Document:

<PAGE>   1
                                                                   EXHIBIT 10.13

                        CONFIDENTIAL TREATMENT REQUESTED

         Confidential Portions Of This Agreement Which Have Been Redacted Are
Marked With Brackets ([***]). The Omitted Material Has Been Filed Separately
With The Securities And Exchange Commission.

                            PRODUCT SUPPLY AGREEMENT

         THIS PRODUCT SUPPLY AGREEMENT (the "Agreement") is entered into as of
January 29, 1999 (the "Effective Date"), by and between AMERICAN HOME PRODUCTS
CORPORATION, located at Five Giralda Farms, Madison, New Jersey 07940
(hereinafter "AHP"), and HORIZON PHARMACEUTICAL CORPORATION located at 660
Hembree Parkway, Suite 106, Roswell, Georgia 30076 (hereinafter "Horizon"). AHP
and Horizon may each be referred to herein individually as a "Party" and
collectively as the "Parties."

         WHEREAS, on January 29, 1999 Horizon and AHP entered into a license
agreement concerning AHP's grant of a license to Horizon of AHP's interest in
the Robinul(R) oral dosage form human pharmaceutical business in the United
States, its territories and possessions (including the Commonwealth of Puerto
Rico); and

         WHEREAS, Horizon desires AHP to manufacture or have manufactured and
supply to Horizon certain Robinul(R) products for sale by Horizon in the
Territory (as such term is defined below) and AHP desires to manufacture or
have manufactured and supply Horizon with such products on the terms and
conditions set forth herein.

         NOW THEREFORE, in consideration of the foregoing premises and the
mutual premises, covenants and conditions contained in this Agreement, the
Parties agree as follows:

1.       DEFINITIONS.

         As used in this Agreement, the following terms shall have the
         following respective meanings:

         1.1      "ACCEPTABLE PRODUCT" shall have the meaning set forth in
                  Section 6.1 hereof.

         1.2      "AFFILIATE" shall mean, in the case of either Party, any
                  corporation, joint venture, or other business entity which
                  directly or indirectly controls, is controlled by, or is
                  under common control with that Party. "Control", as used in
                  this Section 1.2, shall mean having the power to direct, or
                  cause the direction of, the management and policies of an
                  entity, whether through ownership of voting securities, by
                  contract or otherwise. Notwithstanding the foregoing, for
                  purposes of this Agreement, the term "Affiliate" shall not
                  include subsidiaries in which a Party or its Affiliates owns
                  a majority of the ordinary voting power to elect a majority
                  of the board of directors but is restricted from electing
                  such majority by contract or otherwise, until such time as
                  such restrictions are no longer in effect.

<PAGE>   2

         1.3      "BINDING QUARTERLY FORECAST" shall have the meaning set forth
                  in Section 2.3.1.

         1.4      "CALENDAR QUARTER" shall mean the respective periods of three
                  (3) consecutive calendar months ending on March 31, June 30,
                  September 30 or December 31, for so long as this Agreement is
                  in effect.

         1.5      "CERTIFICATE OF ANALYSIS" shall mean the certificate for each
                  batch of Product delivered hereunder in the form contemplated
                  by Section 2.6 of this Agreement.

         1.6      "CGMP" shall mean current good manufacturing practices of the
                  FDA, including compliance with the FD&C Act, 21 C.F.R. parts
                  210 and 211 and all applicable FDA rules, regulations,
                  policies and guidelines in effect at a given time.

         1.7      "COMMERCIALLY REASONABLE EFFORTS" shall mean efforts and
                  resources normally used by a Party for a compound or product
                  owned by it or to which it has rights, which is of similar
                  market potential at a similar stage in its product life,
                  taking into account the competitiveness of the marketplace,
                  the proprietary position of the compound or product, the
                  regulatory structure involved, the profitability of the
                  applicable products, and other relevant factors.

         1.8      "FDA" shall mean the United States Food and Drug
                  Administration, and any successor thereto.

         1.9      "FD&C ACT" shall mean the United States Federal Food, Drug and
                  Cosmetic Act, as amended.

         1.10     "FULLY ABSORBED COST" shall mean with respect to AHP's
                  manufacture of the Product, the sum of AHP's standard unit
                  costs of raw materials, direct labor and allocated overhead.
                  The calculation of direct labor and allocated overhead costs
                  will be consistent with AHP's then current cost accounting
                  policies and procedures and in accordance with generally
                  accepted accounting procedures.

         1.11     "KNOW-HOW" shall mean all proprietary technical and clinical
                  information, data and know-how relating to the manufacture of
                  the Product, whether or not patentable, owned or controlled,
                  as of the Effective Date or acquired during the term of this
                  Agreement, by AHP or its Affiliates (with the right to have
                  or disclose). Know-How shall include, without limitation, all
                  processes, formulas, discoveries and inventions whether
                  relating to biological, chemical, pharmacological,
                  toxicological, pharmaceutical, physical and analytical
                  safety, quality control and clinical data, including, without
                  limitation, phase IV clinical study data. The term
                  "Know-How", however, shall not include (i) any know-how,
                  processes, information and data which is, as of the Effective
                  Date or later becomes, generally available to the public or
                  (ii) any general manufacturing know-how not specific to the
                  Product.

         1.12     "LICENSE AGREEMENT" shall mean the License Agreement between
                  AHP and Horizon relating to, among other things, the grant by
                  AHP to Horizon of an exclusive license pertaining to certain
                  of AHP's Robinul(R) Products within the Territory which
                  License Agreement was executed on January 29, 1999.

<PAGE>   3

         1.13     "MATERIALS" shall mean any or all Substances, inactive
                  ingredients, excipients, components, labels, packaging
                  materials and other consumable materials used in the
                  manufacture of the Products, provided, however, that
                  Materials shall not include any equipment used in the
                  manufacture of the Products.

         1.14     "MG." shall mean milligrams.

         1.15     "NDA" shall mean a New Drug Application as defined in the
                  FD&C Act and applicable regulations thereunder, as amended
                  from time to time.

         1.16     "PRODUCTS" shall mean the following compositions and dosage
                  forms containing Substance in the following amounts and
                  supplied to Horizon pursuant to this Agreement:

<TABLE>
                           <S>                        <C>
                           Product A                  (Robinul(R))
                           Tablets
                           Glycopyrrolate
                           1 mg.
                           Supplied in:               Bottles of 100

                           Product B                  (Robinul(R) Forte)
                           Tablets
                           Glycopyrrolate
                           2 mg.
                           Supplied in:               Bottles of 100
</TABLE>

                           In addition, Products shall include 1 mg. Tablets
                           (Product C) and 2 mg. Tablets (Product D) supplied
                           in bulk but only for Horizon's requirements to
                           self-package for sampling purposes.

                           It is understood by the Parties hereto that the
                           Products are to (a) be substantially similar to
                           those Products currently manufactured and marketed
                           by AHP in the Territory, (b) comply with the
                           Specifications and (c) be sold under the trademark
                           Robinul(R).

         1.17     "REGULATORY APPROVALS" shall mean all (i) authorizations by
                  the appropriate Regulatory Authorities which are required for
                  the manufacture (other than manufacturing facility licenses,
                  approvals or authorizations), marketing, promotion, pricing
                  and sale of the Products in the Territory, and (ii)
                  investigational new drug applications permitting the clinical
                  study of the Product in the Territory, each of which are
                  owned by AHP or its Affiliates.

         1.18     "REGULATORY AUTHORITY" shall mean any national,
                  supra-national, regional, state or local regulatory agency,
                  department, bureau, commission, council or other governmental
                  entity in the Territory involved in the granting of
                  Regulatory Approval for the Product, including, without
                  limitation, the FDA.

         1.19     "SPECIFICATIONS" shall mean specifications for or concerning
                  the manufacturing, testing, and packaging of Products as set
                  forth in the Regulatory Approvals for the Product and in
                  Schedule 1.19 hereto, or as may be agreed upon by the Parties
                  in writing from time to time.

<PAGE>   4

         1.20     "SUBSTANCE" shall mean the chemical substance
                  3-[(cyclopentylhydroxy phenylacetyl)oxy]-1,
                  1-dimethylpyrrolidinium bromide, otherwise known as
                  glycopyrrolate.

         1.21     "TERM" shall have the meaning set forth in Section 10.1
                  hereof.

         1.22     "TERRITORY" shall mean the United States, its territories and
                  possessions (including the Commonwealth of Puerto Rico).

         1.23     "THIRD PARTY(IES) shall mean any person(s) or party(ies)
                  other than Horizon, AHP or their respective Affiliates.

         1.24     "TRANSACTION AGREEMENTS" shall mean this Agreement and the
                  License Agreement.

         1.25     "$" shall mean United States dollars.

2.       SUPPLY OF PRODUCTS.

         2.1      OBLIGATION TO SUPPLY. Subject to the provisions of this
                  Agreement, during the Term of this Agreement, AHP shall
                  manufacture or have manufactured for and supply to Horizon
                  Products for sale by Horizon, its Affiliates or its permitted
                  sublicensees in the Territory, and Horizon shall purchase
                  from AHP its entire requirements of Products for sale in the
                  Territory. All Products supplied under this Agreement are to
                  be supplied in finished form, as specified in Horizon's
                  purchase orders placed with AHP pursuant to Section 2.4
                  below.

         2.2      SUBCONTRACTING; ASSIGNMENT OF OBLIGATIONS.

                  2.2.1    RIGHT TO SUBCONTRACT OR ASSIGN.  AHP may subcontract
                           or assign any part of its manufacturing and supply
                           obligations hereunder if it provides no less than
                           six (6) months' written notice of its intent to do
                           so to Horizon, subject to Horizon's prior right to
                           take over such manufacturing and supply obligations.
                           AHP and Horizon agree that, prior to transfer of
                           manufacturing obligations to such subcontractor or
                           assignee, such subcontractor or assignee must (i)
                           have an FDA approved facility for the manufacture of
                           Product and a supplement to the Regulatory Approvals
                           permitting the manufacture of Product in such
                           facilities must be approved by the FDA, and (ii)
                           must agree in writing to comply with the obligations
                           set forth in this Agreement. AHP shall assist in the
                           qualification of such third party manufacturers or
                           Horizon; provided, however, that AHP's assistance
                           shall be limited to providing reasonable technical
                           assistance not to exceed 30 man-days and the
                           delivery of the following documentation: Batch
                           records for both strengths of the Product, copies of
                           change control history, all method validations
                           (including new HPLC methods), active ingredient
                           specification sheets, raw material test procedures,
                           copies of process and cleaning validations, and a
                           copy of the Product dossier made available to
                           Horizon during the due diligence process. AHP shall
                           notify Horizon or obtain Horizon's consent with
                           respect to its purchase of Materials from qualified
                           Third Parties for use in its manufacture of Product
                           hereunder.

<PAGE>   5

                  2.2.2    COSTS. In the event that (i) during the Term of this
                           Agreement AHP subcontracts or assigns its
                           manufacturing and supply obligations to a Third
                           Party pursuant to Horizon's request or (ii) Horizon
                           assumes, either directly or through a Third Party,
                           the responsibilities for manufacturing and supplying
                           Product during the Term of this Agreement as
                           permitted under Section 2.2.1 hereof, Horizon shall
                           pay the out-of-pocket expenses incurred by either
                           Party in transferring such manufacturing and supply
                           responsibilities.

         2.3      FORECASTS

                  2.3.1    ROLLING FORECASTS. Throughout the term of this
                           Agreement, Horizon shall provide AHP with a rolling
                           one (1) year forecast of its expected purchases of
                           each Product, the mechanism for which shall be as
                           follows:

                  (i)      On or before the Effective Date, Horizon shall have
                           provided AHP with a written forecast of its expected
                           purchases of each of the Products for the period
                           extending three (3) Calendar Quarters beyond the
                           Calendar Quarter containing the Effective Date.
                           Subject to Section 2.3.2, the forecast for this
                           period, excluding the last two (2) Calendar
                           Quarters, shall be binding upon Horizon.

<PAGE>   6

                  (ii)     Beginning on the date of the first Calendar Quarter
                           following the Effective Date and then on or prior to
                           the first day of each subsequent Calendar Quarter,
                           Horizon shall provide AHP with an update to its
                           previously submitted forecast of its expected
                           purchases of each of the Products. Such update shall
                           consist of a repetition of the previously forecasted
                           three (3) Calendar Quarters along with a newly
                           introduced forecast for the Calendar Quarter
                           subsequent to the last Calendar Quarter previously
                           forecasted, provided, however, that the quantity
                           forecasted for each Product for any Calendar Quarter
                           shall not, without AHP's prior written consent, be
                           more than one hundred twenty-five percent (125%) of
                           the quantity forecasted for such Product for the
                           immediately preceding Calendar Quarter. Subject to
                           Section 2.3.2, the forecast for this period,
                           excluding the last two (2) Calendar Quarters, shall
                           be binding upon Horizon.

                  (iii)    Under each of Sections 2.3.1(i) and 2.3.1(ii) above,
                           the forecast for those quarters which is binding
                           upon Horizon shall be a "Binding Quarterly
                           Forecast."

                  2.3.2    QUANTITY LIMITATIONS.  The quantity of each Product
                           ordered by Horizon to be supplied by AHP in
                           accordance with such orders in any Calendar Quarter
                           shall not be less than seventy-five percent (75%) of
                           the quantity of such Product specified in the most
                           recent Binding Quarterly Forecast applicable to such
                           Calendar Quarter. Additionally, AHP shall not be
                           obligated to supply that quantity of any Product in
                           any Calendar Quarter that is more than one hundred
                           twenty-five percent (125%) of the quantity of such
                           Product specified for the most recent Binding
                           Quarterly Forecast applicable to such Calendar
                           Quarter, but shall use its Commercially Reasonable
                           Efforts to meet requirements in excess of such
                           quantity. AHP shall provide sixty (60) days' written
                           notice to Horizon in the event AHP determines that
                           it cannot fill an order.

         2.4      PURCHASE ORDERS

                  2.4.1    SUBMISSION OF PURCHASE ORDERS. From time to time,
                           Horizon shall place purchase orders with AHP, in a
                           format agreed upon by the Parties, for each of the
                           Products specifying the quantities of the Products
                           desired, and the place(s) to which and the manner
                           and dates by which delivery is to be made; said
                           delivery dates to be no earlier than one hundred
                           twenty (120) calendar days after the purchase order
                           date. All purchase orders shall be sent by Horizon
                           to the attention of the following employee of AHP or
                           as otherwise instructed by AHP.

                           Wyeth-Ayerst Pharmaceuticals
                                    P.O. Box 861
                                    Paoli, PA  19301
                                    Attn:   Mr. Tom Higgins,
                                            Finished Stock Requirements Division
                                    FAX:  (610) 651-3659

<PAGE>   7
                                          [***]-CONFIDENTIAL TREATMENT REQUESTED

                           Purchase orders made in accordance with the
                           provisions of this Article 2 shall be deemed to be
                           accepted by AHP if AHP has not rejected said
                           purchase orders within ten (10) business days of
                           receipt of the same, provided, however, that AHP
                           shall not reject any purchase order specifying
                           quantities within the quantity limitations set forth
                           in Section 2.3.2 hereof and which purchase orders
                           are otherwise in accordance with the provisions of
                           this Article 2. To the extent the terms of any
                           purchase order or acknowledgment thereof are
                           inconsistent with the terms of this Agreement, the
                           terms of this Agreement shall control.

                  2.4.2    SIZE OF ORDERS. All purchase orders for each Product
                           placed by Horizon shall be whole number multiples of
                           the production batch sizes used by AHP. These are
                           set forth below (or as mutually agreed in writing by
                           the Parties):

<TABLE>
<CAPTION>
                                    Product                   Batch Size - Expected Yield

                                    <S>                       <C>
                                    Products A and C
                                    1 mg. tablets                      [***] tablets

                                    Products B and D
                                    2 mg. tablets                      [***] tablets
</TABLE>

         2.5      DELIVERY. AHP shall execute all accepted purchase orders
                  consistent with this Agreement by delivery ex works to
                  Horizon's designated carrier at AHP's manufacturing or
                  distribution facility of all ordered quantities of the
                  Products no later than the delivery dates provided in
                  Horizon's purchase orders. Title and risk of loss will pass
                  to Horizon when each order of Products is delivered to the
                  designated carrier of Horizon at AHP's manufacturing or
                  distribution facility.

         2.6      SPECIFICATIONS; CERTIFICATE OF ANALYSIS. As of the time of
                  such delivery by AHP, each batch of the Products will conform
                  to the Specifications. AHP shall perform release testing in a
                  manner consistent with testing methods agreed upon by the
                  Parties. AHP shall provide to Horizon a Certificate of
                  Analysis with each shipment of the Products to Horizon or its
                  designated recipient stating that the Products conform to the
                  Specifications and meet release specifications. The
                  Certificate of Analysis shall be in a format agreed upon by
                  the Parties and, if required under cGMP, such Certificate of
                  Analysis shall include the Specifications and the results of
                  release testing conducted by AHP on such Products. Upon
                  Horizon's written request, AHP will also provide Horizon with
                  a copy of the manufacturing and controls information for the
                  applicable batch(es) delivered.

         2.7      LABELING. Within thirty (30) days after the Effective Date,
                  Horizon, at its own expense, will provide AHP with Horizon's
                  new labeling for the Product (including a new NDC number for
                  each Product) bearing Horizon's corporate name and trade
                  dress. If such labeling is changed in any manner other than a
                  new NDC number and Horizon's corporate name and tradedress,
                  such labeling shall be subject to the approval of AHP, which
                  approval will not be unreasonably withheld. AHP agrees to
                  either approve or disapprove such labeling within thirty (30)
                  business days of AHP's receipt thereof from Horizon. AHP, at
                  Horizon's expense, will print, either directly or through a
                  Third Party, labels and other printed material to be included
                  as part of the finished Product.  Product

<PAGE>   8

                  manufactured by AHP after AHP's receipt and approval of
                  Horizon's new labeling for the Product, shall bear such new
                  labeling, provided, however, that AHP shall have no
                  responsibility with respect to the content of such labeling,
                  provided the content of the labeling printed by AHP is the
                  same as the content of the labeling provided by Horizon.
                  Horizon shall reimburse AHP for all reasonable costs incurred
                  (on a Fully-Absorbed Cost basis) by AHP in making
                  modifications to labeling, branding or imprinting, packaging
                  and/or manufacturing processes to accommodate Horizon's new
                  labeling or to accommodate any other changes requested by
                  Horizon. Such reimbursement shall be made pursuant to invoices
                  submitted by AHP to Horizon, which invoices shall be payable
                  within thirty (30) days after Horizon's receipt thereof. In
                  addition, should such new labeling result in any increase in
                  AHP's cost of manufacturing the Product hereunder, the
                  purchase price for such Product as calculated under Section
                  5.1 hereof, shall be increased by such additional costs.
                  Notwithstanding the foregoing, AHP may supply Horizon with
                  Product bearing AHP's labeling if such Product was
                  manufactured and labeled prior to the Closing, it being agreed
                  that Product manufactured from and after the Closing shall
                  bear (i) AHP's label, or (ii) Horizon's new label.

         2.8      PURCHASE OF RESIDUAL INVENTORIES. Upon expiration or upon
                  termination of this Agreement by AHP, upon AHP's request
                  Horizon shall purchase from AHP (i) reasonable quantities of
                  AHP's residual inventories of Products having not less than
                  twelve months' remaining dating at the then current purchase
                  price as determined in accordance with Section 5.1 hereof,
                  and (ii) reasonable quantities of AHP's residual inventories
                  of Product specific Materials, including, without limitation,
                  all labels and other Product specific packaging materials,
                  but excluding all stocks of Substance and Materials used for
                  the manufacture of Substance, at AHP's Fully Absorbed Cost
                  for such Materials.

         2.9      INITIAL DELIVERY. AHP agrees to provide initial delivery of
                  Products, subject to the timely receipt of an appropriate
                  purchase order from Horizon in accordance with this Article
                  2, on or before Closing in accordance with procedures and
                  terms to be set forth in the Systems Transfer documents
                  developed by the Parties pursuant to Section 3.2 of the
                  License Agreement.

3.       MANUFACTURE OF PRODUCTS.

         3.1      MANUFACTURE OF PRODUCT. AHP agrees to manufacture and supply
                  the Products in accordance with (i) the Specifications, (ii)
                  the applicable Regulatory Approvals, as may be amended from
                  time to time, and (iii) cGMP requirements, and all other
                  applicable laws, rules and regulations. If

                           (a)      upon Horizon's request the Parties mutually
                                    agree to change part or all of the Product
                                    manufacturing process, or

                           (b)      any Product specific change in the
                                    applicable Regulatory Approvals (other than
                                    a change included under clause (a) above),
                                    applicable laws, rules or regulations
                                    requires a change in the Product
                                    manufacturing process

<PAGE>   9

                  Horizon shall reimburse AHP for all Fully Absorbed Costs
                  incurred by AHP in connection with making such changes in the
                  Product manufacturing process. Additionally, if either making
                  any such change in the Product manufacturing process or any
                  Product specific change in the applicable Regulatory
                  Approvals, applicable laws, rules or regulations requires AHP
                  to conduct development, testing or other activities (e.g.,
                  process development, stability testing, validation of new
                  specifications, etc...) (collectively referred to as
                  "Activities") in addition to those activities AHP conducted
                  or is required to conduct in its manufacture of the Product
                  immediately prior to such change in either the Product
                  manufacturing process or the Product specific applicable
                  Regulatory Approvals, applicable laws, rules or regulations
                  being implemented, Horizon shall reimburse AHP for all Fully
                  Absorbed Costs incurred by AHP in connection therewith. In
                  addition to the foregoing, in the event that the Product
                  manufacturing process is changed or AHP is required to
                  conduct Activities in accordance with this Section 3.1, the
                  purchase price for Product, other than for Product already
                  manufactured and in inventory, shall be increased in an
                  amount equivalent to the increase in AHP's manufacturing cost
                  for Product, which increase shall be effective immediately
                  upon AHP becoming aware of any proposed changes in the
                  Regulatory Approvals, applicable laws, rules or regulations
                  which requires either (i) a change in the Product
                  manufacturing process or (ii) to AHP to conduct Activities,
                  it will promptly notify Horizon and will consult with Horizon
                  regarding the proposed changes and Activities, and will
                  obtain Horizon's written consent prior to implementing the
                  Activities and the changes, which consent shall not be
                  unreasonably withheld. Notwithstanding the foregoing, in the
                  event that Horizon requests changes in the manufacturing
                  process, AHP shall not be obligated to make such change or
                  conduct any Activities with respect thereto unless the
                  parties mutually agree to make such change in the Product
                  manufacturing process.

         3.2      PROCUREMENT OF MATERIALS. AHP shall use its Commercially
                  Reasonable Efforts to timely procure all Materials necessary
                  for the production of the Products. Title to all such
                  Materials shall reside in AHP. Notwithstanding the foregoing,
                  AHP's obligation to supply Horizon with Product hereunder is
                  subject to AHP's ability to obtain from Third Parties
                  Materials in sufficient quantities to meet Horizon's and
                  AHP's requirements for the manufacture of Products. AHP may,
                  during any period of shortage of any Materials, prorate its
                  supply of such Materials between Horizon and AHP's other uses
                  (e.g., for sales of Products outside of the Territory or use
                  in products other than Products) according to the relative
                  quantities purchased/used by each during the immediately
                  preceding twelve (12) months (or such shorter period of time
                  that AHP has actually been supplying Product to Horizon
                  hereunder if such shortage of Materials occurs prior to the
                  first anniversary of the Effective Date) without regard to
                  price. AHP shall use Commercially Reasonable Efforts to avoid
                  entirely any such shortage or, if avoidance is not possible,
                  to limit such period and amount and shall promptly inform
                  Horizon if it becomes aware of any potential shortage. In the
                  event that, after May 30, 1999, AHP is unable to supply the
                  lesser of seventy-five percent (75%) of (i) the average
                  number of bottles of Product A and Product B sold by Horizon
                  for the previous three full calendar months ("Sale
                  Minimums"), or (ii) 7,600 bottles of Product A and 2,650
                  bottles of Product B ("Bottle Minimums") for a period greater
                  than thirty (30) days, then, provided the shortage has not
                  been resolved prior to the next License Fee payment date,
                  Horizon may reduce or

<PAGE>   10

                  suspend the payment of the amounts otherwise due and payable
                  under Section 4.1 of the License Agreement until AHP is again
                  able to supply Horizon such quantities of Products based on
                  the schedule set forth in Table I below, provided, that in no
                  event shall Horizon reduce or suspend such payments more than
                  two consecutive calendar quarters nor more than three
                  calendar quarters during the eight calendar quarter period
                  specified in Section 4.1(ii) of the License Agreement.

                                    TABLE I
<TABLE>
<CAPTION>

                           AMOUNT OF
                        PRODUCTS SUPPLIED                               PAYMENT REDUCTION
                        -----------------                               -----------------
                        <S>                                             <C>
                        less than 75% but 50%
                        or more of Sale Minimums or                            50%
                        Bottle Minimums, as applicable

                        less than 50% but 25% or more                          75%

                        less than 25%                                    full suspension
</TABLE>

         3.3      REGULATORY FILINGS. Horizon shall provide to AHP copies of
                  all annual reports to the FDA.

         3.4      COMPLIANCE WITH LAWS AND REGULATIONS. While the Products are
                  in its possession or under its control, AHP shall comply with
                  all applicable federal, state and local statutory and
                  regulatory requirements regarding the manufacture, packaging,
                  handling and storage of the Products.

         3.5      PRODUCT COMPLAINTS. Horizon shall be solely responsible for
                  interacting with the public with respect to complaints
                  regarding Product quality. With respect to any such
                  complaints, each Party shall have the responsibility for
                  promptly conducting an investigation of any activities
                  conducted by it under the Transaction Agreements which may be
                  relevant to the complaint and each Party shall promptly
                  report the results of such investigation to the other Party.
                  The Parties shall cooperate in any investigation by the other
                  Party of each such complaint which involves the Parties'
                  duties under this Agreement.

4.       TECHNOLOGY TRANSFER.

         4.1      TRANSFER OF PRODUCT MANUFACTURING KNOW-HOW. As soon as
                  practicable after Horizon's request, and only if Horizon has
                  complied with all of its obligations under the Transaction
                  Agreements including, without limitation, the payment of all
                  fees and payments that become due and payable prior to such
                  time, AHP shall furnish Horizon with one copy of the
                  Know-How, including all technical, manufacturing and AHP's
                  other written information, including but not limited to
                  process sheets, raw material and process specifications,
                  manuals, vendors lists, and other writings specifically
                  relating to the Products, which are currently used by AHP,
                  its Affiliates or sub-contractors to manufacture or have
                  manufactured Products according to the methods used by AHP or
                  its Affiliates or subcontractors. AHP agrees that Horizon,
                  its Affiliates or its permitted sublicensees, may use all
                  Know-How listed in the preceding sentence for the manufacture
                  of Products for sale in the Territory.

<PAGE>   11
                                          [***]-CONFIDENTIAL TREATMENT REQUESTED

         4.2      TRAINING. In connection with the transfer of information
                  described in Section 4.1, AHP shall permit a reasonable
                  number of Horizon's technically skilled personnel and
                  consultants designated by Horizon (with travel and living
                  expenses paid by Horizon) to make one or more visits to such
                  facilities of AHP or its Affiliates as may be engaged in the
                  manufacture of Products for up to an aggregate of thirty (30)
                  man-days in order to inspect and be instructed in all
                  manufacturing techniques and procedures used by AHP, its
                  Affiliates or subcontractors in the manufacture of Products.

         4.3      HORIZON'S USE OF KNOW-HOW. Horizon agrees that it shall use
                  all Know-How provided to Horizon by or on behalf of AHP, its
                  Affiliates or subcontractors pursuant to the Transaction
                  Agreements for the sole purpose of making, using and/or
                  selling the Products only in the Territory and shall not use
                  or permit any Third Party to use such Know-How for the
                  purpose of making Products for sale outside the Territory or
                  for use as veterinary pharmaceutical products within or
                  outside of the Territory. In the event, due to Horizon's
                  failure to comply with any provision of the Transaction
                  Agreements, such Know-How is used for the purpose of making
                  Products for either sale outside the Territory or sale as
                  veterinary pharmaceutical products within or outside of the
                  Territory during such time period, Horizon shall immediately
                  cease such use and/or sale and take such action as may be
                  necessary to prevent a Third Party from using such Know-How
                  for the purpose of making Products for sale outside the
                  Territory and/or for sale as veterinary pharmaceutical
                  products within or outside the Territory. The provisions of
                  this Section shall not limit any other remedy AHP has on
                  account of the use of such Know-How for the purpose of making
                  Products for sale outside the Territory or for sale as
                  veterinary pharmaceutical products within or outside the
                  Territory.

5.       PURCHASE PRICE.

         5.1      PRICE. Horizon shall purchase from AHP and AHP shall sell to
                  Horizon Products at the purchase prices set forth in Schedule
                  5.1 hereof, which purchase prices shall be increased once
                  each year by [****]

         5.2      FREIGHT, INSURANCE AND TAXES. Horizon shall pay all actual
                  freight, insurance and government sales tax imposed on
                  purchasers for resale, and duties and other fees (except tax
                  on income to AHP) incurred in connection with the sale and
                  shipment of the Products to Horizon.

         5.3      PAYMENT. Payments to AHP for the purchase price of delivered
                  Products (as well as any other payment due from Horizon to
                  AHP under this Agreement) shall be made by Horizon within
                  thirty (30) days after the date of invoice, except as to
                  Product orders which are rejected by Horizon in accordance
                  with the procedures recited in Article 6, or which the
                  Parties dispute are in conformance with the Specifications.
                  In the event Product is rejected by Horizon, but is
                  determined to be Acceptable Product pursuant to Section 6.2
                  hereof, the payment for such Product shall be due and payable
                  within ten (10) days after the determination with respect to
                  such Product is made in accordance with Section 6.2 hereof.

<PAGE>   12

         5.4      MAINTENANCE OF RECORDS; AUDITS. AHP shall keep complete
                  records of AHP's Fully Absorbed Costs for the manufacture and
                  supply of Products hereunder, and shall permit an independent
                  certified public accountant selected by Horizon and
                  reasonably acceptable to AHP, at Horizon's expense, at the
                  time of (a) any price adjustment under Section 5.1, or (b)
                  request by AHP for reimbursement of costs incurred under
                  Sections 2.7 and 3.1 hereof, but, in any event, no more than
                  once per year, to inspect and review such records during
                  normal business hours and upon reasonable prior notice, in
                  order to verify or determine such costs and whether an
                  increase in such costs has occurred. The independent
                  certified public accountant may not disclose to Horizon
                  specific manufacturing cost breakdowns, but only whether or
                  not the increase in AHP's Fully Absorbed Cost reported by AHP
                  are correct. Horizon shall bear the costs and fees associated
                  with such inspections and reviews unless it is determined by
                  the independent certified public accountant that such price
                  adjustment was unjustified (in excess of five percent (5%)
                  more than the price increase determined by the independent
                  certified public accountant to be justified), in which case
                  AHP shall bear the costs and fees of such audit and shall
                  promptly refund to Horizon any overpayments made by Horizon
                  because of such unjustified price adjustment.

6.       INSPECTION OF PRODUCT.

         6.1      INSPECTION; REJECTION OF PRODUCT. Horizon shall analyze
                  representative samples of each lot of Product delivered to
                  Horizon for purposes of determining whether the same meets
                  the Specifications and was manufactured in accordance with
                  the NDA and cGMP ("Acceptable Product") and, if performed,
                  will do so within thirty (30) days from the date of delivery
                  of such Products to Horizon's carrier. Horizon shall notify
                  AHP in writing within said thirty (30) days of any of the
                  Product or portion thereof, which Horizon is rejecting
                  because it is not Acceptable Product. If Horizon fails to
                  notify AHP that it is rejecting a lot of Product within such
                  thirty (30) day period, such lot of Product shall be deemed
                  to be Acceptable Product. In the event of a recall of
                  Product, Section 9.1 hereof shall govern.

         6.2      THIRD PARTY ANALYSIS. If AHP, after good faith consultation
                  with Horizon, disputes any finding by Horizon that Product is
                  not Acceptable Product, representative samples of such
                  Product shall be forwarded to a Third Party jointly selected
                  by AHP and Horizon, in their reasonable discretion, for
                  analysis, which analysis shall be performed in compliance
                  with applicable FDA regulations for retesting of
                  pharmaceutical products. The findings of such Third Party
                  regarding whether the Product was Acceptable Product shall be
                  binding upon the Parties. The cost of such analysis by such
                  Third Party shall be borne by the Party whose findings
                  differed from those generated by such Third Party.

         6.3      REPLACEMENT OF PRODUCT. AHP shall replace any Product order,
                  or portion thereof, which is not Acceptable Product (unless
                  such non-conformance is due to any negligent or wrongful act
                  or omission by Horizon or its agents or subcontractors), at
                  its cost and expense, including shipping costs.

<PAGE>   13

         6.4      DISPOSITION OF REJECTED PRODUCT. AHP shall instruct Horizon
                  as to the disposition of any Product order or portion thereof
                  determined not to be Acceptable Product. At the sole option
                  of AHP, said Product may be returned to AHP, at AHP's expense
                  including shipping costs, or destroyed in an environmentally
                  acceptable manner, at AHP's expense.

7.       INSPECTION AND ACCESS TO FACILITY AND RECORDS.

         7.1      INSPECTION BY REGULATORY AUTHORITIES. Upon the request of the
                  FDA or other regulatory agency, such agency shall have access
                  to observe and inspect AHP's or its Affiliates' facilities
                  and procedures used for the manufacture, testing or
                  warehousing of the Products and to audit such facilities for
                  compliance with cGMP and/or other applicable regulatory
                  standards.

         7.2      NOTIFICATION OF INQUIRIES AND INSPECTIONS. AHP also agrees to
                  notify Horizon within ten (10) business days or such shorter
                  time as may be required by the notification of the
                  inspection, of any written or oral inquiries, notifications
                  or inspection activity by the FDA or other regulatory agency
                  in regard to any Product. AHP shall permit not more than two
                  (2) Horizon representatives to attend any such inspections,
                  and shall provide a reasonable description of any such
                  governmental inquiries, notifications or inspections promptly
                  after such visit or inquiry. AHP shall furnish to Horizon (i)
                  within ten (10) business days after receipt, any report or
                  correspondence issued by the FDA or other governmental agency
                  in connection with such visit or inquiry, including but not
                  limited to, any FDA Form 483 (List of Inspectional
                  Observations) or applicable portions of any FDA Warning
                  Letters which pertain to the Products in the Territory and
                  (ii) not later than ten (10) business days prior to the time
                  it provides to the FDA or other regulatory agency, copies of
                  proposed responses or explanations relating to items set
                  forth above (each, a "Proposed Response"), in each case
                  redacted of trade secrets or other confidential or
                  proprietary information of AHP that are unrelated to the
                  obligations under this Agreement or are unrelated to the
                  Products. AHP shall discuss with Horizon and consider in good
                  faith any comments provided by Horizon on the Proposed
                  Response. After the filing of a response with the FDA or
                  other regulatory agency, AHP will notify Horizon of any
                  further contacts with such agency relating to the subject
                  matter of the response.

         7.3      INSPECTION BY HORIZON. AHP shall permit Horizon to inspect
                  once annually that portion of the AHP facility where Product
                  is manufactured and review such Product documents as is
                  reasonably necessary for the purpose of assessing AHP's
                  compliance with applicable regulations. Such inspection and
                  document review shall be conducted upon reasonable prior
                  notice by Horizon, but not less than thirty (30) days prior
                  to the proposed inspection, at a time and date mutually
                  agreeable to the Parties. In addition, in the event Horizon
                  has received two or more shipments of Product determined not
                  to be Acceptable Product pursuant to the procedures of
                  Article VI hereof within a single Calendar Quarter, Horizon
                  shall be permitted to conduct an additional such inspection
                  to help determine the reason(s) for delivery of such
                  non-Accepted Product.

<PAGE>   14

8.       WARRANTIES AND INDEMNITIES.

         8.1      REPRESENTATIONS AND WARRANTIES OF EACH PARTY. As of the
                  Effective Date, each of Horizon and AHP hereby represents,
                  warrants and covenants to the other Party hereto a follows:

                  (a)      it is a corporation or entity duly organized and
                           validly existing under the laws of the state or
                           other jurisdiction of incorporation or formation;

                  (b)      the execution, delivery and performance of this
                           Agreement by such Party has been duly authorized by
                           all requisite corporate action and do not require
                           any shareholder action or approval;

                  (c)      it has the power and authority to execute and
                           deliver this Agreement and to perform its
                           obligations hereunder;

                  (d)      the execution, delivery and performance by such Party
                           of this Agreement and its compliance with the terms
                           and provisions hereof does not and will not conflict
                           with or result in a breach of any of the terms and
                           provisions of or constitute a default under (i) a
                           loan agreement, guaranty, financing agreement,
                           agreement affecting a product or other agreement or
                           instrument binding or affecting it or its property;
                           (ii) the provisions of its charter or operative
                           documents or bylaws; or (iii) any order, writ,
                           injunction or decree of any court or governmental
                           authority entered against it or by which any of its
                           property is bound; and

                  (e)      it shall at all times comply with all applicable
                           material laws and regulations relating to its
                           activities under this Agreement.

         8.2      REPRESENTATIONS AND WARRANTIES OF AHP. In addition to the
                  representations and warranties made by AHP in Section 8.1
                  hereof, AHP hereby represents and warrants to Horizon as
                  follows:

                  (a)      that all Products supplied hereunder conform to the
                           Specifications, will be (and with respect to the
                           initial delivery of Product to Horizon hereunder,
                           were) manufactured in accordance with the applicable
                           Regulatory Approvals and cGMP, and, subject to
                           Section 2.7 hereof, will not be (and, with respect
                           to the initial delivery of Product to Horizon
                           hereunder, were not) adulterated or misbranded while
                           in AHP's possession; and

                  (b)      that it has not and will not use in any capacity the
                           services of any persons debarred under 21 U.S.C.
                           ss.335(a) or 335(b) in connection with the
                           manufacture of the Products.

         8.3      COVENANTS OF HORIZON. In addition to the representations and
                  warranties made by Horizon in Section 8.1 hereof and the
                  covenants made by Horizon elsewhere in this Agreement,
                  Horizon hereby covenants to AHP that it shall not sell the
                  Products manufactured by AHP hereunder in countries other
                  than those within the Territory and that it shall not sell
                  such Products for veterinary use within or outside the
                  Territory. Horizon further covenants that it shall not sell
                  such

<PAGE>   15

                  Products to any Third Party which Horizon has reason to
                  believe might sell the Products in countries other than those
                  within the Territory. In the case of any such Third Party
                  sales, Horizon shall exercise its Commercially Reasonable
                  Efforts, consistent with applicable law, to gain a cessation
                  of such Third Party sales of Products within such countries,
                  including, to the extent possible, terminating its sales of
                  Product to such Third Party.

         8.4      NO OTHER WARRANTIES. EXCEPT FOR THE WARRANTIES EXPRESSLY MADE
                  BY AHP IN SECTIONS 8.1 AND 8.2 HEREOF, AHP MAKES NO OTHER
                  REPRESENTATION OR WARRANTIES, EITHER EXPRESS OR IMPLIED
                  (WHETHER WRITTEN OR ORAL), INCLUDING, WITHOUT LIMITATION, ANY
                  WARRANTY OF MERCHANTABILITY OR ANY WARRANTY OF FITNESS FOR A
                  PARTICULAR PURPOSE WITH RESPECT TO THE PRODUCTS OR AHP'S
                  OBLIGATIONS HEREUNDER. ADDITIONALLY, EXCEPT FOR THE
                  WARRANTIES MADE BY HORIZON IN THIS AGREEMENT, HORIZON MAKES
                  NO OTHER REPRESENTATION OR WARRANTY, EITHER EXPRESS OR
                  IMPLIED (WHETHER WRITTEN OR ORAL) WITH RESPECT TO HORIZON'S
                  OBLIGATIONS HEREUNDER.

         8.5      INDEMNIFICATION BY AHP. AHP shall indemnify, defend and hold
                  harmless Horizon, its Affiliates and their respective
                  officers, directors, shareholders, employees, agents and
                  representatives (each a "Horizon Indemnified Party") from any
                  claims, losses, liabilities, costs, expenses (including
                  reasonable attorney's fees) and damages to Third Parties,
                  including any related to property or personal injury (each a
                  "Liability") which the Horizon Indemnified Party may incur,
                  suffer or be required to pay resulting from or arising in
                  connection with (a) the breach by AHP of any representation
                  or warranty contained in this Agreement; (b) any violation by
                  AHP of any applicable federal, state or local regulation,
                  statute or order in the manufacture and packaging of Products
                  arising out of AHP's duties under this Agreement which is not
                  attributable to printed materials provided by Horizon; or (c)
                  any negligent act or omission by AHP or its affiliates in
                  carrying out its obligations under this Agreement.
                  Notwithstanding the foregoing, AHP shall have no obligations
                  to defend, indemnify or hold harmless any Horizon Indemnified
                  Party for any Liability that results from the negligence or
                  intentional misconduct of Horizon, its Affiliates, or any of
                  its permitted sublicensees or any of their respective
                  officers, directors, employees, agents, consultants or
                  representatives.

         8.6      INDEMNIFICATION BY HORIZON. Horizon shall indemnify, defend
                  and hold harmless AHP and its Affiliates, and each of its and
                  their respective employees, officers, directors and agents
                  (each, an "AHP Indemnified Party") from and against any
                  Liability which the AHP Indemnified Party may incur, suffer
                  or be required to pay resulting from or arising in connection
                  with (a) the breach by Horizon of any representation or
                  warranty contained in this Agreement; (b) materials or
                  promotional claims (except to the extent that AHP has
                  previously reviewed and approved the specific material or
                  promotional claim under Section 8.2 of the License
                  Agreement), (c) the manufacture, packaging, promotion,
                  distribution, testing, use, marketing, sale or other
                  disposition of Products by Horizon, its Affiliates, its
                  permitted sublicensees or their respective subcontractors; or
                  (d) the use of the Trademark by Horizon, its Affiliates, its

<PAGE>   16

                  permitted sublicensees or their respective subcontractors.
                  Notwithstanding the foregoing, Horizon shall have no
                  obligations to indemnify, defend, or hold harmless any AHP
                  Indemnified Party for any Liability that results from the
                  international misconduct or negligence of AHP, its
                  Affiliates, its permitted sublicensees or any of their
                  respective employees, officers, directors or agents,
                  consultants or representatives.

         8.7      CONDITIONS TO INDEMNIFICATION. The obligations of the
                  indemnifying Party under Sections 8.5 and 8.6 are conditioned
                  upon the delivery of written notice to the indemnifying Party
                  of any potential Liability promptly after the indemnified
                  Party becomes aware of such potential Liability. The
                  indemnifying Party shall have the right to assume the defense
                  of any suit or claim relating to the Liability if it has
                  assumed responsibility for the suit or claim in writing;
                  however, if in the reasonable judgment of the indemnified
                  Party, such suit or claim involves an issue or matter which
                  could have a materially adverse effect on the business
                  operations or assets of the indemnified Party, the
                  indemnified Party may waive its rights to indemnity under
                  this Agreement and control the defense or settlement thereof,
                  but in no event shall any such waiver be construed as a
                  waiver of any indemnification rights such Party may have at
                  law or in equity. If the indemnifying Party defends the suit
                  or claim, the indemnified Party may participate in (but not
                  control) the defense thereof at its sole cost and expense.

         8.8      SETTLEMENTS. Neither Party may settle a claim or action
                  related to a Liability without the consent of the other
                  Party, if such settlement would impose any monetary
                  obligation on the other Party or require the other Party to
                  submit to an injunction or otherwise limit the other Party's
                  rights under this Agreement. Except as otherwise expressly
                  set forth in this Article 8, any payment made by a Party to
                  settle any such claim or action shall be at its own cost and
                  expense.

         8.9      LIMITATION OF LIABILITY. With respect to any claim by one
                  Party against the other arising out of the performance or
                  failure of performance of the other Party under this
                  Agreement, the Parties expressly agree that the liability of
                  such Party to the other Party for such breach shall be
                  limited under this Agreement or otherwise at law or equity to
                  direct damages only and in no event shall a Party be liable
                  for, punitive, exemplary or consequential damages. The
                  limitations set forth in this Section 8.9 shall not apply
                  with respect to the obligations of either Party to indemnify
                  the other under Sections 8.5 or 8.6 hereof in connection with
                  a Liability to a third party.

         8.10     INSURANCE. Horizon shall obtain and maintain at all times
                  during the term of this Agreement Commercial General
                  Liability Insurance, including Products Liability, with
                  limits of liability of not less than Five Million Dollars
                  ($5,000,000) per occurrence and Ten Million Dollars
                  ($10,000,000) in the aggregate. Horizon shall provide AHP
                  with a Certificate of Insurance evidencing this coverage
                  within thirty (30) days of the Effective Date. Such insurance
                  policy shall name AHP as an additional insured and Horizon
                  shall use its Commercially Reasonable Efforts to ensure such
                  insurance policy contains a provision requiring ten (10) day
                  advance notification to AHP in the event of its cancellation
                  or termination. AHP shall maintain self insurance and/or
                  insurance obtained from Third Party insurers in amounts
                  sufficient to cover its obligations under Section 8.5. Upon
                  Horizon's written request, AHP shall provide Horizon with
                  evidence of such insurance coverage.

<PAGE>   17

9.       RECALLS.

         9.1      PRODUCT RECALLS. In the event of an actual or threatened
                  recall of any Product required or recommended by a
                  governmental agency or authority of competent jurisdiction
                  within the Territory or if recall of any Product is (i)
                  reasonably deemed advisable by AHP or by Horizon, or (ii)
                  jointly deemed advisable by AHP and Horizon, such recall
                  shall be promptly implemented and administered by Horizon in
                  a manner which is appropriate and reasonable under the
                  circumstances and in conformity with accepted trade
                  practices. In the event that a recall is caused because, due
                  to negligent acts or omissions of AHP, its Affiliates or
                  subcontractors, Product supplied by AHP to Horizon does not
                  conform to the Specifications or was not manufactured in
                  accordance with the applicable Regulatory Approvals and cGMP,
                  the cost, including Horizon's reasonable out-of-pocket
                  expenses, of any such recall shall be borne by AHP. Horizon
                  shall pay all costs, including AHP's reasonable out-of-pocket
                  expenses, associated with a recall for any other reason,
                  including without limitation, recalls (i) caused by actions
                  of Third Parties occurring after such Product is sold by
                  Horizon, (ii) due to packaging or label defects for which
                  Horizon has responsibility or (iii) due to any other breach
                  by Horizon of its duties under this Agreement.

         9.2      NOTICE OF EVENTS THAT MAY LEAD TO PRODUCT RECALL. Each Party
                  shall keep the other fully and promptly informed of any
                  notification, event or other information, whether received
                  directly or indirectly, which might affect the marketability,
                  safety or effectiveness of Products or might result in a
                  recall of Products by the FDA.

         9.3      RECALL DUE TO BREACH BY AHP. In the event of any recall for
                  which AHP would be responsible for the costs in accordance
                  with Section 9.1 hereof, AHP shall, at the election of
                  Horizon either:

                  (a)      supply Products, without charge to Horizon, in an
                           amount sufficient to replace the amounts of Products
                           recalled, or

                  (b)      refund to Horizon or give credit to Horizon against
                           outstanding receivables due from Horizon for the
                           price of Products to be delivered to Horizon in the
                           future, in amounts equal to the price paid by
                           Horizon to AHP for Products so recalled plus the
                           reasonable transportation costs incurred by Horizon
                           and not recovered by Horizon in respect of such
                           recalled Products.

                  In addition, if, as a direct result of any recall for which
                  AHP would be responsible for the costs in accordance with
                  Section 9.1 hereof, Horizon's aggregate sales of Products in
                  any consecutive thirty (30) day period fall below fifty
                  percent (50%) of Horizon's average monthly sales of Products
                  for the preceding six (6) months, then Horizon may postpone
                  payment of the first and second payments following the recall
                  otherwise due and payable under Section 4.1(ii) of the
                  License agreement for six (6) months, after which Horizon
                  shall resume making such payments, including immediate
                  payment of the two postponed payments.

<PAGE>   18
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

         9.4      DEFINITION OF RECALL. For Purposes of this Article 9,
                  "recall" shall mean any action by Horizon and its Affiliates,
                  or AHP and its Affiliates, to recover title or possession or
                  halt distribution, prescription or consumption of Products
                  sold or shipped to Third Parties. The term "recall" also
                  applies to Product which would have been subject to recall if
                  it had been sold or shipped.

         9.5      SURVIVAL OF OBLIGATIONS. The provisions and obligations of
                  this Article 9 shall survive any termination of this
                  Agreement.

10.      TERM AND TERMINATION.

         10.1     TERM. This Agreement shall become effective upon the
                  Effective Date of the License Agreement and, unless earlier
                  terminated as provided below, shall remain in full force and
                  effect for a period ending on the second (2nd) anniversary of
                  the Effective Date (the "Term"). Thereafter, the term of this
                  Agreement may be extended by Horizon on six (6) months' prior
                  written notice for up to six (6) additional months provided
                  that the Parties agree upon all terms and conditions of such
                  extension not later than the expiration of the Term. The
                  Supply Price would be negotiated but shall not be less than
                  AHP's Fully Absorbed Cost plus a [***] percent [***] mark-up.
                  If the Parties have not extended the term of this Agreement or
                  signed a new supply agreement before the expiration of the
                  Term, AHP shall have no obligation to supply Horizon with any
                  Product after expiration of the Term. Upon expiration or
                  termination of this Agreement for any reason, all unpaid
                  amounts due pursuant to Section 5.1 shall become immediately
                  due and payable.

         10.2     TERMINATION BY AHP. AHP may terminate this Agreement, except
                  as limited hereinafter, immediately upon written notice, in
                  the event

                  (a)      Horizon fails to make any payment due and owing
                           within thirty (30) days after notice thereof from
                           AHP that such payment has not been made by Horizon
                           by the date specified in Section 5.3; or

                  (b)      Horizon commits a breach of any material provision
                           of this Agreement which breach remains uncured for
                           sixty (60) days, measured from the date written
                           notice of such breach is given to Horizon, or if
                           such breach is not susceptible of cure within such
                           sixty (60) day period and Horizon uses good faith
                           efforts to cure such breach, for one hundred eighty
                           (180) days after written notice to Horizon; or

`                 (c)      the License Agreement is terminated for any reason,
                           other than AHP's breach of the License Agreement,
                           prior to the expiration of the Term of this
                           Agreement.

         10.3     TERMINATION BY HORIZON. Horizon may terminate this Agreement,
                  in whole or with regard to a specific Product as applicable,
                  immediately upon written notice in the event (a) AHP commits
                  a breach of any material provision of this Agreement, which
                  is not cured within thirty (30) days in case of a failure to
                  make any payment due and owing; or (b) AHP commits a breach
                  of any material provision of this Agreement which breach
                  remains uncured for sixty (60) days, measured from the date
                  written notice of such breach is given to AHP, or if such
                  breach is not susceptible of cure within such sixty (60) day
                  period and AHP uses good faith efforts to cure such breach,
                  for one hundred eighty (180) days after written notice to
                  AHP; or (c) the License Agreement is terminated for any
                  reason other than Horizon's breach of the License Agreement
                  prior to the expiration of the Term of this Agreement.

<PAGE>   19

         10.4     INSOLVENCY. Either party may terminate this Agreement upon
                  the filing or institution of bankruptcy, reorganization,
                  liquidation or receivership proceedings, or upon an
                  assignment of a substantial portion of the assets for the
                  benefit of creditors by the other Party, or in the event a
                  receiver or custodian is appointed for such party's business,
                  or if a substantial portion of such Party's business is
                  subject to attachment or similar process; provided, however,
                  that in the case of any involuntary bankruptcy proceeding
                  such right to terminate shall only become effective if the
                  proceeding is not dismissed within ninety (90) days after the
                  filing thereof.

         10.5     EFFECT OF TERMINATION. Upon termination or expiration of this
                  Agreement, except in the event of termination of the
                  Agreement by AHP pursuant to Sections 10.2 or 10.4, AHP shall
                  have the obligations set forth in Sections 4.1 and 4.2. If
                  AHP terminates this Agreement pursuant to either Section 10.2
                  or 10.4, the obligations set forth in Sections 4.1 and 4.2
                  hereof shall survive termination if Horizon has made or
                  accelerates payment of all payments to AHP required under
                  Section 4.1 of the License Agreement, and otherwise the
                  obligations under Sections 4.1 and 4.2 hereof shall not
                  survive termination. In the event that Horizon terminates
                  this Agreement pursuant to Section 10.3 hereof because of a
                  failure to supply Product to Horizon which failure to supply
                  results in an uncured breach of this Agreement by AHP,
                  Horizon shall thereafter be permitted to manufacture Product
                  either directly or through a Third Party and the transfer of
                  manufacturing Know-How under Section 4.1 shall be
                  accomplished as soon as practicable, but in no event more
                  than thirty (30) days, after this Agreement is so terminated
                  and the reasonable out-of-pocket costs incurred by the
                  Parties in transferring such Product manufacturing
                  responsibilities from AHP to either Horizon, its Affiliates
                  or a Third Party shall be borne by AHP.

         10.6     ACCRUED OBLIGATIONS. Termination of this Agreement for any
                  cause shall not release either Party from any obligation
                  theretofore accrued.

         10.7     NO WAIVER. The failure on the part of either Party to
                  exercise or enforce any right conferred upon it hereunder
                  shall not be deemed to be a waiver of any such right nor
                  operate to bar the exercise or enforcement thereof at any
                  time thereafter.

         10.8     OUTSTANDING ORDERS. Upon termination of this Agreement for
                  any reason other than pursuant to Sections 10.2 or 10.5
                  hereof, AHP shall fill all outstanding purchase orders of
                  Horizon or its Affiliates for the Products, unless otherwise
                  instructed by Horizon.

         10.9     BULK SUBSTANCE. To the extent permitted under the supply
                  agreement planned to be entered into between AHP and its
                  supplier of Substance (the "Bulk Substance Supply
                  Agreement"), AHP will use commercially reasonable efforts to
                  have such supplier enter into a direct supply agreement for
                  Substance with Horizon upon expiration of this Agreement, on
                  the same terms and conditions, including price, as the Bulk
                  Substance Supply Agreement. AHP shall not be required, as
                  part of its commercially reasonable efforts, to pay any money
                  or provide any other form of consideration to such supplier.
                  Upon expiration of this Agreement, if such direct supply
                  agreement is not entered into, AHP and Horizon will cooperate
                  in a mutually agreeable arrangement under which to the extent
                  feasible Horizon would obtain the benefits and assume the
                  obligations of AHP under the Bulk

<PAGE>   20

                  Substance Supply Agreement as it relates to Substance,
                  including subcontracting to Horizon, or under which AHP would
                  enforce for the benefit of Horizon, with Horizon assuming
                  AHP's obligations, any and all rights of AHP against such
                  supplier. The purpose of such an arrangement would be for
                  Horizon to obtain price, quantity, destination and delivery
                  date terms comparable to AHP's rights under the Bulk
                  Substance Supply Agreement.

         10.10    SURVIVAL. Subject to Section 10.5 hereof, the following
                  provisions shall survive expiration or termination of this
                  Agreement: Sections 2.8, 3.3, 4.1, 4.2, 4.3, 5.4, 10.9,
                  10.10, 12.6 and 12.7 and Articles 8, 9 and 11.

11.      CONFIDENTIALITY.

         11.1     NONDISCLOSURE OBLIGATION.  Each of Horizon and AHP shall use
                  only in accordance with this Agreement and shall not disclose
                  to any Third Party any information including, without
                  limitation, Know-How, received by it from the other Party
                  (the "Information"), without the prior written consent of the
                  other Party. The foregoing obligations shall survive the
                  expiration or earlier termination of the last of the
                  Transaction Agreements to so expire or to be so terminated
                  for a period of five (5) years. These obligations shall not
                  apply to Information that:

                           (i)      is known by the receiving Party at the time
                                    of its receipt, and not through a prior
                                    disclosure by the disclosing Party, as
                                    documented by business records;

                           (ii)     is at the time of disclosure or thereafter
                                    becomes published or otherwise part of the
                                    public domain without breach of this
                                    Agreement by the receiving Party;

                           (iii)    is subsequently disclosed to the receiving
                                    Party by a Third Party who has the right to
                                    make such disclosure;

                           (iv)     is developed by the receiving Party
                                    independently of the Information received
                                    from the disclosing Party and such
                                    independent development can be documented
                                    by the receiving Party; or

                           (v)      is required by law, regulation, rule, act or
                                    order of any governmental authority or
                                    agency to be disclosed by a Party, provided
                                    that notice is promptly delivered to the
                                    other Party in order to provide an
                                    opportunity to seek a protective order or
                                    other similar order with respect to such
                                    Information and thereafter the disclosing
                                    Party discloses to the requesting entity
                                    only the minimum Information required to be
                                    disclosed in order to comply with the
                                    request, whether or not a protective order
                                    or other similar order is obtained by the
                                    other Party.

         11.2     PERMITTED DISCLOSURES. Information may be disclosed to
                  employees, agents, consultants, sublicensees or suppliers of
                  the recipient Party or its Affiliates, but only to the extent
                  required to accomplish the purposes of this Agreement and

<PAGE>   21

                  only if the recipient Party obtains prior agreement from its
                  employees, agents, consultants, sublicensees, suppliers or
                  Third Party manufacturers to whom disclosure is to be made to
                  hold in confidence and not make use of such Information for
                  any purpose other than those permitted by this Agreement.
                  Each Party will use at least the same standard of care as it
                  uses to protect proprietary or confidential information of
                  its own to ensure that such employees, agents, consultants,
                  sublicensees, suppliers or Third Party manufacturers do not
                  disclose or make any unauthorized use of the Information.

         11.3     DISCLOSURE OF AGREEMENT. Neither Horizon nor AHP shall
                  release to any Third Party or publish in any way any
                  non-public information with respect to the terms of this
                  Agreement or concerning their cooperation without the prior
                  written consent of the other, which consent will not be
                  unreasonably withheld or delayed, provided, however, that
                  either Party may disclose the terms of this Agreement to the
                  extent required to comply with applicable laws, including,
                  without limitation, the rules and regulations promulgated by
                  the United States Securities and Exchange Commission,
                  provided, however, that prior to making any such disclosure,
                  the Party intending to so disclose the terms of this
                  Agreement shall (i) provide the nondisclosing Party with
                  written notice of the proposed disclosure and an opportunity
                  to review and comment on the intended disclosure which is
                  reasonable under the circumstances and (ii) shall seek
                  confidential treatment for as much of the disclosure as is
                  reasonable under the circumstances, including, without
                  limitation, seeking confidential treatment of any information
                  as may be requested by the other Party. Notwithstanding any
                  other provision of this Agreement, each Party may disclose
                  the terms of this Agreement to lenders, investment bankers
                  and other financial institutions of its choice solely for
                  purposes of financing the business operations of such Party
                  either (i) upon the written consent of the other Party or
                  (ii) if the disclosing Party uses reasonable efforts to
                  obtain a signed confidentiality agreement with such financial
                  institution with respect to such information on terms
                  substantially similar to those contained in this Article 11.

         11.4     PUBLICITY. Subject to Section 11.3, all publicity, press
                  releases and other announcements relating to this Agreement
                  or the transactions contemplated hereby shall be reviewed in
                  advance by, and shall be subject to the approval of, both
                  Parties. The Party responding to a request for such approval
                  shall respond to the other Party in writing within five (5)
                  days of such request.

         11.5     WAIVER. AHP agrees that, upon AHP and its supplier of
                  Substance entering into the Bulk Substance Supply Agreement,
                  AHP shall waive its rights under the Confidentiality
                  Agreement among AHP, Horizon, EJ Financial and Mikart, the
                  License Agreement and this Agreement to the extent such
                  agreements prohibit Horizon from communicating with such
                  supplier and entering into agreement(s) regarding the
                  Substance with such supplier.

12.      MISCELLANEOUS.

         12.1     FORCE MAJEURE. Neither Party shall be liable to the other for
                  delay or failure in the performance of the obligations on its
                  part contained in this Agreement if and to the extent that
                  such failure or delay is due to circumstances beyond its
                  control (including, without limitation, AHP's inability to
                  obtain, from a Third Party,

<PAGE>   22

                  sufficient quantities of the raw materials needed for the
                  manufacture of Substance to meet its manufacturing
                  obligations hereunder) which it could not have avoided by the
                  exercise of reasonable diligence. It shall notify the other
                  Party promptly should such circumstances arise, giving an
                  indication of the likely extent and duration thereof, and
                  shall use all Commercially Reasonable Efforts to resume
                  performance of its obligations as soon as practicable.

         12.2     ASSIGNMENT.

                  12.2.1   ASSIGNMENT BY HORIZON. Horizon may assign any or all
                           of its right or obligations under this Agreement in
                           the Territory to any of its Affiliates, for so long
                           as they remain Affiliates. In addition, Horizon may
                           assign any or all of its rights or obligations under
                           this Agreement in the Territory in conjunction with
                           a merger or acquisition of Horizon. Horizon may not
                           otherwise assign any of its rights or obligations
                           under this Agreement without AHP's prior written
                           consent, which consent shall not be unreasonably
                           withheld. AHP shall respond to such requests by
                           Horizon for assignment within thirty (30) days from
                           such request. Any permitted assignment shall not
                           relieve Horizon of its responsibilities for
                           performance of its obligations under this Agreement.

                  12.2.2   ASSIGNMENT BY AHP. AHP may assign any or all of its
                           rights or obligations under this Agreement to any of
                           its Affiliates or to any Third Party, provided,
                           however, that AHP may assign all or part of its
                           obligations to a Third Party only after receiving
                           Horizon's prior written consent, which consent shall
                           not be unreasonably withheld or delayed; provided,
                           further, that such assignment shall not relieve AHP
                           of its responsibilities for performance of its
                           obligations under this Agreement. Notwithstanding
                           the foregoing, Horizon's consent shall not be
                           required for any assignment made by AHP in
                           connection with a merger or similar reorganization
                           of AHP or its parent company or the sale of all or
                           substantially all of AHP's or AHP's parent company's
                           pharmaceutical assets.

                  12.2.3   BINDING NATURE OF ASSIGNMENT. This Agreement shall
                           be binding upon and inure to the benefit of the
                           successors and permitted assigns of the Parties. Any
                           assignment not in accordance with this Section 12.2
                           shall be void.

         12.3     NO WAIVER. The failure of either Party to require performance
                  by the other Party of any of that other Party's obligations
                  hereunder shall in no manner affect the right of such Party
                  to enforce the same at a later time. No waiver by any Party
                  hereto of any condition, or of the breach of any provision,
                  term, representation or warranty contained in this Agreement,
                  whether by conduct or otherwise, in any one or more
                  instances, shall be deemed to be or construed as a further or
                  continuing waiver of any such condition or breach, or of any
                  other condition or of the breach of any other provision,
                  term, representation or warranty hereof.

         12.4     SEVERABILITY. If a court or other tribunal of competent
                  jurisdiction should hold any term or provision of this
                  Agreement to be excessive, or invalid, void or unenforceable,
                  the offending term or provision shall be deleted or revised
                  to the

<PAGE>   23

                  extent necessary to be enforceable, and, if possible,
                  replaced by a term or provision which, so far as practicable,
                  achieves the legitimate aims of the Parties.

         12.5     RELATIONSHIP BETWEEN THE PARTIES. Both Parties are
                  independent contractors under this Agreement. Nothing herein
                  contained shall be deemed to create an employment, agency,
                  joint venture or partnership relationship between the Parties
                  hereto or any of their agents or employees, or any other
                  legal arrangement that would impose liability upon one party
                  for the act or failure to act of the other Party. Neither
                  Party shall have any express or implied power to enter into
                  any contracts or commitments or to incur any liabilities in
                  the name of, or on behalf of, the other Party, or to bind the
                  other Party in any respect whatsoever.

         12.6     CORRESPONDENCE AND NOTICES.

                  12.6.1   ORDINARY NOTICES. Correspondence, reports,
                           documentation, and any other communication in
                           writing between the Parties in the course of
                           ordinary implementation of this Agreement shall be
                           delivered by hand, sent by facsimile, overnight
                           courier or by airmail to the employee or
                           representative of the other Party who is designated
                           by such other Party to receive such written
                           communication.

                  12.6.2   EXTRAORDINARY NOTICES. Extraordinary notices and
                           communications (including, without limitation,
                           notices of termination, force majeure, material
                           breach, change of address) shall be in writing and
                           sent by prepaid registered or certified air mail, or
                           by facsimile confirmed by prepaid registered or
                           certified air mail letter, and shall be deemed to
                           have been properly served to the addressee upon
                           receipt of such written communication.

                  12.6.3   ADDRESSES. In the case of Horizon, the proper
                           address for communications and for all payments
                           shall be:

                                    Horizon Pharmaceutical Corporation
                                    660 Hembree Parkway, Suite 106
                                    Roswell, Georgia  30076
                                    Attn:  Mr. Brent Dixon
                                    Fax:  (770) 442-9594

                           and in the case of AHP, the proper address for
                           communications and for all payments shall be:

                                    Wyeth-Ayerst Laboratories
                                    555 Lancaster Avenue
                                    St. Davids, Pennsylvania  19087
                                    Attn:  Senior Vice President, Global
                                           Business Development
                                    Fax:  (610) 688-9498

                           with a copy to:

                                    American Home Products Corporation
                                    5 Giralda Farms

<PAGE>   24

                                    Madison, New Jersey  07940
                                    Attn: Senior Vice President and General
                                          Counsel
                                    Fax: (973) 660-7156

         12.7     CHOICE OF LAW. This Agreement is subject to and governed by
                  the laws of the State of Delaware, excluding its conflict of
                  law provisions.

         12.8     ENTIRE AGREEMENT; AMENDMENT. This Agreement, together with
                  the other Transaction Agreements and the Confidential
                  Disclosure Agreement between AHP and E.J. Financial
                  Enterprises Inc. (an equity holder in Horizon) dated April
                  28, 1998, and all the covenants, promises, agreements,
                  warranties, representations, conditions and understandings
                  contained herein and therein sets forth the complete, final
                  and exclusive agreement between the Parties and supersedes
                  and terminates all prior and contemporaneous agreements and
                  understandings between the Parties, whether oral or in
                  writing. There are no covenants, promises, agreements,
                  warranties, representations, conditions or understandings,
                  either oral or written, between the Parties other than as are
                  set forth in the Transaction Agreements. No subsequent
                  alteration, amendment, change, waiver or addition to this
                  Agreement shall be binding upon the Parties unless reduced to
                  writing and signed by an authorized officer of each Party. No
                  understanding, agreement, representation or promise, not
                  explicitly set forth herein, has been relied on by either
                  Party in deciding to execute this Agreement.

         12.9     HEADINGS. The headings and captions used in this Agreement
                  are solely for the convenience of reference and shall not
                  affect its interpretation.

         12.10    COUNTERPARTS. This Agreement may be executed in one or more
                  counterparts each of which shall be an original and all of
                  which shall constitute together the same document.

         12.11    FURTHER ACTIONS. Each Party agrees to execute, acknowledge
                  and deliver such further instruments, and to do all other
                  acts, as may be necessary or appropriate in order to carry
                  out the purposes and intent of this Agreement including,
                  without limitation, any filings with any antitrust agency
                  which may be required.

         IN WITNESS WHEREOF, this Agreement has been executed by the duly
authorized representatives of the Parties as of the date set forth below.

AMERICAN HOME PRODUCTS CORPORATION          HORIZON PHARMACEUTICAL CORPORATION

By:                                         By:
   ---------------------------------           ---------------------------------
Name:                                       Name:
     -------------------------------             -------------------------------
Title:                                      Title:
      ------------------------------              ------------------------------

<PAGE>   25
                                  SCHEDULE 1.19

                                 SPECIFICATIONS

         PRODUCT SPECIFICATIONS ARE SET FORTH ON THE FOLLOWING 22 PAGES

<PAGE>   26

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                           GENERAL PRODUCT INFORMATION

LABEL CLAIM:                                         Glycopyrrolate,  [***]

DOSAGE FORM:                                         [***]

LOT SIZE:                                            [***]

PACKAGE SIZE:                                        [***]

PRODUCT CODE:                                        7824

NDA NO.:                                             [***]

RX OR OTC:                                           Rx

OFFICIAL NF OR USP:                                  [***]

DEA CLASS:                                           [***]

FORM 6 NO.:                                          [***]

EXPIRATION DATE:                                     3 years

MFD. BY:                                             A. H. Robins Company

                                TABLE OF CONTENTS

PAGE 2 - GENERAL PRODUCT INFORMATION

PAGE 3 - IN-PROCESS - DURING COMPRESSION

PAGE 7 - BULK FINISHED PRODUCT - AFTER COMPRESSION

PAGE 17 - REGULATORY SPECIFICATIONS AND METHODS

PAGE 19 - PACKAGED PRODUCT SPECIFICATIONS AND TEST PROCEDURES

<PAGE>   27
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                                AFTER COMPRESSION

SAMPLING

This sample is the composite of in-process samples collected during the
compression of the lot and shall consist of at least [***] tablets.

TESTS

<TABLE>
         <S>                                <C>
         Description
         ------------

                  Specification:            A white, round, flat-face, beveled-edge, compressed tablet, [***] mm
                                            in diameter and [***] mm thick.  One side is engraved [***] - 7824, the
                                            obverse side is scored.  Odor shall be characteristic of product.

                  Test:                     [***]

         Weight (Average of [***] Tablets)
         ---------------------------------

                  Specification:            Theoretical average weight          [***]
                                            Acceptable range                    [***]

                  Test:                     Record the average tablet weight of [***] tablets as determined from
                                            [***].

         Dissolution - Glycopyrrolate
         ----------------------------

                  Specification:            [***]

                  Principle                 [***]

                  Reagants                  [***]

                  Calculation               [***] glycopyrrolate [***]
</TABLE>

Discussion

Start-up and Shut-down of System

Assay-Glycopyrrolate

         [***]

<PAGE>   28
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                  Specification:            [***]

                  Reagants:                 [***]

                                            glycopyrrolate  [****]

                                            glycopyrrolate  [****]

                  Procedure                 [***]

                  Calculation               [***]  glycopyrrolate  [****]

                                            [***]

                  Calculation               [***] glycopyrrolate [****]

                  Calculation               [***] glycopyrrolate [***]

         Discussion

         Start-up and Shut-down of System

         Assay - Glycopyrrolate

                  Specification:            [***]

                  Reagents                  [***]

                                            glycopyrrolate [****]

                                            glycopyrrolate [****]

                  Procedure                 [***]

                  Calculation               [***] glycopyrrolate [****]

         Glycopyrrolate Identification

         [****]  glycopyrrolate [****]

Uniformity of Dosage Units

<PAGE>   29
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

         Method:                    [***]

         Specification:             [***]
<PAGE>   30

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

         Test:                              [***]

                           Principles       [***]

                           Apparatus        [***]

                           Reagents         [***]

                                            gylcopyrrolate [****]

                           Procedure        1.       [***]
                                            2.       [***]
                                            3.       [***]

                           Calculation               [***]

<PAGE>   31
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

            BULK FINISHED PRODUCT SPECIFICATIONS AND TEST PROCEDURES

                      [****] GLYCOPYRROLATE ROBINS PRODUCT

                              PRODUCT GRAPH OMITTED

<PAGE>   32

                           PRODUCT SCAN GRAPH OMITTED

<PAGE>   33
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

ACCEPT/REJECT

[***]

1.       [***]

2.       [***]

<PAGE>   34
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

INSPECTION

During the packaging of the product at A. H. Robins Company, the
following [***].

PRODUCT IDENTIFICATION

[***]

SHELF SAMPLE

[***]

NET CONTENTS OF CONTAINERS

         Specification:           [***]

         Test:                    [***]

BOTTLES AND CAPS

         Specification:           Complies with standard

         Test:                    Each bottle sampled shall be examined for the
                                   following:

                                  1.       [***]
                                  2.       [***]
                                  3.       [***]
                                  4.       [***]
                                  5.       [***]
                                  6.       [***]
                                  7.       [***]

<PAGE>   35
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

<TABLE>
<S>                                         <C>
LABELS
         Specification:                     Complies with standard

         Test:                              The label of each bottle sampled shall be examined for the following:

                                            1.       [***]
                                            2.       [***]
                                            3.       [***]
                                            4.       [***]
                                            5.       [***]

CARTONS

         Specification:                     Complies with standard

         Test:                              Each carton sampled shall be examined for the following:

                                            1.       [***]
                                            2.       [***]
                                            3.       [***]
                                            4.       [***]
                                            5.       [***]

INSERTS

         Specification:                     Complies with standard

         Test:                              The insert of each bottle sampled shall be examined for the following:

                                            1.       [***]
                                            2.       [***]
                                            3.       [***]
                                            4.       [***]
</TABLE>

<PAGE>   36
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

STANDARDS

[***] by the A.H. Robins Company. [****] by the A.H. Robins Company [****]

ACCEPT/REJECT

[***]

1.       [***]

2.       [***]

Specification Approved                               May, 1990

Robert W. Alexander, Jr.                       A. Edwin Martin
Director, Quality Assurance                    Vice President, GMP
A. H. Robins Company                           A. H. Robins Company

--------------------------------               --------------------------------

<PAGE>   37

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                                     GRAPHIC
                                    WHITEHALL
                                     ROBINS

                                WHITEHALL ROBINS
                      ANALYTICAL DEVELOPMENT - TEST METHOD

Method:                    [***] Glycopyrrolate [****] Glycopyrrolate

WH#/Product:               [***]

Method#:                   [***]

Date:

Supersedes:                [***]

Developed by:              [***]

Checked by:

Reviewed by:

<PAGE>   38
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

-------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                                       Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

COMPOSITE ASSAY FOR GLYCOPYRROLATE                            [***]

Reagents

Glycopyrrolate - Whitehall Robins [***]

Apparatus

[***]

Preparation of Standard Solution

NOTE:  Prepare this solution fresh daily.

1.       [***]

2.       [***]

3.       [***]

4.       [***]

                                     1 of 7
<PAGE>   39
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

-------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
-------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                     Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

Preparation of Sample Solution

1.       [***] glycopyrrolate [****] glycopyrrolate [***]

2.       [***]

3.       [***]

4.       [***]

5.       [***]

Procedure

1.       [***]

2.       [***]

3.       [***]

4.       [***]

5.       [***]

                                     2 of 7
<PAGE>   40
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

--------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------
                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                    Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

6.       [***]

7.       [***] glycopyrrolate [****]

Manual Calculations
[***] glycopyrrolate [****]
      glycopyrrolate [****]

                                     3 of 7
<PAGE>   41
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

--------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                      Date:    [***]

Method#: [***]                                           Supersedes:      [***]

                            PRODUCT EQUATION OMITTED

where:

         Au       =        absorbance of sample
         As       =        absorbance of standard
         Ws       =        weight of standard, in mg
         n        =        number of tablets used

CONTENT UNIFORMITY FOR GLYCOPYRROLATE       [***]

Reagents

Refer to section under [***]Glycopyrrolate".

Apparatus

Refer to section under [***]Glycopyrrolate."

Preparation of Standard Solution

Refer to section under [***]Glycopyrrolate."

                                     4 of 7
<PAGE>   42
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

--------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                       Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

Preparation of Sample Solution

1.       [***]

2.       [***]

3.       [***]

4.       [***]

Procedure

Refer to section under [***]Glycopyrrolate."

Manual Calculations

[***] glycopyrrolate [****]

For [***] tablets:

                            PRODUCT EQUATION OMITTED

                                     5 of 7

<PAGE>   43
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

            BULK FINISHED PRODUCT SPECIFICATIONS AND TEST PROCEDURES

--------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                     Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

                            PRODUCT EQUATION OMITTED

For [****] tablets:

                            PRODUCT EQUATION OMITTED

                                     6 of 7
<PAGE>   44

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

            BULK FINISHED PRODUCT SPECIFICATIONS AND TEST PROCEDURES

--------------------------------------------------------------------------------
GRAPHIC                    ANALYTICAL DEVELOPMENT - TEST METHOD
--------------------------------------------------------------------------------

                     Robinul Tablets, Robinul Forte Tablets
WH#:     [***]                       Date:    [***]

Method#: [***]                                           Supersedes:      [***]
--------------------------------------------------------------------------------

                            PRODUCT EQUATION OMITTED

where:

         Au       =        absorbance of sample
         As       =        absorbance of standard
         Ws       =        weight of standard, in mg

                                     7 OF 7
<PAGE>   45
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

            BULK FINISHED PRODUCT SPECIFICATIONS AND TEST PROCEDURES

                                  SCHEDULE 5.1

                             INITIAL PURCHASE PRICES

<TABLE>
<CAPTION>

Product           Strength          Package Size            AHP NDC#               Initial Purchase Price
-------           ---------         ------------            --------               ----------------------
<S>               <C>               <C>                     <C>                    <C>
Robinul tablets   1 mg              bottles of 100          7824-63                       $ [***]
Robinul tablets   2 mg              bottles of 100          7840-63                       $ [***]
Robinul tablets   2 mg                 bulk                   N/A                         $ [***] per [***]
Robinul tablets   2 mg                 bulk                   N/A                         $ [***] per [***]
</TABLE>

<PAGE>   46

                                    EXHIBIT G

                               PENDING LIABILITIES

1. The following civil actions are pending with respect to AHP's sale of the
Product in the Territory:

                  Shimshock v. Truta, et al., Superior Court of California,
                  County of San Mateo, No. 400614<PAGE>   1
                                                                   EXHIBIT 10.14

                        CONFIDENTIAL TREATMENT REQUESTED

         Confidential Portions of This Agreement Which Have Been Redacted Are
Marked With Brackets ([***]). The Omitted Material Has Been Filed Separately
With The Securities And Exchange Commission.

                                LICENSE AGREEMENT

         THIS LICENSE AGREEMENT (the "Agreement") is entered into as of the 29th
day of January, 1999, by and between HORIZON PHARMACEUTICAL CORPORATION, a
company incorporated under the laws of Delaware, with its principal place of
business at 660 Hembree Parkway, Suite 106, Roswell, Georgia 30076 ("Horizon"),
and AMERICAN HOME PRODUCTS CORPORATION, a company incorporated under the laws of
Delaware, with its principal place of business at Five Giralda Farms, Madison,
New Jersey 07940, USA ("AHP"). Both Horizon and AHP are referred to herein
individually as a "Party" and collectively as the "Parties".

         WHEREAS, AHP has rights to certain Know-How (as hereinafter defined)
and Trademarks (as hereinafter defined) relating to the Products (as hereinafter
defined);

         WHEREAS, Horizon is qualified to market pharmaceutical products in the
Territory (as hereinafter defined);

         WHEREAS, Horizon desires to engage AHP's or its Affiliate's (as
hereinafter defined) facilities and services to manufacture (a) the Product for
distribution and sale by Horizon, and AHP is willing to enter into a separate
manufacturing and supply agreement contemporaneously herewith; and

         WHEREAS, AHP desires to grant and transfer to Horizon and Horizon
desires to receive a license and other rights and assets under the terms and
conditions set forth herein;

         NOW THEREFORE, in consideration of the foregoing premises and the
mutual promises, covenants and conditions contained in this Agreement, the
Parties agree as follows:

1.       DEFINITIONS.

         For the purposes of this Agreement, the capitalized terms hereunder
         shall have the meanings defined below:

         1.1      "AFFILIATE(S)" shall mean, in the case of either Party, any
                  corporation, joint venture, or other business entity which
                  directly or indirectly controls, is controlled by, or is under
                  common control with that Party. "Control", as used in this
                  Section 1.1, shall mean having the power to direct, or cause
                  the direction of, the

                                      -1-
<PAGE>   2

                  management and policies of an entity, whether through
                  ownership of voting securities, by contract or otherwise.
                  Notwithstanding the foregoing, for purposes of this Agreement,
                  the term "Affiliate" shall not include subsidiaries in which a
                  Party or its Affiliates owns a majority of the ordinary voting
                  power to elect a majority of the board of directors but is
                  restricted from electing such majority by contract or
                  otherwise, until such time as such restrictions are no longer
                  in effect.

         1.2      "CLOSING" shall have the meaning set forth in Section 3.3
                  hereof.

         1.3      "COMMERCIALLY REASONABLE EFFORTS" shall mean efforts and
                  resources normally used by a Party for a compound or product
                  owned by it or to which it has rights, which is of similar
                  market potential at a similar stage in its product life,
                  taking into account the competitiveness of the marketplace,
                  the proprietary position of the compound or product, the
                  regulatory structure involved, the profitability of the
                  applicable products, and other relevant factors.

         1.4      "CUSTOMER CONTRACTS" shall mean those contracts and
                  outstanding bids listed in Exhibit A hereto, between AHP or
                  its Affiliates and certain Third Parties pursuant to which
                  such Third Parties, inter alia, purchase Products from AHP or
                  such Affiliates in the Territory.

         1.5      "EFFECTIVE DATE" shall mean the date on which the Closing
                  occurs in accordance with Section 3.3 hereof.

         1.6      "FIELD" shall mean use in humans, excluding injectable forms
                  of the Substance for human use.

         1.7      "HSR ACT" means the Hart-Scott-Rodino Antitrust Improvements
                  Act of 1976, as amended, and the rules and regulations
                  promulgated thereunder.

         1.8      "KNOW-HOW" shall mean all proprietary technical and clinical
                  information, data and know-how relating to the Products,
                  whether or not patentable, owned as of the Effective Date or
                  acquired during the term of this Agreement, by AHP or its
                  Affiliates. Know-How shall include, without limitation, all
                  processes, formulas, discoveries and inventions whether
                  relating to biological, chemical, pharmacological,
                  toxicological, pharmaceutical, physical and analytical safety,
                  quality control and clinical data, including, without
                  limitation, phase IV clinical study data. Know-How shall also
                  include relevant medical information relating to the Products
                  (such as customer questions, responses thereto and adverse
                  drug event (ADE) history) in AHP's possession. The term
                  "Know-How", however, shall not include (i) any know-how,
                  processes, information and data which is, as of the Effective
                  Date or later becomes, generally available to the public or
                  (ii) any general manufacturing know-how not specific to the
                  Products.

                                      -2-
<PAGE>   3

         1.9      "LETTER OF INTENT" shall mean that certain Letter of Intent
                  which (i) is dated as of December 14, 1998 and (ii) relates to
                  the transaction contemplated by this Agreement.

         1.10     "NET SALES" shall mean amounts invoiced for sales of the
                  Products by Horizon, its Affiliates and sublicensees to Third
                  Parties in the Territory, less the sum of (i) trade, quantity
                  and cash discounts actually allowed or paid, (ii) credits or
                  allowances given or made for return of previously sold
                  products, (iii) rebates and chargebacks specifically
                  identified to the sale of the Products by Horizon, its
                  Affiliates and sublicensees, and (iv) taxes, duties or other
                  governmental charges levied on or measured by the billing
                  amount, as adjusted for rebates and refunds. Such amounts
                  shall be determined from the books and records of Horizon, its
                  Affiliates and sublicensees which shall be maintained in
                  accordance with generally accepted accounting principles.
                  Sales of Products by and between Horizon, its Affiliates and
                  sublicensees are not sales to Third Parties and shall be
                  excluded from Net Sales calculations for all purposes.

         1.11     "PRODUCT(S)" shall mean those Products listed in Exhibit B,
                  for use in the Field, each of which have been marketed by AHP
                  as of the date this Agreement was signed by the Parties.

         1.12     "PRODUCT SUPPLY AGREEMENT" shall have the meaning set forth in
                  Section 7.1 hereof.

         1.13     "REGULATORY APPROVAL" shall mean all authorizations by the
                  appropriate Regulatory Authorities which are required for the
                  manufacture (other than manufacturing facilities licenses,
                  approvals or authorizations) marketing, promotion, pricing and
                  sale of the Products in the Territory, including an approved
                  New Drug Application(s) for the Product(s) which are owned by
                  AHP or its Affiliates.

         1.14     "REGULATORY AUTHORITY" shall mean any national,
                  supra-national, regional, state or local regulatory agency,
                  department, bureau, commission, council or other governmental
                  entity in the Territory involved in the granting of Regulatory
                  Approvals for the Product including, without limitation, the
                  United States Food and Drug Administration ("FDA").

         1.15     "SUBSTANCE" shall mean the chemical substance
                  3-[(cyclopentylhydroxy phenyl acetyl) oxy] -1, 1-dimethyl
                  (pyrrolidinium bromide, otherwise known as glycopyrrolate).

         1.16     "SUPPLY PRICE" shall mean the price paid by Horizon to AHP
                  under the Product Supply Agreement for the purchase of a unit
                  of Product.

         1.17     "SYSTEMS TRANSFER PLAN" shall have the meaning set forth in
                  Section 3.2 hereof.

                                      -3-
<PAGE>   4

         1.18     "TERRITORY" shall mean the United States of America, its
                  territories and possessions, and the Commonwealth of Puerto
                  Rico.

         1.19     "THIRD PARTY(IES)" shall mean any person(s) or entity(ies)
                  other than Horizon, AHP, or their respective Affiliates.

         1.20     "TRADEMARKS" shall mean the trademarks listed on Exhibit C
                  hereto, which, as of the date this Agreement was signed by the
                  Parties, has been used by AHP in connection with the
                  promotion, marketing and sale of the Products.

         1.21     "TRANSACTION AGREEMENTS" shall mean this Agreement and the
                  Product Supply Agreement.

         1.22     "$" shall mean United States Dollars.

2.       RIGHTS GRANTED.

         2.1      LICENSES.

                  2.1.1    LICENSE OF KNOW-HOW. Subject to the terms and
                           conditions contained in this Agreement, AHP, as of
                           the Effective Date, hereby grants to Horizon an
                           exclusive license (exclusive, even as to AHP, subject
                           to the provisions of Section 2.3), under the Know-How
                           to make, have made, use, market, distribute, offer
                           for sale and sell the Product in the Territory.
                           Horizon accepts all the obligations set forth in this
                           Agreement and agrees to use the Know-How only in
                           connection with the manufacture, sale and promotion
                           of the Products in the Territory, only for so long as
                           the licenses granted under this Section 2.1.1 remain
                           in effect.

                  2.1.2    LICENSE OF TRADEMARK. Subject to the terms and
                           conditions contained in this Agreement, AHP, as of
                           the Effective Date, hereby grants to Horizon an
                           exclusive license (exclusive, even as to AHP), to use
                           the Trademark only in connection with the
                           manufacture, sale and promotion of the Products in
                           the Territory. Horizon accepts all the obligations
                           set forth in this Agreement and agrees to use the
                           Trademark in the Territory, only for so long as the
                           license granted under this Section 2.1.2 remains in
                           effect.

                  2.1.3    SUBLICENSES. Horizon may grant one or more Affiliates
                           or Third Parties sublicenses under the licenses
                           granted to Horizon under Sections 2.1.1 and 2.1.2 in
                           the Territory, provided that:

                           (a)      Horizon obtains AHP's prior written consent,
                                    such consent not to be unreasonably
                                    withheld;

                                      -4-
<PAGE>   5

                           (b)      The parties to and the economic terms of any
                                    such agreement shall be fully disclosed to
                                    AHP, and the terms of such agreement shall
                                    be consistent with all of the relevant terms
                                    and provisions of this Agreement;

                           (c)      To the extent that any such Third Party is
                                    to Perform any obligation of Horizon under
                                    this Agreement, Horizon shall remain liable
                                    for such performance; and

                           (d)      Horizon shall pay AHP the trademark
                                    royalties on all Net Sales of Product by
                                    such Affiliate or Third Party, as set forth
                                    in Section 4.2.1.

         2.2      ASSIGNMENT OF REGULATORY APPROVALS. Subject to the terms and
                  conditions contained in this Agreement, AHP shall assign to
                  Horizon at the Closing ownership of all its right, title and
                  interest in and to the Regulatory Approvals in the Territory.
                  At the Closing, all of AHP's obligations under this Agreement
                  with respect to such Regulatory Approvals shall immediately
                  terminate (with the exception of reporting, as required under
                  Section 6.2 hereof, to Horizon significant safety and efficacy
                  issues relating to Product or Substance of which AHP is aware
                  and which are required for NDA reporting in the United States)
                  and thereafter, AET shall have no further right in or to such
                  Regulatory Approvals in the Territory, except as provided in
                  Section 6.1.2 hereof Subject to the notice and cure provisions
                  of Section 11.2.2, if Horizon fails to pay to AHP the entire
                  amount of the License Fee when due, Horizon shall immediately
                  reassign the Regulatory Approvals to AHP.

         2.3      RETAINED RIGHTS. Notwithstanding the licenses granted to
                  Horizon under Section 2.1, after the Closing, AHP shall retain
                  ownership of and all rights to (i) the current NDC numbers and
                  Product Codes it uses for each of the Products (subject to
                  Horizon's right to sell Product under Section 2.7 of the
                  Product Supply Agreement), (ii) the real and personal property
                  (including, without limitation, all equipment) and general
                  manufacturing know-how used by AHP in manufacturing the
                  Products (either before, during or after the term of this
                  Agreement) other than Know-How, (iii) all accounts receivable
                  from sales of the Products by or on behalf of AHP, and (iv)
                  all inventories of the Products that have not otherwise been
                  purchased by Horizon pursuant to Section 7.1 hereof and the
                  Product Supply Agreement. Additionally, AHP retains ownership
                  of and the right to use the Know-How (i) to manufacture
                  Products for Horizon pursuant to Section 7.1 hereof and the
                  Product Supply Agreement; (ii) to manufacture Products for
                  sale outside of the Territory (including, without limitation,
                  for sale to AHP's Affiliates or Third Parties in the
                  Territory, for final distribution and sale outside of the
                  Territory); (iii) to manufacture products containing Substance
                  for use or sale, both in and outside of the Territory, as
                  veterinary pharmaceutical products and as injectable product
                  for human use; and (iv) to manufacture, use and sell Products
                  in the Territory if this Agreement is terminated by AHP
                  pursuant to Section 11.2.2 hereof and all payments due to AHP
                  pursuant to Section 4.1.1 have not been fully paid to AHP.

                                      -5-
<PAGE>   6

         2.4      HORIZON'S COVENANT NOT TO COMPETE. Horizon agrees that, during
                  the term of this Agreement, Horizon and its Affiliates will
                  not utilize the Know-How, Regulatory Approvals or Trademarks
                  in any manner to make, have made, use, market, offer to sell
                  or sell any product containing the Substance as a
                  pharmaceutically active ingredient for use as a veterinary
                  pharmaceutical agent or for injectable dosage forms for human
                  use.

3.       PRE-CLOSING ACTIVITIES; CLOSING.

         3.1      GOVERNMENT APPROVALS. Each of Horizon and AHP shall use its
                  good faith efforts to eliminate any concern on the part of any
                  court or government authority regarding the legality of the
                  proposed transaction, including, if required by state
                  antitrust authorities, promptly taking all steps to secure
                  government antitrust clearance, including, without limitation,
                  cooperating in good faith with any government investigation
                  including the prompt production of documents and information
                  demanded by a second request for documents and of witnesses if
                  requested. Horizon and AHP will cooperate and use respectively
                  all reasonable efforts to make all registrations, filings and
                  applications, to give all notices and to obtain by the Closing
                  all governmental or other consents, transfers, approvals,
                  orders, qualifications, authorizations, permits and waivers,
                  if any, and to do all other things necessary or desirable for
                  the consummation of the transactions as contemplated hereby.
                  Neither Party shall be required, however, to divest products
                  or assets or materially change its business if doing so is a
                  condition of obtaining approval under the governmental
                  approvals of the transactions contemplated by this Agreement.

         3.2      SYSTEMS TRANSFER. During the time period between the signing
                  of this Agreement by the Parties and the Closing, the Parties
                  will develop a mutually acceptable post Closing operation plan
                  substantially in the form of Exhibit D hereto (the "Systems
                  Transfer Plan") to transfer the processing of chargebacks,
                  government rebates, returns (including the processing of
                  customer credits), obligations under Customer Contracts,
                  customer service functions, and regulatory reporting functions
                  from AHP to Horizon and Know-How necessary to enable Horizon
                  to use, market, distribute and sell Product in the Territory.
                  Such plan shall be reduced to writing by Horizon and approved
                  by both Parties and shall be implemented by the Parties as
                  soon as practicable after the Closing.

         3.3      THE CLOSING.

                  3.3.1    TIME AND PLACE. The Closing of the transactions
                           contemplated hereby shall take place at 10:00 A.M.
                           (local time) on January 29, 1999 at the offices of
                           Wyeth-Ayerst Laboratories Division of American Home
                           Products Corporation, St Davids, Pennsylvania, or at
                           such other time and place as the Parties may agree.
                           The Closing shall be effective as of midnight on the
                           Effective Date.

                                      -6-
<PAGE>   7

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                  3.3.2    PAYMENT OF LICENSE FEE. At the Closing, Horizon shall
                           make the payment required by Section 4.1(i) hereof,
                           which payment shall be made by wire transfer in funds
                           immediately available to such bank account as AHP may
                           designate at least three (3) business days in
                           advance.

                  3.3.3    CUSTOMER INFORMATION. To the extent the following
                           items have not previously been provided to Horizon,
                           AHP, at the Closing, will deliver to Horizon

                           (a)      complete and accurate copies of AHP's
                                    relevant customer lists including relevant
                                    sales data for the Products; and

                           (b)      copies of current and pending customer sales
                                    contracts for the Product, which contracts
                                    shall be redacted for purposes of deleting
                                    information that is not related to the
                                    Product and other confidential information.

                  3.3.4    OTHER AGREEMENTS. At the Closing, Horizon and AHP
                           shall each execute and deliver to the other the
                           Systems Transfer Plan and the Product Supply
                           Agreement in the form attached hereto as Exhibit F.

                  3.3.5    CERTIFICATIONS OF REPRESENTATIONS AND WARRANTIES. At
                           the Closing, each Party shall certify to the other
                           that the representations and warranties set forth in
                           Article 10 hereof remain true and in effect as of the
                           day of Closing. In the event that one or more of the
                           representations and warranties do not remain true and
                           in effect as of the day of Closing, the Party
                           receiving such certification shall have the option to
                           (i) complete the Closing (and such Party shall be
                           required to expressly waive its rights under the
                           specific representation and warranty which is no
                           longer true and/or in effect as of the day of
                           closing) or (ii) terminate this Agreement as provided
                           in Section 11.2.1.

         3.4      CONDUCT OF BUSINESS FROM SIGNING TO CLOSING. AHP covenants and
                  agrees that, during the period between the signing of this
                  Agreement and Closing, it will use its Commercially Reasonable
                  Efforts to conduct the business relating to Product in a
                  manner consistent with its prior practices.

4.       CONSIDERATION.

         4.1      LICENSE FEE. In partial consideration of the licenses granted
                  to Horizon under Section 2.1 hereof and the other rights and
                  assets transferred to Horizon hereunder, Horizon shall pay AHP
                  a nonrefundable, noncreditable license fee (the "License Fee")
                  as follows (i) four million dollars ($4,000,000) which shall
                  be due and payable at the Closing and (ii) eight calendar
                  quarter payments each in the

                                      -7-
<PAGE>   8
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                  amount of two hundred twenty five thousand dollars ($225,000)
                  due May 1, 1999; August 1, 1999; November 1, 1999; February 1,
                  2000; May 1, 2000; August 1, 2000; November 1, 2000; and
                  February 1, 2001, for a total of one million eight hundred
                  thousand dollars ($1,800,000) in addition to the payment due
                  under Section 4.1(i) above.

         4.2      ROYALTIES.

                  4.2.1    ROYALTY RATES. In further consideration of the
                           trademark license granted to Horizon under Section
                           2.1.2 hereof, during the term of this Agreement,
                           Horizon shall pay AHP royalties in the amount of

                           (a)      [***] of the Net Sales for all Products sold
                                    by or on behalf of Horizon, its Affiliates
                                    and sublicensees prior to the [***]
                                    anniversary of the Effective Date up to
                                    annual Net Sales of $[***]; and

                           (b)      [***] of the Net Sales for all Products sold
                                    by or on behalf of Horizon, its Affiliates
                                    and sublicensees prior to the [***]
                                    anniversary of the Effective Date of Net
                                    Sales above annual Net Sales of $[***]; and

                           (c)      [***] of the Net Sales for all Products sold
                                    by or on behalf of Horizon, its Affiliates
                                    and sublicensees after the [***] anniversary
                                    of the Effective Date.

                  4.2.2    MINIMUM ROYALTIES. During the period from the
                           Effective Date to the fifth anniversary of the
                           Effective Date, Horizon shall pay a minimum royalty
                           to AHP each calendar quarter of [***] dollars
                           ($[***]).

                  4.2.3    SCOPE OF ROYALTY OBLIGATIONS. No royalties shall be
                           due upon the sale or other transfer among Horizon and
                           its Affiliates, but in such cases the royalty shall
                           be due and calculated upon Horizon's or its
                           Affiliates' Net Sales to the first independent Third
                           Party.

                  4.2.4    ROYALTIES PAID QUARTERLY. For each calendar quarter,
                           or part thereof, in which Horizon sells Product and
                           is obligated to pay to AHP royalties with respect to
                           such sales pursuant to this Section 4.2, Horizon
                           shall, for the first four calendar quarters following
                           the Effective Date within forty five (45) calendar
                           days, and for each calendar quarter thereafter within
                           thirty (30) calendar days, following the close of
                           each such calendar quarter furnish to AHP a written
                           report for the calendar quarter showing (i) the
                           number of units of each Product (by NDC number) sold
                           by Horizon, its  Affiliates and sublicensees in the
                           Territory during such calendar quarter, (ii) the Net
                           Sales of Product (by NDC number) sold by Horizon, its

                                      -8-
<PAGE>   9

                           Affiliates and sublicensees in the Territory during
                           such calendar month, and (iii) the royalties payable
                           under this Agreement for such calendar quarter.
                           Simultaneously with the submission of the written
                           report, Horizon shall pay to AHP a sum equal to the
                           aggregate royalty due for such calendar quarter
                           calculated in accordance with this Agreement
                           (reconciled for any previous overpayments,
                           underpayments or credits).

         4.3      METHOD OF PAYMENT. All payments to be made by Horizon to AHP
                  pursuant to Section 4.2 hereof shall be made in United States
                  dollars by wire transfer simultaneously with the submission of
                  the report required under Section 4.2.4 hereof.

         4.4      MAINTENANCE OF RECORDS BY HORIZON; AUDITS.

                  4.4.1    RECORD KEEPING BY HORIZON. Horizon and its Affiliates
                           shall, and shall cause its sublicensees to, keep
                           accurate books and accounts of record in connection
                           with the sale by or on behalf of Horizon, its
                           Affiliates and sublicensees of the Products in
                           sufficient detail (i) to permit accurate
                           determination of all figures necessary for
                           verification of payments required to be paid
                           hereunder and (ii) to verify compliance with the
                           provisions of Section 8.3 hereof. Horizon, its
                           Affiliates and sublicensees shall maintain such
                           records for a period of three (3) years after the end
                           of the year in which they were generated.

                  4.4.2    AUDIT BY AHP. AHP, through an independent certified
                           public accountant reasonably acceptable to Horizon,
                           shall have the right, at its own expense, to access
                           the books and records of Horizon, its Affiliates and
                           sublicensees as may be reasonably necessary (i) to
                           verify the accuracy of the royalty reports and all
                           payments made hereunder and (ii) to verify compliance
                           with the provisions of Section 8.3 hereof, including,
                           without limitation, the determination of any
                           additional payments that may be due to AHP pursuant
                           to Section 8.3 hereof. Such access shall be conducted
                           after reasonable prior written notice to Horizon and
                           during ordinary business hours and shall not be more
                           frequent than once per calendar year, in respect of
                           any calendar year ending not more than thirty (30)
                           months prior to the date of such notice. Upon the
                           expiration of the thirty (30) month period described
                           in the immediately preceding sentence, the
                           calculation of amounts payable with respect to such
                           time periods shall be binding and conclusive upon
                           AHP, and Horizon, its Affiliates and sublicensees
                           shall be released from any liability or
                           accountability with respect to payments for such time
                           periods. The parties agree that such independent
                           certified public accountant shall disclose to AHP
                           only whether the royalty reports are correct or
                           incorrect, the specific details concerning any
                           discrepancies in such reports, whether the provisions
                           of Section 8.3 hereof have been complied with and the
                           specific details concerning any noncompliance with

                                      -9-
<PAGE>   10

                           the provisions of Section 8.3 hereof. AHP agrees to
                           keep in strict confidence all information learned in
                           the course of such audit, except when it is necessary
                           to reveal such information in order to enforce its
                           rights under this Agreement.

                  4.4.3    UNDERPAYMENTS/OVERPAYMENTS. If such independent
                           certified public accountant's report shows any
                           underpayment, Horizon shall remit or shall cause its
                           Affiliates and sublicensees to remit to AHP within
                           thirty (30) days after AHP's receipt of such report,
                           (i) the amount of such underpayment (ii) interest on
                           such underpayment at the prime rate quoted by Chase
                           Manhattan Bank N.A. from the date payment was first
                           due until the date of payment of such underpayment
                           and (iii) if such underpayment exceeds five percent
                           (5%) of the total amount owed for the calendar year
                           then being audited, the reasonable fees and expenses
                           of such independent certified public accountant
                           performing the audit. Any overpayments, less the
                           reasonable fees and expenses of such independent
                           certified public accountant, shall be fully
                           creditable against amounts payable in subsequent
                           payment periods.

         4.5      TAXES AND WITHHOLDING. All taxes levied or incurred on account
                  of any payments from Horizon to AHP accruing under this
                  Agreement, by national, state or local governments, will be
                  assumed and paid by Horizon, except taxes levied thereon as
                  income to AHP and if such taxes are required to be withheld by
                  Horizon they will be deducted from payments due to AHP and
                  will be timely paid by Horizon to the proper taxing authority
                  for the account of AHP, a receipt or other proof of payment
                  therefor secured and sent to AHP as soon as practicable.

5.       DISCLOSURE OF KNOW-HOW; ASSUMPTION OF OBLIGATIONS

         5.1      DISCLOSURE OF KNOW-HOW. At or immediately after the Closing,
                  in accordance with Section 3.2, AHP shall promptly disclose to
                  Horizon that Know-How currently utilized by or on behalf of
                  AHP or its Affiliates which is necessary to enable Horizon to
                  use, market, distribute and sell the Product in accordance
                  with the Transaction Agreements.

         5.2      CUSTOMER CONTRACTS. A complete and accurate list of each of
                  the current and pending Customer Contracts pursuant to which
                  AHP or an AHP Affiliate is, with respect to the current
                  Customer Contracts immediately prior to the date of this
                  Agreement, selling Products, along with other products of AHP
                  and its Affiliates, to Third Party buyers is attached hereto
                  as Exhibit A. AHP agrees that between the date of signing of
                  this Agreement and Closing, no new Customer Contracts shall be
                  executed without first consulting with Horizon. AHP further
                  agrees that between the date of signing of this Agreement and
                  Closing, no new bids shall be made without first consulting
                  with and obtaining the written consent of Horizon. The parties
                  agree that bids outstanding as of the date of the signing of
                  this

                                      -10-
<PAGE>   11

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                           Agreement shall be handled in AHP's normal course of
                           business. The Parties understand and agree that
                           because the right to sell Product is being
                           transferred to Horizon pursuant to this Agreement, as
                           of the Effective Date AHP will no longer have the
                           right to sell or, except as provided below, adjust
                           the price of Product under the Customer Contracts,
                           provided, however, that Horizon agrees that it will
                           continue to honor all of AHP's commitments made in
                           each such Customer Contract with respect to supplying
                           the Product, including, without limitation, the sale
                           prices as adjusted in accordance with such Customer
                           Contracts, for the Products throughout the term of
                           each such Customer Contract. After the Closing, upon
                           Horizon's request, AHP and Horizon will request each
                           Third Party to the Customer Contracts to relieve AHP
                           of its obligations to provide Product under each such
                           Customer Contract. In addition, to the extent that
                           AHP and Horizon are unable to obtain a release from a
                           Third Party of AHP's obligations to supply the
                           Product under such Customer Contract, then upon the
                           request of Horizon, AHP shall use its Commercially
                           Reasonable Efforts to take actions that are permitted
                           under the terms of such Customer Contract to minimize
                           the commitment for Product thereunder, including
                           without limitation, adjusting Product prices,
                           reducing the term of such Customer Contract solely
                           with respect to the Product and terminating AHP's
                           obligations with respect to Product under any such
                           Customer Contract, provided, however, that AHP shall
                           not be required to either (i) adjust prices or terms
                           relating to products other than Products, (ii) make
                           any payments to such Third Party in consideration for
                           making such price adjustments or modifications to the
                           Customer Contract or (iii) terminate any such
                           Customer Contract with respect to products other than
                           Products. AHP agrees that following the signing of
                           this Agreement, it will not take any action with
                           respect to any Customer Contract which will extend
                           the term of such Customer Contract for any Product or
                           otherwise adversely affect Horizon with respect to
                           any Product, without the prior written consent of
                           Horizon. All sales of the Product after the Closing
                           shall be booked by Horizon.

         5.3      CHARGEBACKS. As of the Closing, Horizon will be responsible
                  for all customer chargebacks for Product sold in the
                  Territory, provided, however, that, with respect to such
                  Product sales, AHP, for a period of [***] after the Effective
                  Date, will reimburse Horizon for all qualified customer
                  chargebacks having Activity Dates prior to the Effective Date.
                  For purposes of this Section 5.3, the "Activity Date" is the
                  date a wholesaler ships the Product to a customer under terms
                  of a customer sales contract or pursuant to a purchase order
                  issued by such customer.

         5.4      REBATES. As of the Closing, Horizon will be fully responsible
                  for all Federal, State and Third Party rebate programs for
                  Product sold in the Territory under Horizon's NDC numbers,
                  including all reporting activities associated with such
                  programs. Additionally, as of the Closing, Horizon will be
                  financially responsible for all Federal, State and Third Party
                  rebate programs for Product sold in the Territory under AHP's
                  label, provided, however, that with respect to such Product
                  sales, AHP will continue to prepare the appropriate Federal
                  and State rebate

                                      -11-
<PAGE>   12

                  reports and process Federal and State rebates for the sale of
                  such Product and Horizon will reimburse AHP for (i) 50% of all
                  such rebates paid which have a Report Date after the Closing
                  and on or before March 31, 1999 and (ii) one hundred percent
                  (100%) of all such rebates paid which have a Report Date after
                  March 31, 1999. For purposes of this Section 5.4, the "Report
                  Date" is the date a qualified rebate invoice is issued under
                  applicable Federal or State Rebate Programs.

         5.5      RETURNS. As of the Effective Date, Horizon will be responsible
                  for all returns of Product sold in the Territory, provided,
                  however, that AHP will reimburse Horizon for all qualified
                  returns of such Product sold by AHP to Third Parties prior to
                  the Effective Date. The Parties agree to track sales and
                  returns of Product by lot number to determine whether such
                  Product was sold to Third Parties by AHP prior to the
                  Effective Date or by Horizon after the Effective Date. AHP's
                  liability pursuant to this Section 5.5 for such returns shall
                  not exceed twenty five thousand dollars ($25,000.00) and all
                  returns in excess of such limitation shall be borne solely by
                  Horizon.

         5.6      REIMBURSEMENT. AHP shall reimburse Horizon for chargebacks,
                  rebates and returns according to Sections 5.3, 5.4 and 5.5 as
                  follows: Horizon agrees to provide AHP with an invoice for
                  amounts due under Sections 5.3, 5.4 and 5.5 within thirty (30)
                  days after the end of each calendar month with the
                  documentation required to verify the same. AHP agrees to
                  reimburse Horizon in accordance with Sections 5.3, 5.4 and 5.5
                  hereof within thirty (30) days after the receipt of the
                  invoice and all required documentation.

6.       REGULATORY MATTERS.

         6.1      HORIZON RESPONSIBILITIES.

                  6.1.1    DISCLOSURE OF REGULATORY APPROVALS. Within thirty
                           (30) days after the Effective Date, AHP shall provide
                           Horizon with a copy of all correspondence or other
                           documents reasonably related to such Regulatory
                           Approvals. Additionally, within such thirty (30) day
                           period, AHP shall provide to Horizon a current list
                           of suppliers for Materials used in the manufacture of
                           Products.

                  6.1.2    RIGHT OF REFERENCE. Horizon irrevocably grants to AHP
                           the right to reference the Regulatory Approvals to
                           support AHP's Product related activities outside of
                           the Territory and to support any veterinary
                           pharmaceutical products containing Substance or any
                           injectable products for human use, which AHP
                           currently markets or sells or may, in the future,
                           market or sell. Horizon shall not amend the
                           Regulatory Approvals without the prior written
                           consent of AHP, such consent not to be unreasonably
                           withheld, and AHP shall respond to Horizon's request
                           for consent within thirty (30) days from such
                           request.

                                      -12-
<PAGE>   13

                  6.1.3    RESPONSIBILITIES. After the Effective Date, Horizon
                           shall be solely responsible for conducting all
                           activities in connection with such Regulatory
                           Approvals, including, without limitation,
                           communicating and preparing and filing all reports
                           (including, without limitation, adverse drug
                           experience reports) with the appropriate Regulatory
                           Authorities in the Territory and interacting with any
                           Third Parties with respect to Products sold or
                           distributed in the Territory; provided, however, that
                           for up to sixty (60) days after the Effective Date,
                           AHP shall assist and cooperate in the transition of
                           such activities to Horizon. Additionally, to the
                           extent that Horizon is obligated, under applicable
                           laws and regulations, to report to the Regulatory
                           Authorities in the Territory, adverse drug
                           experiences associated with Product sold by or on
                           behalf of AHP outside of the Territory, AHP shall
                           provide Horizon with information about such adverse
                           drug experiences in accordance with the provisions of
                           Section 6.2 hereof and to the extent that, AHP is
                           obligated under applicable laws and regulations to
                           report adverse drug experiences associated with
                           Product sold by or on behalf of Horizon inside the
                           Territory, Horizon shall provide AHP with information
                           about such adverse drug experiences in accordance
                           with the provisions of Section 6.2 hereof. Upon
                           written request of Horizon, AHP shall provide Horizon
                           with all additional written information in AHP's
                           possession which directly relates to the Products in
                           the Field as AHP shall have developed and which would
                           be useful in supporting the Regulatory Approvals.

                  6.1.4    PAYMENT OF FEES. After the Effective Date, Horizon
                           shall pay all NDA maintenance fees and any
                           establishment license fees of Horizon, its Affiliates
                           or Third Parties which must be paid with respect to
                           facilities used in the manufacture of Product by or
                           on behalf of Horizon. Notwithstanding the foregoing,
                           for so long as AHP is supplying Product to Horizon in
                           accordance with the Product Supply Agreement, AHP
                           shall pay any establishment license fees which must
                           be paid with respect to AHP's, its Affiliate's or
                           subcontractor's facilities used for the manufacture
                           of such Product.

         6.2      ADVERSE DRUG EXPERIENCE REPORTING. In order for the Parties to
                  comply with their respective responsibilities under this
                  Article 6 and otherwise relating to the reporting of adverse
                  drug experiences, to the extent either Party receives any
                  information regarding adverse drug experiences related to the
                  use of the Product, whether such use is within or outside of
                  the Territory, such Party shall promptly provide the other
                  Party with such information in accordance with the Adverse
                  Event Reporting Procedures (as may be amended from time to
                  time upon mutual agreement) set forth in Exhibit E.

                                      -13-
<PAGE>   14
                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

7.       SUPPLY.

         7.1      SUPPLY OF PRODUCT BY AHP. For the term set forth in the
                  Product Supply Agreement, AHP, either directly or through one
                  or more subcontractors, shall manufacture and supply Products
                  to Horizon for sale in the Territory and Horizon shall
                  purchase from AHP its entire requirements of Products for sale
                  in the Territory, all in accordance with the terms and
                  conditions of the Product Supply Agreement, in the form
                  attached hereto as Exhibit F, to be entered into by the
                  Parties at the Closing.

         7.2      SUPPLY OF PRODUCT BY HORIZON. Following the term set forth in
                  the Product Supply Agreement and thereafter:

                  (a)      Horizon shall be responsible, at its own expense, for
                           manufacturing its requirements of Product, either by
                           itself or through a Third Party;

                  (b)      Upon AHP's request, Horizon shall purchase from AHP
                           (i) reasonable quantities of AHP's residual
                           inventories of Products having not less than twelve
                           months remaining dating at the then current purchase
                           price and (ii) reasonable quantities of AHP's
                           useable, residual inventories of Product specific
                           Materials (as defined in the Product Supply
                           Agreement), including, without limitation, all labels
                           and other Product specific packaging materials at
                           AHP's fully-absorbed manufacturing costs;

                  (c)      Upon AHP's request, Horizon would supply AHP's
                           requirements of Products for sale by AHPC outside the
                           Territory at Horizon's then fully-absorbed
                           manufacturing cost plus a [***] mark-up, which
                           purchase prices shall be increased once each year by
                           [***].

                  (d)      Upon AHP's request, Horizon will use its Commercially
                           Reasonable Efforts to facilitate discussions between
                           AHP and any Third Party manufacturer with which
                           Horizon may be in discussions regarding the
                           manufacture of the Product following the term of the
                           Product Supply Agreement.

                                      -14-
<PAGE>   15
         7.3      SUPPLY OF SUBSTANCE BY HORIZON. Following the term set forth
                  in the Product Supply Agreement, and thereafter:

                  (a)       Horizon shall be responsible, at its own expense,
                            for manufacturing its requirements of bulk
                            Substance, either by itself or through a Third
                            Party;

                  (b)      Upon AHP's request, Horizon shall purchase from AHP
                           (i) reasonable quantities of AHP's residual
                           inventories of the bulk Substance and (ii) reasonable
                           quantities of AHP's residual inventories of Substance
                           specific Materials (as defined in the Substance
                           Supply Agreement), including without limitation, all
                           labels and other Substance specific packaging
                           materials, in each case at AHP's fully-absorbed
                           manufacturing costs; and

                  (c)      Upon AHP's request, Horizon will use its Commercially
                           Reasonable Efforts to facilitate discussions between
                           AHP and any Third Party manufacturer with which
                           Horizon may be in discussions regarding the
                           manufacture of the Substance following the term of
                           the Product Supply Agreement.

8.       PROMOTION, MARKETING AND SALE OF PRODUCTS.

         8.1      DILIGENCE. As of the Closing, Horizon shall be solely
                  responsible for and shall use its Commercially Reasonable
                  Efforts to promote, market, sell and distribute the Products
                  in the Territory.

         8.2      MATERIALS AND PROMOTIONAL CLAIMS. Horizon at all times shall
                  be solely responsible for complying with all applicable laws
                  and regulations in its promotion and marketing of the
                  Products.

         8.3      TIMING OF SALES. Horizon agrees that it and its Affiliates
                  shall not, by any action or act of omission cause sales of
                  Products that would have otherwise occurred prior to the end
                  of the fifth anniversary of the Effective Date, to occur after
                  the fifth anniversary of the Effective Date.

                  Such actions or acts of omission may include, without
                  limitation, announcing or implementing changes in the price of
                  Products, or delaying the filling of orders. AHP shall have
                  the right to audit, in accordance with Section 4.5.2 hereof
                  all of Horizon's records reasonably necessary to verify
                  compliance with this Section and if AHP determines that either
                  Horizon or its Affiliates has taken any such actions or
                  committed any such act of omission then, for purposes of the
                  payment of royalties under Section 4.2 hereof, the Net Sales
                  of Product made during the three months after the fifth
                  anniversary of the Effective Date shall be treated as if such
                  sales occurred prior to the fifth anniversary of the Effective
                  Date.

                                      -15-
<PAGE>   16
9.       TRADEMARKS.

         9.1      USE OF TRADEMARKS. Horizon agrees to use the Trademarks only
                  in connection with the Products and in the manner and style
                  which shall have the prior written approval of AHP. Horizon
                  shall submit to AHP samples of all commercial materials
                  containing any of the Trademarks. AHP, within thirty (30) days
                  of its receipt of such materials, shall have the right to
                  reasonably comment on the usage of the Trademarks in such
                  materials and Horizon, at its own cost and expense, will
                  promptly correct any improper usage of the Trademarks. Horizon
                  agrees not to claim or to assert any right of ownership in or
                  to such Trademarks or the goodwill associated therewith and
                  shall take no action which may destroy, damage or impair in
                  any way the ownership or rights of AHP in and to such
                  Trademarks. Horizon shall not register anywhere in the world
                  in its own name, or on behalf of any other person or entity,
                  any trademark, trade dress, brands, labeling, designs or other
                  indicia of ownership identical to, or confusingly similar to,
                  the Trademarks, and shall not associate the Trademarks with
                  any articles other than the Products and shall, at the request
                  of AHP, do all such acts and things and execute all such
                  documents as AHP shall in its reasonable discretion consider
                  necessary or proper to register or maintain the registration
                  of the Trademarks in any country of the Territory. Should
                  usage of the Trademarks in any country vest title thereto in
                  Horizon, then Horizon shall at AHP's request, immediately
                  assign and transfer such title to AHP.

         9.2      QUALITY CONTROL. Horizon will not permit the quality of
                  Products to deteriorate while in its possession so as to
                  adversely affect the goodwill associated with the Trademarks.
                  Horizon shall upon request of AHP, from time to time furnish
                  AHP, without charge, specifications and samples of Products
                  for quality review by AHP. AHP or an authorized representative
                  thereof shall have the right, at all reasonable times, to
                  inspect the finished goods in relation to which the Trademarks
                  are to be used, as part of appropriate quality control.

         9.3      INFRINGEMENT OF TRADEMARKS. In the event that, either Horizon
                  or AHP learn that any of the Trademarks pertaining to Products
                  is being infringed in the Territory by any Third Party, it
                  shall promptly notify the other Party of such infringement.
                  AHP shall have the right, but not the obligation, to act to
                  terminate any such Third Party infringement, including,
                  without limitation, prosecuting a lawsuit or other legal
                  proceeding, at AHP's own expense. In the event that AHP takes
                  any such action to terminate such infringement, Horizon may,
                  at its sole option, take appropriate steps to join AHP in such
                  action and share equally in the costs thereof. If and only if
                  Horizon joins such action as stated in the preceding sentence,
                  AHP and Horizon shall share equally in any recovery which may
                  be received as a result of such action less the reimbursement
                  of each Party for the out-of-pocket expenses incurred in
                  taking, joining and prosecuting such action. Notwithstanding
                  the foregoing, Horizon shall fully cooperate with AHP in any
                  action AHP takes to terminate such infringement and, to the
                  extent AHP recovers

                                      -16-
<PAGE>   17

                  damages from such Third Party, through settlement or
                  otherwise, shall be reimbursed by AHP for all reasonable
                  expenses incurred in connection therewith. If AHP fails to
                  take any action within sixty (60) days after Horizon's
                  request, Horizon shall have the right to act as it sees fit to
                  terminate the infringement, including without limitation,
                  prosecuting a lawsuit or other legal proceeding, at Horizon's
                  own expense. Horizon may deduct its costs and expenses for
                  such action from trademark royalties accruing under Section
                  4.2 after the date of filing of such action. In the event that
                  Horizon takes any such action to terminate such infringement,
                  AHP may, at its sole option, take appropriate steps to join
                  Horizon in such action and share equally in the costs thereof.
                  If and only if AHP joins such action as stated in the
                  preceding sentence, AHP and Horizon shall share equally in any
                  recovery which may be received as a result of such action less
                  the reimbursement of each Party for the out-of-pocket expenses
                  incurred in taking, joining and prosecuting such action.
                  Notwithstanding the foregoing, AHP shall fully cooperate with
                  Horizon in any action Horizon takes to terminate such
                  infringement, including without limitation, agreeing to be
                  joined as party plaintiff and approving any reasonable
                  settlement agreement achieved by Horizon, and to the extent
                  Horizon receives damages from such Third Party, through
                  settlement or otherwise, shall be reimbursed by Horizon for
                  all reasonable expenses incurred in connection therewith and
                  deductions from trademark royalties pursuant to this Section
                  9.3.

10.      REPRESENTATIONS AND WARRANTIES.

         10.1     REPRESENTATIONS AND WARRANTIES OF EACH PARTY. As of the
                  signing of this Agreement, each of Horizon and AHP hereby
                  represents, warrants and covenants to the other Party hereto
                  as follows:

                  (a)      it is a corporation or entity duly organized and
                           validly existing under the laws of the state or other
                           jurisdiction of incorporation or formation;
                  (b)      the execution, delivery and performance of this
                           Agreement by such Party has been duly authorized by
                           all requisite corporate action and do not require any
                           shareholder action or approval;
                  (c)      it has the power and authority to execute and deliver
                           this Agreement and to perform its obligations
                           hereunder;
                  (d)      the execution, delivery and performance by such Party
                           of this Agreement and its compliance with the terms
                           and provisions hereof does not and will not conflict
                           with or result in a breach of any of the terms and
                           provisions of or constitute a default under (i) a
                           loan agreement, guaranty, financing agreement,
                           agreement affecting a product or other agreement or
                           instrument binding or affecting it or its property;
                           (ii) the provisions of its charter or operative
                           documents or bylaws; or (iii) any order, writ,
                           injunction or decree of any court or governmental
                           authority entered against it or by which any of its
                           property is bound; and

                                      -17-
<PAGE>   18

                  (e)      it shall at all times comply with all applicable
                           material laws and regulations relating to its
                           activities under this Agreement.

         10.2     REPRESENTATIONS AND WARRANTIES OF AHP. As of the signing of
                  this Agreement, AHP hereby represents and warrants to Horizon
                  as follows:

                  (a)      Except as listed in Exhibit G, there are no (i)
                           pending or, to AHP's knowledge, threatened product
                           liability, breach of warranty or other claims,
                           actions, arbitrations, administrative or other
                           proceedings regarding the Product or the Trademarks,
                           to which AHP is a party in the Territory; or (ii)
                           pending or, to AHP's knowledge, overtly threatened
                           claim against AHP asserting that any of the Know-How
                           infringes or violates the rights of Third Parties.

                  (b)      AHP is the sole owner of the Trademarks, the Know-How
                           and the Regulatory Approvals for the Product in the
                           Territory and AHP has not sublicensed, pledged,
                           encumbered, assigned, transferred or granted any
                           rights or interest therein to any Third Party
                           inconsistent with the rights granted to Horizon under
                           the Transaction Agreements, and prior to the Closing,
                           AHP will enter into no such agreement with any
                           Affiliate or Third Party.

                  (c)      AHP has furnished Horizon with access to a complete
                           copy of the Regulatory Approvals, including all
                           material amendments and supplements thereto. To the
                           best of AHP's knowledge, the Regulatory Approvals are
                           in good standing and nothing has come to the
                           attention of AHP which has, or reasonably should
                           have, led AHP to believe that the Regulatory
                           Approvals are not in good standing. To the best of
                           AHP's knowledge, there is no pending or overtly
                           threatened action by the FDA which will have a
                           material adverse effect on the Regulatory Approvals.

                  (d)      AHP represents and warrants that the list of Customer
                           Contracts provided herein is accurate and complete
                           with respect to current Customer Contracts and is, to
                           the best of AHP's knowledge, accurate and complete
                           with respect to pending Customer Contracts.

                  (e)      AHP has not given any notice to any Third Parties
                           asserting misappropriation of trade secrets relating
                           to the Know-How.

                  (f)      EXCEPT AS OTHERWISE EXPRESSLY PROVIDED IN THIS
                           AGREEMENT OR IN THE PRODUCT SUPPLY AGREEMENT, AHP
                           MAKES NO OTHER REPRESENTATIONS OR WARRANTIES, EITHER
                           EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION,
                           WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
                           PARTICULAR PURPOSE, WITH RESPECT TO THE PRODUCTS OR
                           THE TRADEMARKS OR HORIZON'S USE THEREOF.

                                      -18-
<PAGE>   19

         10.3     REPRESENTATIONS AND WARRANTIES OF HORIZON. As of the signing
                  of this Agreement, Horizon represents and warrants to AHP that
                  it has properly determined that the net present value of the
                  transactions contemplated by this Agreement is less than
                  fifteen million dollars ($15,000,000) and no HSR filing is
                  required in connection with the transactions contemplated
                  hereby.

         10.4     REPRESENTATION BY LEGAL COUNSEL. Each Party hereto represents
                  that it has been represented by legal counsel in connection
                  with this Agreement and acknowledges that it has participated
                  in the drafting hereof. In interpreting and applying the terms
                  and provisions of this Agreement, the Parties agree that no
                  presumption shall exist or be implied against the Party which
                  drafted such terms and provisions.

11.      TERM AND TERMINATION.

         11.1     TERM. This Agreement shall be effective as of the Effective
                  Date and, unless terminated earlier by mutual written
                  agreement of the Parties or pursuant to this Article 11, shall
                  remain in full force and effect for so long as Horizon sells
                  Product in the Territory (the "Term"). Notwithstanding the
                  foregoing, upon the payment of all amounts due pursuant to
                  Section 4.1 hereof the Know-How license granted to Horizon
                  pursuant to Section 2.1.1 hereof shall become a fully paid-up,
                  perpetual exclusive (exclusive except as to veterinary
                  pharmaceutical products and injectable human uses by AHP and
                  its Affiliates neither of which shall have the right to
                  sublicense) license.

         11.2     TERMINATION.

                  11.2.1   CERTIFICATIONS OF REPRESENTATION AND WARRANTIES.
                           Either Party may terminate this Agreement if, in
                           accordance with Section 3.3.5 hereof, the other Party
                           certifies that one or more of its representations and
                           warranties set forth in Article 10 hereof do not
                           remain true and in effect as of the day of Closing.

                  11.2.2   TERMINATION FOR CAUSE BOTH PARTIES. This Agreement
                           may be terminated by written notice by either Party
                           (subject to the provisions of Section 11.2.3) at any
                           time during the Term of this Agreement:
                           (a)      for material breach by the other Party,
                                    which breach remains uncured for thirty (30)
                                    days in the case of nonpayment of any amount
                                    due and ninety (90) days for all other
                                    breaches, each measured from the date
                                    written notice of such breach is given to
                                    the breaching Party, or, if such breach is
                                    not susceptible of cure within such ninety
                                    (90) day period and the breaching Party uses
                                    diligent good faith efforts to cure such
                                    breach, for one hundred eighty (180) days
                                    after written notice to the breaching Party;
                                    or

                                      -19-
<PAGE>   20

                           (b)      upon the filing or institution of
                                    bankruptcy, reorganization, liquidation or
                                    receivership proceedings, or upon an
                                    assignment of a substantial portion of the
                                    assets for the benefit of creditors by the
                                    other Party, or in the event a receiver or
                                    custodian is appointed for such Party's
                                    business, or if a substantial portion of
                                    such Party's business is subject to
                                    attachment or similar process; provided,
                                    however, that in the case of any involuntary
                                    bankruptcy proceeding such right to
                                    terminate shall only become effective if the
                                    proceeding is not dismissed within ninety
                                    (90) days after the filing thereof.

                  11.2.3   EFFECT OF TERMINATION FOR CAUSE ON LICENSE.

                           (a)      In the event that Horizon breaches this
                                    Agreement pursuant to Section 11.2.2 then it
                                    shall be AHP's sole option:

                                    (i)     to terminate this Agreement, in
                                            which case all rights to the
                                            Know-How, the Regulatory Approvals
                                            and the Trademarks shall revert to
                                            AHP (unless all payments under
                                            Section 4.1 have been fully paid to
                                            AHP) and Horizon shall remain
                                            obligated to make all payments under
                                            Sections 4.1 and 4.2 which have
                                            accrued as of the date of
                                            termination; or

                                    (ii)    to accelerate the payments required
                                            under Section 4.1 so that they shall
                                            become immediately due and payable,
                                            in which case this Agreement shall
                                            remain in full force and effect, and
                                            Horizon shall remain obligated to
                                            make all payments required under
                                            Sections 4.1 and 4.2; or

                                    (iii)   to pursue all legal and equitable
                                            remedies available to it, in which
                                            case the Agreement shall remain in
                                            full force and effect and Horizon
                                            shall remain obligated to make all
                                            payments required under Sections 4.1
                                            and 4.2.

                           (b)      In the event that AHP breaches this
                                    Agreement pursuant to Section 11.2.2 then it
                                    shall be Horizon's sole option:
                                    (i)      to terminate this Agreement, in
                                             which case all rights to the
                                             Know-How and the Regulatory
                                             Approvals shall be vested in
                                             Horizon (if all payments under
                                             Section 4.1 have been fully paid to
                                             AHP) and the license under the
                                             Trademarks shall be deemed to be
                                             fully paid-up and Horizon shall
                                             remain obligated to make only those
                                             payments under Section 4.2 which
                                             have accrued as of the date of
                                             termination; or

                                      -20-
<PAGE>   21

                                    (ii)    to pursue all legal and equitable
                                            remedies available to it, in which
                                            case the Agreement shall remain in
                                            full force and effect and Horizon
                                            shall remain obligated to make all
                                            payments required under Sections 4.1
                                            and 4.2.

         11.3     SURVIVAL. The provisions of Articles 1, 2, 6, 12 and 13 and
                  Sections 4.4, 4.5, 11.2.3, 14.2.3, 14.6, 14.7, 14.8, 14.9, and
                  14.10 shall survive expiration or any earlier termination of
                  this Agreement. Any payments that become due and payable prior
                  to expiration, which have not been paid, shall survive
                  expiration or any earlier termination of this Agreement.

12.      INDEMNIFICATION.

         12.1     NOTICE AND ASSISTANCE. Each Party shall promptly notify the
                  other, in writing, if it learns of any litigation, claim,
                  administrative or criminal proceedings (collectively
                  "Actions"), related to the Product, the Substance, the
                  Trademark, or any Regulatory Approval, asserted or threatened
                  against such Party (the "Defending Party"). With respect to
                  any Actions relating to the Product, the Substance, the
                  Trademark or any Regulatory Approval asserted against a
                  Defending Party, the other Party shall, at no out-of-pocket
                  expense to it except as otherwise provided in this Article 12,
                  reasonably cooperate with and provide such reasonable
                  assistance to such Defending Party as such Defending Party may
                  reasonably request in connection with its defense against such
                  Actions. Such reasonable assistance may include, without
                  limitation, providing copies of all relevant correspondence
                  and other materials that the Defending Party may reasonably
                  request, provided, however, that any Confidential Information
                  so provided shall be treated in accordance with the provisions
                  of Article 13 hereof.

         12.2     INDEMNIFICATION BY AHP. AHP shall indemnify, defend and hold
                  harmless Horizon, its Affiliates or its permitted
                  sublicensees, and each of its and their respective employees,
                  officers, directors and agents (each, a "Horizon Indemnified
                  Party") from and against any and all liability, loss, damage,
                  cost, and expense (including reasonable attorneys' fees)
                  (collectively, a "Liability") which the Horizon Indemnified
                  Party may incur, suffer or be required to pay resulting from
                  or arising in connection with (i) the breach by AHP of any
                  representation or warranty contained in this Agreement, (ii)
                  the manufacture, promotion, distribution, testing, use,
                  marketing, sale or other disposition of the Substance or
                  Products by AHP outside of the Territory and Field, whether
                  before or after the Effective Date; (iii) the manufacture,
                  promotion, distribution, testing, use, marketing, sale or
                  other disposition of the Substance or Products by AHP within
                  the Territory and Field before the Effective Date; or (iv) the
                  use of the Trademarks by AHP or its Affiliates within or
                  outside the Territory, whether before or after the Effective
                  Date. Notwithstanding the foregoing, AHP shall have no
                  obligation under this Agreement to indemnify, defend or hold
                  harmless any

                                      -21-
<PAGE>   22

                  Horizon Indemnified Party with respect to claims, demands,
                  costs or judgments which result from willful misconduct or
                  negligent acts or omissions of Horizon, its Affiliates, its
                  permitted sublicensees, or any of their respective employees,
                  officers, directors or agents.

         12.3     INDEMNIFICATION BY HORIZON. Horizon shall indemnify, defend
                  and hold harmless AHP and its Affiliates, and each of its and
                  their respective employees, officers, directors and agents
                  (each, an "AHP Indemnified Party") from and against any
                  Liability which the AHP Indemnified Party may incur, suffer or
                  be required to pay resulting from or arising in connection
                  with (i) the breach by Horizon of any representation or
                  warranty contained in this Agreement; (ii) the manufacture
                  (but only upon the commencement of Horizon's manufacturing the
                  Products pursuant to the Product Supply Agreement), promotion,
                  distribution, testing, use, marketing, sale or other
                  disposition of Products by Horizon, its Affiliates, its
                  permitted sublicensees or their respective subcontractors; or
                  (iii) the use of the Trademark by Horizon, its Affiliates, its
                  permitted sublicensees or their respective subcontractors.
                  Notwithstanding the foregoing, Horizon shall have no
                  obligation under this Agreement to indemnify, defend, or hold
                  harmless any AHP Indemnified Party with respect to claims,
                  demands, costs or judgments which result from willful
                  misconduct or negligent acts or omissions of AHP, its
                  Affiliates, its permitted sublicensees or any of their
                  respective employees, officers, directors or agents.

         12.4     CONDITIONS TO INDEMNIFICATION. The obligations of the
                  indemnifying Party under Sections 12.2 and 12.3 are
                  conditioned upon the delivery of written notice to the
                  indemnifying Party of any potential Liability promptly after
                  the indemnified Party becomes aware of such potential
                  Liability. The indemnifying Party shall have the right to
                  assume the defense of any suit or claim related to the
                  Liability if it has assumed responsibility for the suit or
                  claim in writing; however, if in the reasonable judgment of
                  the indemnified Party, such suit or claim involves an issue or
                  matter which could have a materially adverse effect on the
                  business operations or assets of the indemnified Party, the
                  indemnified Party may waive its rights to indemnity under this
                  Agreement and control the defense or settlement thereof, but
                  in no event shall any such waiver be construed as a waiver of
                  any indemnification rights such Party may have at law or in
                  equity. If the indemnifying Party defends the suit or claim,
                  the indemnified Party may participate in (but not control) the
                  defense thereof at its sole cost and expense.

         12.5     SETTLEMENTS. Neither Party may settle a claim or action
                  related to a Liability without the consent of the other Party,
                  if such settlement would impose any monetary obligation on the
                  other Party or require the other Party to submit to an
                  injunction or otherwise limit the other Party's rights under
                  this Agreement or otherwise. Except as otherwise expressly set
                  forth in this Article 12, any payment made by a Party to
                  settle any such claim or action shall be at its own cost and
                  expense.

                                      -22-
<PAGE>   23

         12.6     LIMITATION OF LIABILITY. With respect to any claim by one
                  Party against the other arising out of the performance or
                  failure of performance of the other Party under this
                  Agreement, the Parties expressly agree that the liability of
                  such Party to the other Party for such breach shall be limited
                  under this Agreement or otherwise at law or equity to direct
                  damages only and in no event shall a Party be liable for
                  punitive, exemplary or consequential damages. The limitations
                  set forth in this Section 12.6 shall not apply with respect to
                  the obligations of either Party to indemnify the other under
                  Sections 12.2 or 12.3 hereof in connection with a Liability to
                  a Third Party.

         12.7     INSURANCE. Horizon shall obtain and maintain at all times
                  during the term of this Agreement, Commercial General
                  Liability Insurance, including Products Liability Insurance,
                  with reputable and financially secure insurance carriers to
                  cover its indemnification obligations under Section 12.3, with
                  limits of not less than five million dollars ($5,000,000) per
                  occurrence and ten million dollars ($10,000,000) in the
                  aggregate. Horizon shall provide AHP with a Certificate of
                  Insurance evidencing this coverage within thirty (30) days
                  after the Closing. Such insurance policy shall name AHP as an
                  additional insured and Horizon shall use its Commercially
                  Reasonable Efforts to ensure that such insurance policy
                  contains a provision requiring ten (10) day advance
                  notification to AHP in the event of its cancellation or
                  termination. AHP shall maintain self-insurance and/or obtain
                  insurance from a Third Party insurer in amounts sufficient to
                  cover its obligations under Section 12.2. Upon Horizon's
                  written request, AHP shall provide Horizon with evidence of
                  such insurance coverage.

13.      CONFIDENTIALITY.

         13.1     NONDISCLOSURE OBLIGATION. Each of Horizon and AHP shall use
                  only in accordance with this Agreement and shall not disclose
                  to any Third Party any information including, without
                  limitation, Know-How, received by it from the other Party (the
                  "Information"), without the prior written consent of the other
                  Party. The foregoing obligations shall survive the expiration
                  or earlier termination of the last of the Transaction
                  Agreements to so expire or to be so terminated for a period of
                  five (5) years. These obligations shall not apply to
                  Information that:

                           (i)      is known by the receiving Party at the time
                                    of its receipt, and not through a prior
                                    disclosure by the disclosing Party, as
                                    documented by business records;

                           (ii)     is at the time of disclosure or thereafter
                                    becomes published or otherwise part of the
                                    public domain without breach of this
                                    Agreement by the receiving Party;

                                      -23-
<PAGE>   24

                           (iii)    is subsequently disclosed to the receiving
                                    Party by a Third Party who has the right to
                                    make such disclosure;

                           (iv)     is developed by the receiving Party
                                    independently of the Information received
                                    from the disclosing Party and such
                                    independent development can be documented by
                                    the receiving Party, or

                           (v)      is required by law, regulation, rule, act or
                                    order of any governmental authority or
                                    agency to be disclosed by a Party, provided
                                    that notice is promptly delivered to the
                                    other Party in order to provide an
                                    opportunity to seek a protective order or
                                    other similar order with respect to such
                                    Information and thereafter the disclosing
                                    Party discloses to the requesting entity
                                    only the minimum Information required to be
                                    disclosed in order to comply with the
                                    request, whether or not a protective order
                                    or other similar order is obtained by the
                                    other Party.

         13.2     PERMITTED DISCLOSURES. Information may be disclosed to
                  employees, agents, consultants, sublicensees or suppliers of
                  the recipient Party or its Affiliates, but only to the extent
                  required to accomplish the purposes of this Agreement and only
                  if the recipient Party obtains prior agreement from its
                  employees, agents, consultants, sublicensees, suppliers or
                  Third Party manufacturers to whom disclosure is to be made to
                  hold in confidence and not make use of such Information for
                  any purpose other than those permitted by this Agreement. Each
                  Party will use at least the same standard of care as it uses
                  to protect proprietary or confidential information of its own
                  to ensure that such employees, agents, consultants,
                  sublicensees, suppliers or Third Party manufacturers do not
                  disclose or make any unauthorized use of the Information.

         13.3     DISCLOSURE OF AGREEMENT. Neither Horizon nor AHP shall release
                  to any Third Party or publish in any way any non-public
                  information with respect to the terms of this Agreement or
                  concerning their cooperation without the prior written consent
                  of the other, which consent will not be unreasonably withheld
                  or delayed, provided, however, that either Party may disclose
                  the terms of this Agreement to the extent required to comply
                  with applicable laws, including, without limitation the rules
                  and regulations promulgated by the United States Securities
                  and Exchange Commission, provided, however, that prior to
                  making any such disclosure, the Party intending to so disclose
                  the terms of this Agreement shall (i) provide the
                  nondisclosing Party with written notice of the proposed
                  disclosure and a opportunity to review and comment on the
                  intended disclosure which is reasonable under the
                  circumstances and (ii) shall seek confidential treatment for
                  as much of the disclosure as is reasonable under the
                  circumstances, including, without limitation, seeking
                  confidential treatment of any information as may be requested
                  by the other Party. Notwithstanding any other provision of
                  this

                                      -24-
<PAGE>   25

                  Agreement, each Party may disclose the terms of this Agreement
                  to lenders, investment bankers and other financial
                  institutions of its choice solely for purposes of financing
                  the business operations of such Party either (i) upon the
                  written consent of the other Party or (ii) if the disclosing
                  Party uses reasonable efforts to obtain a signed
                  confidentiality agreement with such financial institution with
                  respect to such information on terms substantially similar to
                  those contained in this Article 13.

         13.4     PUBLICITY. Subject to Section 13.3, all publicity, press
                  releases and other announcements relating to this Agreement or
                  the transactions contemplated hereby shall be reviewed in
                  advance by, and shall be subject to the approval of, both
                  Parties.

14.      MISCELLANEOUS.

         14.1     FORCE MAJEURE. Neither Party shall be liable to the other for
                  delay or failure in the performance of the obligations on its
                  part contained in this Agreement if and to the extent that
                  such failure or delay is due to circumstances beyond its
                  control (including, without limitation, AHP's inability to
                  obtain, from a Third Party, sufficient quantities of the raw
                  materials needed for the manufacture of Substance to meet its
                  manufacturing obligations under Article 7) which it could not
                  have avoided by the exercise of reasonable diligence. It shall
                  notify the other Party promptly should such circumstances
                  arise, giving an indication of the likely extent and duration
                  thereof and shall use all Commercially Reasonable Efforts to
                  resume performance of its obligations as soon as practicable.

         14.2     ASSIGNMENT.

                  14.2.1   ASSIGNMENT BY HORIZON. Horizon may assign any or all
                           of its rights or obligations under this Agreement in
                           the Territory to any of its Affiliates, for so long
                           as they remain Affiliates. In addition, Horizon may
                           assign any or all of its rights or obligations under
                           this Agreement in the Territory in conjunction with a
                           merger or acquisition of Horizon or its Affiliates.
                           Horizon may not otherwise assign any of its rights or
                           obligations under this Agreement without AHP's prior
                           written consent, not to be unreasonably withheld. AHP
                           shall respond to such requests by Horizon for
                           assignment within thirty (30) days from such request.
                           Any permitted assignment shall not relieve Horizon of
                           its responsibilities for performance of its
                           obligations under this Agreement. Notwithstanding the
                           foregoing, Horizon may not assign or otherwise
                           transfer the Regulatory Approvals to any Third Party
                           until the later to occur of (i) all payments are made
                           under Article 4.1, and (ii) termination of the
                           Product Supply Agreement.

                  14.2.2   ASSIGNMENT BY AHP. AHP may assign any or all of its
                           rights or obligations under this Agreement to any of
                           its Affiliates or to any Third

                                      -25-
<PAGE>   26

                           Party, provided, however, that AHP may assign all or
                           part of its obligations to a Third Party only after
                           receiving Horizon's prior written consent, which
                           consent shall not be unreasonably withheld or
                           delayed; provided, further, that such assignment
                           shall not relieve AHP of its responsibilities for
                           performance of its obligations under this Agreement.
                           Notwithstanding the foregoing, Horizon's consent
                           shall not be required for any assignment made by AHP
                           in connection with a merger or similar reorganization
                           of AHP or its parent company or the sale of all or
                           substantially all of AHP's or AHP's parent company's
                           pharmaceutical assets.

                  14.2.3   BINDING NATURE OF ASSIGNMENT. This Agreement shall be
                           binding upon and inure to the benefit of the
                           successors and permitted assigns of the Parties. Any
                           assignment not in accordance with this Article 14
                           shall be void.

         14.3     NO WAIVER. The failure of either Party to require performance
                  by the other Party of any of that other Party's obligations
                  hereunder shall in no manner affect the right of such Party to
                  enforce the same at a later time. No waiver by any Party
                  hereto of any condition, or of the breach of any provision,
                  term, representation or warranty contained in this Agreement
                  whether by conduct or otherwise, in any one or more instances,
                  shall be deemed to be or construed as a further or continuing
                  waiver of any such condition or breach, or of any other
                  condition or of the breach of any other provision, term,
                  representation or warranty hereof.

         14.4     SEVERABILITY. If a court or other tribunal of competent
                  jurisdiction should hold any term or provision of this
                  Agreement to be excessive, or invalid, void or unenforceable,
                  the offending term or provision shall be deleted or revised to
                  the extent necessary to be enforceable, and, if possible,
                  replaced by a term or provision which, so far as practicable
                  achieves the legitimate aims of the Parties.

         14.5     RELATIONSHIP BETWEEN THE PARTIES. Both Parties are independent
                  contractors under this Agreement. Nothing herein contained
                  shall be deemed to create an employment, agency, joint venture
                  or partnership relationship between the Parties hereto or any
                  of their agents or employees, or any other legal arrangement
                  that would impose liability upon one Party for the act or
                  failure to act of the other Party. Neither Party shall have
                  any express or implied power to enter into any contracts or
                  commitments or to incur any liabilities in the name of, or on
                  behalf of, the other Party, or to bind the other Party in any
                  respect whatsoever.

         14.6     CORRESPONDENCE AND NOTICES.

                  14.6.1   ORDINARY NOTICES. Correspondence, reports,
                           documentation, and any other communication in writing
                           between the Parties in the course of ordinary
                           implementation of this Agreement shall be delivered
                           by hand,

                                      -26-
<PAGE>   27

                           sent by facsimile, overnight courier or by airmail to
                           the employee or representative of the other Party who
                           is designated by such other Party to receive such
                           written communication.

                  14.6.2   EXTRAORDINARY NOTICES. Extraordinary notices and
                           communications (including, without limitation,
                           notices of termination, force majeure, material
                           breach, change of address) shall be in writing and
                           sent by prepaid registered or certified air mail, or
                           by facsimile confirmed by prepaid registered or
                           certified air mail letter, and shall be deemed to
                           have been properly served to the addressee upon
                           receipt of such written communication.

                  14.6.3   ADDRESSES. In the case of Horizon, the proper address
                           for communications and for all payments shall be:

                                    Horizon Pharmaceutical Corporation
                                    660 Hembree Parkway, Suite 106
                                    Roswell, Georgia 30076
                                    Attn: Mr. Brent Dixon
                                    Fax: (770) 442-9594

                           and it the case of AHP, the proper address for
                           communications and for all payments shall be:

                                    Wyeth-Ayerst Laboratories
                                    555 Lancaster Avenue
                                    St. Davids, Pennsylvania 19087
                                    Attn: Senior Vice President, Global
                                          Business Development
                                    Fax: (610) 688-9498

                           with a copy to:

                                    American Home Products Corporation
                                    5 Giralda Farms
                                    Madison, New Jersey 07940
                                    Attn: Senior Vice President and General
                                          Counsel
                                    Fax: (973) 660-7156

         14.7     CHOICE OF LAW. This Agreement is subject to and governed by
                  the laws of the State of Delaware, excluding its conflict of
                  laws provisions.

         14.8     ENTIRE AGREEMENT AMENDMENT. This Agreement, together with the
                  other Transaction Agreements and the Confidential Disclosure
                  Agreement between AHP and E.J. Financial Enterprises Inc. (an
                  equity holder in Horizon) dated April 28, 1998, and all the
                  covenants, promises, agreements, warranties, representations,

                                      -27-
<PAGE>   28
                  conditions and understandings contained herein and therein
                  sets forth the complete, full and exclusive agreement between
                  the Parties and supersedes and terminates all prior and
                  contemporaneous agreements and understandings between the
                  Parties, whether oral or in writing. There are no covenants,
                  promises, agreements, warranties, representations, conditions
                  or understandings, either oral or written, between the Parties
                  other than as are set forth in the Transaction Agreements. No
                  subsequent alteration, amendment, change, waiver or addition
                  to this Agreement shall be binding upon the Parties unless
                  reduced to writing and signed by an authorized officer of each
                  Party. No understanding, agreement, representation or promise,
                  not explicitly set forth herein, has been relied on by either
                  Party in deciding to execute this Agreement.

         14.9     HEADINGS. The headings and captions used in this Agreement are
                  solely for the convenience of reference and shall not affect
                  its interpretation.

         14.10    COUNTERPARTS. This Agreement may be executed in one or more
                  counterparts each of which shall be an original and all of
                  which shall constitute together the same document.

         14.11    FURTHER ACTIONS. Each Party agrees to execute, acknowledge and
                  deliver such further instruments, and to do all other acts, as
                  may be necessary or appropriate in order to carry out the
                  purposes and intent of this Agreement including, without
                  limitation, any filings with any antitrust agency which may be
                  required.

         IN WITNESS WHEREOF, this Agreement has been executed by the duly
authorized representatives of the Parties as of the date set forth below.

AMERICAN HOME PRODUCTS              HORIZON PHARMACEUTICALS, INC.
CORPORATION

-----------------------------       --------------------------------
Name:                               Name:
Title:                              Title:

                                      -28-
<PAGE>   29

                                    EXHIBIT A

                               CUSTOMER CONTRACTS

          The Customer Contracts are listed on the following two pages.

<PAGE>   30

                                        [***] - CONFIDENTIAL TREATMENT REQUESTED

                            WYETH-AYERST LABORATORIES
                               BID ANALYSIS SYSTEM
                     CONTRACT PRODUCT PRICES BY NDC - ACTIVE

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------------------------------------
NDC:  00031-7824-63 ROBINUL TABLETS                                    PKG SIZE:  [***]
-----------------------------------------------------------------------------------------------------------------------------------
CTLG PRICE:  [***]              FACTOR COST:  [***]                                   FSS PRICE:  [***]
-----------------------------------------------------------------------------------------------------------------------------------
CURRENT BEST:  [***]            CURRENT NOMINALS:  [***]               FUTURE BEST:  [***]          FUTURE NOMINAL:  [***]
-----------------------------------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------------------------------------
GRP/CUST GRP/CUSTOMER NAME                   CITY        STATE  CLS    CONTRACT     START DATE    END DATE      SALES PRICE    DISC
-----------------------------------------------------------------------------------------------------------------------------------
<S>              <C>                        <C>          <C>    <C>    <C>          <C>          <C>            <C>   <C>     <C>
01 - NON-GUARANTEED TYPE
-----------------------------------------------------------------------------------------------------------------------------------
000000489        PUERTO RICO HOSP GROUP     SAN JUAN       PR         0000046178    11/01/1997   11/30/1998            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
791000010        HOSPITAL DEL MAESTRO       HATO REY       PR   14    0000046045    11/01/1997   11/30/1998            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
02 - GUARANTEED
-----------------------------------------------------------------------------------------------------------------------------------
000000344        PHS                        BETHESDA       MD         0000058826    10/01/1998   12/31/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000340        VETERANS STATE HOME        HINES          IL         0000046309    01/01/1998   11/30/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000355        PHS FEDERAL GOVT ACCTS     WASHINGTON     DC         0000046308    01/01/1998   11/30/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000406        MILITARY                   RADNOR         PA         0000046199    01/01/1998   11/30/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000310        VA PRIME VENDOR            RADNOR         PA         00000046196   01/01/1998   11/30/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000164        ISD (INTERNAL SVCS DEPT)   LOS ANGELES    CA         0000027546    02/01/1998   01/31/1999   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000195        NEW YORK CITY HLTH & HOS   NEW YORK       NY         0000037145    09/15/1997   09/30/2000            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000002003       STATE OF ARKANSAS          LITTLE ROCK    AR         0000043007    01/01/1998   12/31/1998   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000000027       MINNESOTA MULTI-STATE      ST. PAUL       MN         0000046643    05/01/1998   04/30/1999   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000002046       STATE OF SOUTH CAROLINA    COLUMBIA       SC         0000046472    05/01/1998   04/30/1999
-----------------------------------------------------------------------------------------------------------------------------------
0000009585       NEW PUERTO RICO HOSP       ST. DAVIDS     PA         0000047764    04/30/1998   04/27/1999            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000000253       TENET HEALTHCARE           DALLAS         TX         0000022284    09/01/1998   08/31/1999   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
000000309        HEALTH SERVS CORP AMER     BRIDGETON      MO         0000024878    10/01/1998   09/30/1999   [***]    [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000002004       STATE OF CALIFORNIA        SACRAMENTO     CA         0000057964    10/05/1998   09/30/2000            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
0000002048       STATE OF TENNESSEE         NASHVILLE      TN         0000060276    10/22/1998   07/31/1999            [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
04 - GUARANTEED W/OUT-CLAUSE
-----------------------------------------------------------------------------------------------------------------------------------
0000009341       MICH STATE UNIV AFFIL      EAST LANSING   MI         0000046646    02/01/98     01/31/99              [***]  [***]
-----------------------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   31
<TABLE>
<CAPTION>
05 - GUAR W/PRC ESC & OUT CLS
-------------------------------------------------------------------------------------------------------------------------------
GRP/CUST        GRP/CUSTOMER NAME      CITY        STATE     CLS   CONTRACT     START DATE  END DATE      SALES    PRICE   DISC %
<S>               <C>                 <C>          <C>       <C>  <C>           <C>         <C>           <C>      <C>     <C>
-------------------------------------------------------------------------------------------------------------------------------
000000407        OWEN HEALTHCARE      HOUSTON        TX           0000031263    07/01/1998   03/31/2000   [***]    [***]   [***]
-------------------------------------------------------------------------------------------------------------------------------
000000418        PACT (C/MEDMGNT)     PLYMOUTH       MN           0000046216    07/01/1998   03/31/2000            [***]   [***]
-------------------------------------------------------------------------------------------------------------------------------
</TABLE>

<PAGE>   32

                                    EXHIBIT B

                                    PRODUCTS

<TABLE>
<CAPTION>

        Country                  NDC No.                Strength              Dosage Form           Package Size
        -------                  -------                --------              -----------           ------------

        <S>                      <C>                    <C>                   <C>                  <C>
          USA                    7824-63                  1 mg                  tablets            bottles of 100
          USA                    7840-63                  2 mg                  tablets            bottles of 100
</TABLE>

<PAGE>   33

                                    EXHIBIT C

                                   TRADEMARKS

<TABLE>
<CAPTION>
          Country                      Trademark                  Registration No.               Renewal Date
          -------                      ---------                  ----------------               ------------
       <S>                             <C>                        <C>                            <C>
       United States                    Robinul                        728,458                    03/13/2002
</TABLE>

<PAGE>   34

                                    EXHIBIT D

                              SYSTEMS TRANSFER PLAN

         Pursuant to Section 3.2 of that certain License Agreement entered into
by and between Horizon Pharmaceutical Corporation ("Horizon") and American Home
Products Corporation, acting through its Wyeth-Ayerst Laboratories Division
("AHP") on January 29, 1999 (the "License Agreement"), Horizon and AHP, by
signing below, each agree that the documents identified below and attached
hereto constitute the Systems Transfer Plan. Horizon and AHP each further agree
that to the extent any of the attached documents are inconsistent with the
License Agreement or the Product Supply Agreement which also was entered into by
Horizon and AHP on January 29, 1999, the terms and conditions of the License
Agreement or the Product Supply Agreement, as applicable, shall control. The
Parties recognize that this document serves as a guideline for the transition of
responsibilities for the Product from AHP to Horizon and that, to the extent
that this Systems Transfer Plan imposes timelines which are not expressly stated
within the License Agreement or the Product Supply Agreement, the failure to
strictly adhere to any such timelines set forth in this Systems Transfer Plan
shall not constitute a breach of either the License Agreement or the Product
Supply Agreement

         Attachments

          1.      Initial inventory shipment; Outstanding sales orders; Initial
                  forecast; On-going purchase orders
          2.      Product/Quality Complaints
          3.      Labeling, Product Inserts, Tooling
          4.      Customer Contracts
          5.      Rebates
          6.      Manufacturing Plant Services
          7.      Regulatory
          8.      Returns
          9.      Chargebacks

HORIZON PHARMACEUTICAL                      AMERICAN HOME PRODUCTS
  CORPORATION                               CORPORATION acting through its
                                             Wyeth-Ayerst Laboratories Division

By:                                          By:
   ----------------------------                 -----------------------------
Name:                                        Name:
     --------------------------                   ---------------------------
Title:                                       Title:
      -------------------------                    --------------------------
Date:                                        Date:
     --------------------------                   ---------------------------

<PAGE>   35

                                    EXHIBIT E

                     ADVERSE DRUG EVENT REPORTING PROCEDURE

         The Parties hereby agree that the following terms will govern
disclosures of each Party to the other with respect to adverse event reporting
relating to the Product or Substance as clinically tested or marketed by or on
behalf of either Party.

1.       Definitions.

         1.1      An Adverse Drug Experience ("ADE") is defined as:

                   a)      any experience which is adverse, including what are
                           commonly described as adverse or undesirable
                           experiences, adverse events, adverse reactions, side
                           effects, or death due to any cause associated with,
                           or observed in conjunction with the use of a drug,
                           biological product, or device in humans, whether or
                           not considered related to the use of that product:

                           -        occurring in the course of the use of a
                                    drug, biological product or device,

                           -        associated with, or observed in conjunction
                                    with product overdose, whether accidental or
                                    intentional

                           -        associated with, or observed in conjunction
                                    with product abuse, and/or

                           -        associated with, or observed in conjunction
                                    with product withdrawal.

                  b)       Any significant failure of expected pharmacological
                           or biologic therapeutical action (with the exception
                           of in clinical trials).

         1.2      Serious or Non-Serious is defined as:

                  a)       A Serious ADE is any adverse drug experience
                           occurring at any dose that results in any of the
                           following outcomes: death, a life-threatening adverse
                           drug experience, inpatient hospitalization or
                           prolongation of existing hospitalization, a
                           persistent or significant disability/incapacity, or a
                           congenital anomaly/birth defect. Other important
                           medical events that may not result in death, be
                           life-threatening, or require hospitalization may be
                           considered a serious adverse drug experience when,
                           based upon appropriate medical judgment, they may
                           jeopardize the patient or subject and may require
                           medical or surgical intervention to prevent one of
                           the outcomes listed in this definition. Examples of
                           such medical events

<PAGE>   36

                           include allergic bronchospasm requiring intensive
                           treatment in an emergency room or at home, blood
                           dyscrasias or convulsions that do not result in
                           inpatient hospitalization, or the development of drug
                           dependency or drug abuse.

                  b)       A Non-Serious ADE is any ADE which does not meet the
                           criteria for a serious ADE.

         1.3      Life-threatening adverse drug experience is defined as any
                  adverse drug experience that places the patient, in the view
                  of the initial reporter, at immediate risk of death from the
                  adverse drug experience as it occurred, i.e., it does not
                  include an adverse drug experience that, had it occurred in a
                  more severe form, might have caused death.

         1.4      Disability is defined as a substantial disruption of a
                  person's ability to conduct normal life functions.

         1.5      An Unexpected ADE is defined as any ADE that is not listed in
                  the current labeling for the drug product. This includes
                  events that may be symptomatically and pathophysiologically
                  related to an event listed in the labeling, but differ from
                  the event because of greater severity or specificity.

         1.6      Associated with or related to the use of the drug is defined
                  as: A reasonable possibility exists that the ADE was caused by
                  the drug.

         1.7      NDA Holder is defined as: An "Applicant" as defined in 21 CFR
                  Part 314.3(b), for regulatory approval of a Product in any
                  regulatory jurisdiction, including a holder of a foreign
                  equivalent thereto.

         1.8      IND Holder is defined as: A "Sponsor" as defined in 21 CFR
                  Part 313.1 (b) of an investigational new drug in any
                  regulatory jurisdiction, including a holder of a foreign
                  equivalent thereto.

         1.9      Capitalized terms not defined in this Exhibit shall have the
                  meaning assigned thereto in the Agreement.

2.       With respect to the Product or Substance, the Parties agree as follows:

         a.       All initial reports and any follow-up information (oral or
                  written) for any and all Serious ADEs as defined above (other
                  than with respect to animal studies) which become known to
                  either Party (other than from disclosure by or on behalf of
                  the other Party) must be communicated by telephone, telefax or
                  electronically directly to the other Party and/or the NDA
                  Holder, IND Holder (individually and collectively referred to
                  as "Holders") within forty-eight (48) hours of receipt of the
                  information. Written confirmation of the Serious ADE received
                  by such Party

<PAGE>   37

                  should be sent to the other Party and/or the Holders as soon
                  as it becomes available, but in any event within forty-eight
                  (48) hours of initial report of the Serious ADE by such Party.

         b.       Both Parties shall exchange Medwatch and/or CIOMs forms and
                  other health authority reports within forty-eight (48) hours
                  of submission to any Regulatory Authority.

         c.       All initial reports and follow-up information received for all
                  Non-Serious ADEs for marketed Product which become known to a
                  Party (other than from disclosure by or on behalf of the other
                  Party) must be communicated in writing, by telefax or
                  electronically to the other Party within ten (10) days, on
                  Medwatch or CIOMs forms (where possible).

         d.       Each Party shall coordinate and cooperate with the other
                  whenever practicable to prepare a single written report
                  regarding all Serious and/or Non-Serious ADEs, provided,
                  however, that neither Party shall be obligated to delay
                  reporting of any ADE in violation of applicable law or
                  regulations regarding the reporting of ADEs.

3.       The Parties further agree that:

         a.       A written report be forwarded to the other Party within
                  forty-eight (48) hours of receipt by the Party making the
                  report, for ADEs for animal studies which suggest a potential
                  significant risk for humans;

         b.       Each Party will give the other Party a report via a print-out
                  or computer disk of all ADEs reported to it and its Affiliates
                  relating to the Product or Substance within the last year,
                  within thirty (30) days of receipt of a request from the other
                  Party but not more often than four (4) times a year;

         c.       If either Party wishes access to ADE Reports of the other
                  Party relating to the Product or Substance, upon request of
                  that Party, the other Party shall make available its ADE
                  records relating to the Product or Substance (including
                  computer disks) for viewing and copying by the other Party.
                  The Parties may discuss the transfer of ADE Reports by
                  computer disk.

         d.       Disclosure of information hereunder by a Party to the other
                  Party shall continue as long as either Party and/or its
                  Affiliates or designees continue to clinically test or market
                  Product or Substance.

4.       Each Party shall diligently undertake the following further obligations
         where both Parties are or will be commercializing the Product or
         Substance pursuant to the Agreement and/or performing clinical trials
         with respect to the Product or Substance:

<PAGE>   38

         a.       Upon the Effective Date, each Party shall identify individuals
                  who shall be responsible for identifying all ADE reporting
                  requirements in all countries of the Territory as set forth in
                  the Agreement, and any amendments thereto;

         b.       To immediately consult with the other Party, with respect to
                  the investigation and handling of any Serious ADE disclosed to
                  it by the other Party or by a third Party and to allow the
                  other Party to review the Serious ADE and to participate in
                  the follow-up investigation;

         c.       To immediately advise the other Party of any Product and/or
                  Substance safety communication received from a health
                  authority and consult with the other Party with respect to any
                  Product and/or Substance warning, labeling change or change to
                  an investigators' brochure involving safety issues proposed by
                  the other Party, including, but not limited to the safety
                  issues agreed to by the Parties;

         d.       To diligently handle in a timely manner the follow-up
                  investigation and resolution of each ADE reported to it;

         e.       To provide the other Party mutually agreed upon audit rights
                  of its ADE reporting system and documentation, upon prior
                  notice, during normal business hours, at the expense of the
                  auditing Party and under the confidentiality obligations set
                  forth in the Agreement;

         f.       To meet in a timely fashion from time to time as may be
                  reasonably required to implement the adverse event reporting
                  and consultation procedures described in this Exhibit E,
                  including identification of those individuals in each Party's
                  Drug Safety group who will be responsible for reporting to and
                  receiving ADE information from the other Party, and the
                  development of a written standard operating procedure with
                  respect to adverse event reporting responsibilities, including
                  reporting responsibilities to investigators;

         g.       Where possible, to transmit all data electronically;

         h.       To report to each other any addenda, revisions or changes to
                  the Agreement (e.g., change in territories, local regulations,
                  addition of new licensors/licensees to the Agreement, etc.)
                  which might alter the adverse event reporting responsibilities
                  hereunder;

         i.       To utilize English as the language of communication and data
                  exchange between the Parties;

         j.       To develop a system of exchange of documents and information
                  in the event that the Agreement involves more than two
                  Parties;

         k.       To work together to develop an electronic system to transmit
                  ADE data.

                                      -32-
<PAGE>   39

5.       The Parties may meet after the Effective Date of the Agreement to
         establish a separate agreement for adverse event exchange which will
         supersede this Exhibit E.

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