          12.11.  Entire Agreement; Modification.  This Agreement sets forth the
     entire agreement and understanding of the parties with respect to the
     subject matter hereof, and supersedes all prior discussions, agreements and
     writings in relating thereto. This Agreement may not be altered, amended or
     modified in any way except by a writing signed by both parties.

          12.12.  Counterparts.  This Agreement may be executed in two
     counterparts, each of which shall be deemed an original and which together
     shall constitute one instrument.

     IN WITNESS WHEREOF, ASIVI and VI have caused this Agreement to be executed
by their respective duly authorized representatives as of the date first
written above.

     ASIVI, LLC                           VIVUS, INC.

     By: /s/ Gary W. Neal                 By: /s/ Leland F. Wilson
         -----------------------------        -----------------------------
         AndroSolutions, Inc.                 Leland F. Wilson
         Managing Member                      President/Chief Executive Officer
         Gary W. Neal, M.D., President

     By:  /s/ Leland F. Wilson
         -----------------------------
         VIVUS, Inc.
         Managing Member
         Leland F. Wilson
         President/Chief Executive Officer

                                      -14-

<PAGE>   15
                                                                    EXHIBIT 1.13

                       [ANDRO SOLUTIONS, INC. LETTERHEAD]

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                                       2
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                                       3
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                                       4
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                                       5
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                                       6
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                                       9
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                                       10
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                                                                    EXHIBIT 1.18

                               (VIVUS letterhead)

                                      [*]

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