<PAGE>   1
                                                                   EXHIBIT 10.15

                         CONFIDENTIAL TREATMENT REQUEST
                         ------------------------------


     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.


                             DISTRIBUTION AGREEMENT

between
                           G. Pohl Boskamp GmbH & Co.
                           Kieler Strasse 11
                           D-25551 Hohenlockstedt
                           Federal Republic of Germany
                           represented by Mrs. Marianne Boskamp, General Manager
                           of the Company

                                              -hereinafter referred to as "POHL"

and
                           HORIZON Pharmaceutical Corporation
                           660 Hembree Parkway, Suite 106
                           Roswell, GA 30076/USA
                           represented by Dr. Mahendra Shah,
                           Chairman of the Board

                                           -hereinafter referred to as "HORIZON"


Preamble

POHL intends to appoint a new distributor for the Territory as defined in ss.3
hereinafter HORIZON is willing to become a distributor for POHL Now, therefore,
the parties agree upon the following terms and conditions:

                                      ss.1
                             Object of the Agreement

1.1  POHL hereby appoints HORIZON as its distributor to promote the PRODUCTS of
     POHL as defined ss.2 in the Territory as defined ss.3. HORIZON shall


                                       1
<PAGE>   2


have exclusive rights in the Territory to distribute, market and sell the
PRODUCTS and other products of POHL with the same active ingredient and the same
route of administration. In case that POHL wants to market other Nitroglycerin
Products in the Territory POHL has to offer the Products to HORIZON. HORIZON has
to give his final decision within 90 days to this offer. In case HORIZON is not
interested in the distribution of these products or has not informed POHL in
writing within 90 days after receipt of the offer about its interest in the
distribution of the products so is POHL free to transfer the distribution rights
for these products in the Territory to a third party. This is also valid
provided HORIZON has stated its interest in due time but both parties have not
agreed upon the terms (for instance price, minimum sales quantities) within 6
months after receipt of the offers.

1.2  HORIZON agrees to buy the PRODUCTS which are destined for distribution in
     the Territory only from POHL.

1.3  HORIZON shall buy and sell POHL's PRODUCTS in its own name and for its own
     account and acknowledges that it has no authority to act for or on behalf
     of POHL except as otherwise specifically set forth herein. HORIZON is not
     entitled to entrust third persons with any rights or claims deriving from
     this Agreement without prior written consent of POHL. POHL hereby agrees
     that HORIZON may engage under the following preconditions a third party to
     distribute, market and sell the PRODUCTS in Puerto Rico and Caribbean
     Islands. Provided HORIZON intends to appoint a third party with the
     distribution of the PRODUCTS in Puerto Rico or Caribbean Islands so this
     party should also be bound by the contents of this Distribution Agreement.
     HORIZON shall guarantee this commitment and provide POHL with a copy of the
     corresponding agreement. Upon written approval of this agreement by POHL
     HORIZON is authorized to entrust a third party with the distribution rights
     for the territories Puerto Rico and Caribbean Islands. Also in this case
     HORIZON is still exclusive responsible according to this Agreement and
     especially the breaches of duty by the third party which may give a cause
     for the termination of this Agreement should be imputed to HORIZON. As

                                       2
<PAGE>   3


     independent contractor, HORIZON shall incur all expenses and costs of
     -including without limitation - its office overhead, travel costs,
     telephone, telefax, sales promotion and advertising costs. POHL shall not
     be responsible for any portion of such expenses except as otherwise set
     forth herein.

1.4  POHL agrees to refer to HORIZON all inquiries from the Territory received
     by POHL with respect to the PRODUCTS.

                                      ss.2
                                    Products

The term "PRODUCTS" refers to all finished products listed on SUPPLEMENT I which
shall include samples ("The PRODUCTS") presently manufactured and sold by POHL.
SUPPLEMENT I may be amended in future for additions of products by mutual
consent of POHL and HORIZON. Upon mutual consent of POHL and HORIZON, such
products will become "PRODUCTS" for distribution of which this Agreement shall
apply accordingly.

                                      ss.3
                                    Territory

The Territory is the geographical area of the countries listed on SUPPLEMENT II.

                                      ss.4
                                Duties of HORIZON

4.1  HORIZON shall exert best efforts to take advantage of all possibilities to
     sell the PRODUCTS in the Territory and to maintain a continuous, full-time
     in-Territory representation.

4.2  HORIZON further agrees


                                       3
<PAGE>   4

     -    to maintain an effective sales organization within the Territory in
          order to protect the distribution interests of HORIZON and POHL;

     -    to always have quantities of the PRODUCTS in stock sufficient to cover
          three months of foreseeable sales in the Territory subject to PRODUCT
          being supplied by POHL in accordance with HORIZON'S orders;

     -    to report regularly monthly its total stock position, turn-over
          figures and sample movements as well as all important news on the
          pharmaceutical market in the Territory, especially with regard to
          competitive products and the price structure in the Territory and any
          changes thereof. Monthly reports shall reach POHL by the tenth day of
          each following month;

     -    to make the appropriate advertising and publicity in accordance with
          ss.9;

     -    to employ trained personnel in a sufficient number for the sale and
          distribution of the PRODUCTS;

     -    to buy from POHL minimum quantities of the PRODUCTS as specified in
          SUPPLEMENT III to this Agreement;

     -    to notify POHL in writing prior to making any substantial operational
          changes in personnel, ownership, legal structure, country of operation
          and products represented by HORIZON;

     -    to sell the PRODUCTS only with the trademark of POHL and/or the
          business logo and the original packaging and/or presentation of POHL,
          HORIZON'S trade dress (logo and address) are added;


                                       4
<PAGE>   5

     -    to report to POHL at the beginning of a calendar's quarter - no later
          than the 3rd day of the calendar's quarter the planned sales figures
          projected for the PRODUCTS for the next 12 months.

4.3  HORIZON is not entitled to

     -    produce or sell - neither directly nor indirectly - products which
          contain any organic nitrates or any products that are indicated for
          relief of angina pectoris, with the exception of the under ss.5.1
          mentioned products;

     -    solicit customers outside the Territory for the PRODUCTS, to establish
          and/or maintain branch offices and/or storage depots outside the
          Territory.

                                      ss.5
                         Distribution of Other Products

5.1  At the signature hereof, HORIZON produces or sells the following
     competitive products containing following active ingredient.

5.2  The list of competitive products under ss.5.1 can only be extended with the
     prior written consent of POHL which should be applied for before
     distribution of these products.

5.3  In the event that a generic of a PRODUCT or a pump or spray product
     containing the active ingredient of a PRODUCT is marked in the Territory by
     an entity other than HORIZON, the parties shall in good faith agree upon a
     reduced royalty rate and reduced minimum purchase requirements for such
     PRODUCT.


                                       5
<PAGE>   6

                                          [***]-CONFIDENTIAL TREATMENT REQUESTED

                                      ss.6
                    Purchase of PRODUCTS/Obligations of POHL

6.1  HORIZON shall be entitled to purchase the PRODUCTS on the basis of POHL's
     general terms and conditions of sale applicable from time to time. The
     terms and conditions of sale of POHL valid at present are attached hereto
     as SUPPLEMENT IV.

6.2  POHL will, according to its general terms and conditions of sale, exert
     best efforts to carry out the orders of HORIZON carefully and punctually.
     In case that POHL is not able to execute an order in time totally or only
     partially, it will notify HORIZON immediately; and if, as a result of such
     inability, HORIZON does not meet minimum purchase requirement(s), HORIZON
     shall not be in breach nor may POHL terminate this Agreement.

6.3  The purchase price for the respective PRODUCTS is the price listed on
     SUPPLEMENT I.

6.4  POHL and HORIZON may mutually agree in writing to modify the terms and
     conditions of sale. POHL may increase the price of the PRODUCTS to HORIZON
     on an annual basis by the costs of raw materials and direct labor with such
     increases being limited to [***] per annum. Additional price increases
     caused by extraordinary circumstances will be discussed and mutually agreed
     upon prior to increase.

6.5  Payment of the deliveries has to be made in net within 30 days after
     receipt of goods in Deutsche Marks. POHL will invoice all of its deliveries
     of PRODUCTS as of 01.01.2002 in Euro currency. Payments of the deliveries
     have to be made as of 01.01.2002 in net within 30 days after receipt of
     goods in Euro currency. The conversion of Deutsche Marks into Euro shall be
     made on the basis of the official exchange rate. The parties agree that the
     currency conversion of Deutsche Marks into Euro will not have any effect on


                                       6
<PAGE>   7

     the validity of the Distribution Agreement and not to entitle any party to
     renegotiate the prices for the PRODUCTS listed in SUPPLEMENT I. Payment of
     Royalties are done quarterly through wire 45 days after end of each
     quarter.

6.6  HORIZON fixes its sales price for the PRODUCTS within the Territory at its
     own discretion. POHL, however, will give a not binding recommendation on
     the sales price for the PRODUCTS which will be discussed with HORIZON.
     HORIZON and POHL will take into account that the competitiveness of the
     PRODUCTS has to be maintained as far as possible. HORIZON undertakes to
     notify POHL of all changes in prices and in the event of a change to
     provide POHL with corresponding price lists.

6.7  Any claim of HORIZON concerning POHL's deliveries of PRODUCTS shall be
     considered by POHL only in the event that such claim reaches POHL by
     registered mail or telefax with confirmed letter within 30 days calculated
     from the date of delivery arrival at the first port of the Territory.

6.8  The PRODUCTS, when shipped to HORIZON, shall confirm to the specifications
     for said PRODUCTS, be free from defects in materials and comply with all
     applicable laws of and within the Territory including the current Good
     Manufacturing Practices of the United States Food and Drug Administration.

6.9  If POHL does not have enough raw materials to meet the order requirements
     of HORIZON and the requirements for other product(s) containing the same
     raw material, POHL shall apportion such raw material based on the previous
     12 months sales of such products.

6.10 HORIZON may order PRODUCTS to be shipped 120 days from such order. POHL
     shall have no obligation to ship PRODUCTS before the 120 days.


                                       7
<PAGE>   8

                                      ss.7
                      Registration/German Food and Drug Law


7.1  For the life of this Agreement, POHL grants to HORIZON the right to utilize
     POHL's product registrations in the Territory in accordance with ss.2. POHL
     undertakes to maintain the existing product registrations in the Territory.
     HORIZON agrees to assist POHL in maintaining registrations and registering
     new products, which are added to this Agreement pursuant to ss.2, in every
     respect. HORIZON shall in particular give POHL advice concerning the
     preparation of the set of necessary registration documents as provided for
     in the laws valid in the Territory at the relevant time, and POHL shall
     provide the respective documents in English as far as available against
     receipt and free of charge.

7.2  All respective necessary formalities and steps required by the competent
     health authorities of the Territory shall be effected by HORIZON in the
     name and after prior written authorization by POHL.

7.3  If the law of the Territory necessitates the registrations to be in
     HORIZON's name or as far as the registrations for the individual products
     in the Territory have been arranged to be in HORIZON's name, then HORIZON
     hereby agrees irrevocably and unconditionally to surrender such
     registrations and the rights connected therewith to POHL immediately and
     unconditionally when the cancellation of this Agreement becomes effective
     or the Agreement terminates.

7.4  All registration fees of a successfully registered product shall be
     refunded by POHL to HORIZON against presentation of the approval documents
     and other evidence.

7.5  HORIZON shall arrange for any necessary translation to/from the language of
     the Territory. POHL shall reimburse to HORIZON such expenses against
     evidence.

                                       8
<PAGE>   9

     HORIZON affirms that it is not entitled to any claims against POHL for
     compensation or indemnity in case of a fruitless registration attempt other
     than those for fees for said fruitless registration attempt charged by the
     competent national health authority of the Territory and hereby renounces
     to any possible claim against POHL which accepts the renunciation.

7.6  HORIZON is not allowed to use any registration documentation outside the
     Territory.

7.7  HORIZON further undertakes to comply with German Drug Law which requires
     also from a distributor abroad that HORIZON reports to POHL any case of
     actual or suspected side reactions or interactions which become known in
     connection with POHL's delivered PRODUCTS.


                                      ss.8
                           Scientific Use of PRODUCTS

8.1  In case that the PRODUCTS of POHL are used for scientific studies in the
     Territory which are or might be intended for publication, it shall be the
     duty of HORIZON to get in touch and keep close contact with the respective
     scientists and to effect coordination with POHL particularly in stages of
     protocol planning and of formulating results prior to actual publication.
     This duty refers to all such studies regardless of whether PRODUCTS may be
     involved alone or together with other drugs or placebos or regardless of
     whether the initiative may have come to the knowledge of HORIZON through
     the manufacturer and/or a third party.

8.2  HORIZON undertakes not to start, initiate or allow such studies without the
     prior written authorization of POHL, which shall not be unreasonably
     withheld and POHL's response to HORIZON'S request for the same shall be
     given in a timely manner. Any such studies which are or may be already in
     process, unauthorized or not, shall be reported to POHL immediately when
     coming known to HORIZON and shall be followed up as specified above.




                                       9
<PAGE>   10

                                      ss.9
                             Advertisement/Publicity


9.1  POHL agrees to provide to HORIZON prospectuses for the PRODUCTS,
     respectively drafts hereof, and reports of scientific tests as far as
     available in respect of the PRODUCTS at no charge to HORIZON.

9.2  HORIZON undertakes to make continuous publicity for the PRODUCTS, in
     particular by visiting medical specialists, by advertising in medical
     journals and using pamphlets. For visiting medical specialists, HORIZON
     shall keep available at all times a sufficient number of qualified
     full-time representatives. A print proof of all advertising material shall
     be sent to POHL immediately after completion.

9.3  Any and all expenses of any advertising and/or publicity shall be borne by
     HORIZON.


                                      ss.10
                          Presentations and Trademarks

10.1 HORIZON shall distribute the PRODUCTS only in the original product outfit
     and packaging prescribed by POHL. Modifications of the original product
     outfit and packaging are only allowed for serious reasons and with the
     prior written consent of POHL. The PRODUCTS, labels, packaging,
     presentations and product inserts shall have also HORIZON's trademark and
     logo, which items shall be approved by POHL which approval shall not be
     unreasonably withheld.


                                       10
<PAGE>   11

10.2 This Agreement does not confer upon HORIZON and HORIZON will not claim any
     proprietary interest or other rights in any trademark, trade name, slogan,
     logo, copyright, design, inventory, product outfit or discovery owned or
     controlled by POHL. POHL acknowledges that all promotional materials,
     training materials, studies in connection with the PRODUCTS developed or
     undertaken for or by HORIZON are sole property of HORIZON. HORIZON
     acknowledges that all trademarks, trade names and product outfits in
     connection with the PRODUCTS are sole property of POHL.

10.3 As soon as HORIZON gets knowledge that a presentation or trademark of POHL
     used for the PRODUCTS is imitated or illegally used by a third person in
     the Territory or in case of infringement of any industrial or intellectual
     property right of POHL in the Territory, HORIZON will inform POHL
     immediately. In such event POHL will either take the necessary steps to
     prevent such misuse or authorize HORIZON to do the same. HORIZON agrees to
     cooperate with POHL and to take all necessary steps to protect the
     industrial or intellectual property rights of POHL at POHL's expense upon a
     respective written request by POHL.


                                      ss.11
                                     Secrecy

11.1 All data, literature, information and know how in any form, not in the
     public domain, that is transferred by POHL to HORIZON within the scope of
     this Agreement will be considered as confidential data. HORIZON undertakes
     to keep secret all data, literature, information and know how regarding the
     PRODUCTS, especially concerning their formulations and the know how of the
     manufacturing techniques. HORIZON is not allowed to make use of any such
     data, literature, information and know how itself nor to render them
     available nor to reveal or transfer such data, literature, information and
     know how to third parties even after the expiration of this Agreement.

                                       11

<PAGE>   12

11.2 HORIZON has to return all data, literature, information and know how in its
     possession which was made available to it within the framework of this
     Agreement to POHL within 30 days after the termination of this Agreement.
     In case that HORIZON receives such documents from third parties especially
     from the registration authorities - after the 30-day period, it has to
     return them to POHL or a person appointed by POHL immediately after receipt
     of such document.


                                      ss.12
                        Term of the Agreement/Termination

12.1 This Agreement becomes effective on February 1, 20000 and has a term of
     five (5) years. It will be renewed for an additional five-year period after
     mutual agreement on new minimum sales which reflect the market situation.

12.2 A termination has to be effected by one contractual party to the other by
     means of a registered letter/return receipt.

12.3 This Agreement may be terminated for cause. A cause shall be given if:

     a)   a petition in bankruptcy or for institution of composition proceedings
          with respect to one of the contractual parties is filed or if a
          contractual party is liquidated of if a trustee is appointed, provided
          that in an involuntary bankruptcy proceeding, such right of
          termination shall only become effective if the proceeding is not
          dismissed within 90 days of the filing;

     b)   HORIZON does not fulfill the minimum sales quantity requirement of a
          twelve-month-period as set forth in ss.4.2 unless HORIZON pays the
          difference between the minimum unit sales and the actual unit sales
          (difference in units multiplied by invoice price as defined in
          Supplement l/1), but only in the case that the actual sales are not


                                       12
<PAGE>   13

          less than minimum sales minus 30%. However, if HORIZON does not make
          the minimum sales during the next twelve-month period POHL can
          terminate the agreement;

     c)   a party has not cured a breach of this Agreement within a period of at
          least 90 days after receiving notice in writing by the other party to
          cure such breach;

     d)   HORIZON comes under direct or indirect influence or control of a
          competitor of the PRODUCTS of POHL or such competitor gains the right
          to receive information on the distribution of the PRODUCTS as a result
          of a contract or an agreement with HORIZON. Provided POHL has given
          its written approval HORIZON is allowed to take over small competitors
          and to control them in foreign countries in which POHL does not
          distribute its PRODUCTS. POHL shall give its decision within 30 days
          after the receipt of the information.

     e)   any other change (direct or indirect) of HORIZON'S shareholders or
          management occurs, unless POHL has given its consent in writing. The
          consent may not be withheld if the interests of POHL are not affected.

     f)   the PRODUCTS are not approved for distribution, marketing and sale in
          the Territory by the United States Food and Drug Administration by the
          date that is 3 (three) months after the effective date of this
          Agreement. However approval for the 75 dose PRODUCT may be after 3
          months after the effective date of this Agreement.

     If a cause is given, POHL may terminate this Agreement either with
     immediate effect or with any period up to 3 months.


                                       13
<PAGE>   14

                                      ss.13
                                  Force Majeure

The parties hereto shall not be liable for any damage if the performance of all
or parts of this Agreement is hindered or prevented by causes beyond the
performing party's control and without its fault or negligence, including but
not limited to acts of God or of public enemy, nuclear incidents, acts, laws,
orders or regulations of any government or department or agency thereof acting
in either its sovereign or contractual capacity, fires, floods, epidemics,
quarantine restrictions, strikes, work stoppages, slowdowns or other job
actions, freight embargoes, shortages of fuel or other items, delays in
transportation, boycotts, unusually severe weather and riots, insurrections,
revolutions, wars or other civil or military disturbances.


                                      ss.14
                              Written Requirements

14.1 This Agreement sets forth in writing all agreements and understandings
     between POHL and HORIZON except for the Confidentiality Agreement between
     the parties. Verbal agreements do not exist. All previous agreements or
     arrangements (if any) between the parties, written or oral, relating to the
     subject matter hereof are hereby cancelled and superseded, except for the
     Confidentiality Agreement between the parties.

14.2 Modifications and changes of this Agreement, including this clause, require
     a written form.

14.3 As for the rest POHL's general terms and conditions of trade for export
     (SUPPLEMENT IV) are applicable insofar as other terms have not been
     specific stipulated by the two parties in this Agreement.


                                       14
<PAGE>   15

                                      ss.15
                                     Notices


All notices will be deemed to have been given when posted by certified or
registered mail, return receipt, courier express or when receipt of a facsimile
or telex has been acknowledged to the following address:

         If to POHL:                G. Pohl-Boskamp GmbH & Co.
                                    Kieler Strasse 11
                                    D-25551 Hohenlockstedt
                                    Federal Republic of Germany

                                    Facsimile:  ++49 (4826) 59-161

         If to Horizon:             HORIZON Pharmaceutical Corporation
                                    660 Hembree Parkway, Suite 106
                                    Roswell, GA 30076
                                    USA

                                    Facsimile:  (770) 442-9594

If notice is personally delivered, the individual accepting such notice, if
requested, will sign a duplicate of the notice to evidence receipt thereof.


                                      ss.16
                               Partial Invalidity

Should any of the provisions of this Agreement be or become invalid, this shall
not prejudice the validity of the remaining provisions of this Agreement. The
same shall apply if it turns out that this Agreement contains any gap in its
regulations. Any such invalid provision shall be replaced or a gap in the
regulation shall be filled by a provision which legally and economically comes
closest to the desired purpose and intent of the invalid provision or fills the
gap in a way in which the parties would have filled it if they had been aware of
the gap. The parties to this Agreement undertake to agree on a relevant
amendment or adaptation of this Agreement.



                                       15
<PAGE>   16

                                      ss.17
                           Applicable Law/Jurisdiction

17.1 This Agreement is construed in accordance with and shall exclusively be
     governed by the laws of the Federal Republic of Germany.

17.2 All disputes arising out of or relating to this Agreement shall be
     submitted to the exclusive jurisdiction of the courts of Hamburg, Federal
     Republic of Germany.



Date/Place                              Date/Place

Hohenlockstedt, July 22, 1999           Roswell, Georgia - July 22, 1999

----------------------------------      ----------------------------------------
G. Pohl-Boskamp GmbH& Co.               HORIZON Pharmaceutical Corp.


----------------------------------      ----------------------------------------
N. Klapszus         G. Brinkmeier,      Mahendra G. Shah
Vice President -    Director -          Chariman of the Board
Legal Affairs       Marketing
and Business        International
Management



                                       16
<PAGE>   17


                                          [***]-CONFIDENTIAL TREATMENT REQUESTED
                                                                   July 22, 1999
                                                                   GB/Mu

SUPPLEMENT I/1

to the

DISTRIBUTION AGREEMENT dated 22/07/1999
---------------------------------------

between
                                    G. Pohl-Boskamp GmbH & Co.
                                    Kieler Strasse 11
                                    D-25551 Hohenlockstedt
                                    Federal Republic of Germany
                                    represented by Mrs. Marianne Boskamp,
                                    General Manager of the Company

and
                                    HORIZON Pharmaceutical Corporation
                                    660 Hembree Parkway, Suite 106
                                    Roswell, GA 30076/USA
                                    represented by Dr. Mahendra Shah,
                                    Chairman of the Board

Definition of the PRODUCT/s and its PRICE/s

<TABLE>
<CAPTION>
                                        Invoice Price      Terms of Delivery
                                        -------------      -----------------
<S>                                     <C>                <C>

a) NITROLINGUAL Pumpspray, 200 doses    DM [***]           C I F MIAMI, Florida
b) NITROLINGUAL Pumpspray, 75 doses     DM [***]           C I F MIAMI, Florida
                                                           Launch after approval

Units exceeding quantities ex factory as specified below
up to 30%           a) 200's            DM [***]           C I F MIAMI, Florida
                    b) 75's             DM [***]           C I F MIAMI, Florida

Units exceeding quantities ex factory as specified below
by more than 30%    a) 200's            DM [***]           C I F MIAMI, Florida
                    b) 75's             DM [***]           C I F MIAMI, Florida
</TABLE>

plus  [***]  royalties  on  net  sales  (amount  net  of  returns,  rebates  and
chargebacks)  realized  by HORIZON by selling  the  PRODUCTS  in the  Territory.
HORIZON  shall  render  quarterly  to POHL a report of the monthly  sales.  This


                                       17
<PAGE>   18

                                          [***]-CONFIDENTIAL TREATMENT REQUESTED


report shall contain the whole quantity of sales units, the gross turnover, the
discounts, the net turnover and the royalties resulting hereof. The sales to
Puerto Rico and the Caribbean Islands shall be separately specified in the
reports.

<TABLE>
<CAPTION>
Minimum Quantifies ex factory in packts/200's - 75's:
-----------------------------------------------------
<S>                                         <C>

1st year:                                   [***] units

2nd year:                                   [***] units

3rd year:                                   [***] units

4th year:                                   [***] units

5th year:                                   [***] units
</TABLE>





For and on behalf of                         For and on behalf of

G. POHL-BOSKAMP GmbH& Co.                    HORIZON Pharmaceutical Corp.



---------------------------------            ----------------------------------
N. Klapszus         G. Brinkmeier,           Mahendra G. Shah
Vice President -    Director -               Chairman of the Board
Legal Affairs and   Marketing International
Business Management


Hohenlockstedt, July 22, 1999                Roswell, Georgia - July 22, 1999
GB/Mu


                                       18
<PAGE>   19



                                                                   July 22, 1999
                                                                           GB/Mu

SUPPLEMENT II/1

to the
DISTRIBUTION AGREEMENT dated 22/07/1999
---------------------------------------

between
                    G. Pohl-Boskamp GmbH & Co.
                    Kieler Strasse 11
                    D-25551 Hohenlockstedt
                    Federal Republic of Germany
                    represented by Mrs. Marianne Boskamp, General Manager
                    of the Company

and
                    HORIZON Pharmaceutical Corporation
                    660 Hembree Parkway, Suite 106
                    Roswell, GA 30076/USA
                    represented by Dr. Mahendra Shah,
                    Chairman of the Board

Definition of HORIZON'S Territory:
----------------------------------

The Territory is the geographical area of

               U S A
               Puerto Rico,
               Caribbean islands

and

For and on behalf of                         For and on behalf of

G. POHL-BOSKAMP GmbH& Co.                    HORIZON Pharmaceutical Corp.



---------------------------------            ----------------------------------
N. Klapszus         G. Brinkmeier,           Mahendra G. Shah
Vice President -    Director -               Chairman of the Board
Legal Affairs and   Marketing International
Business Management


Hohenlockstedt, July 22, 1999                Roswell, Georgia - July 22, 1999
GB/Mu


                                       19

<PAGE>   20


                                          [***]-CONFIDENTIAL TREATMENT REQUESTED


SUPPLEMENT III/1

to the
DISTRIBUTION AGREEMENT dated 22/07/1999
---------------------------------------

between
                  G. Pohl-Boskamp GmbH & Co.
                  Kieler Strasse 11
                  D-25551 Hohenlockstedt
                  Federal Republic of Germany
                  represented by Mrs. Marianne Boskamp, General Manager
                  of the Company

and
                  HORIZON Pharmaceutical Corporation
                  660 Hembree Parkway, Suite 106
                  Roswell, GA 30076/USA
                  represented by Dr. Mahendra Shah,
                  Chairman of the Board

Definition of the PRODUCT and their minimum sales in the Territory, during a 5
year's period after launch

                                         Minimum Sales in packs
                                         in the Territory:
                                         -----------------

PRODUCT/S
NITROLINGUAL Pumpspray, 200 doses/75 doses

1st year:               [***] units

2nd year:               [***] units

3rd year:               [***] units

4th year:               [***] units

5th year:               [***] units



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For and on behalf of                         For and on behalf of

G. POHL-BOSKAMP GmbH& Co.                    HORIZON Pharmaceutical Corp.



---------------------------------            ----------------------------------
N. Klapszus         G. Brinkmeier,           Mahendra G. Shah
Vice President -    Director -               Chairman of the Board
Legal Affairs and   Marketing International
Business Management


Hohenlockstedt, July 22, 1999                Roswell, Georgia - July 22, 1999
GB/Mu


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<PAGE>   22




SUPPLEMENT IV

General Terms and Conditions of Trade (Foreign)
G. Pohl-Boskamp GmbH & Co. (Seller)

1.   Validity

     All our agreements and offers are subject to the following Conditions,
     which are accepted as soon as an order is placed, a delivery accepted, or a
     payment made, and shall also apply to any future orders placed with us.
     Deviations from our General Terms and Conditions of Trade and price lists,
     in particular any conditions used by Buyer, shall only apply if confirmed
     by us in writing. They shall not bind us even if they have not been
     explicitly rejected.

2.   Orders

     Any orders placed shall be binding on Buyer, but shall bind us only when
     they are accepted by us in writing, or when goods are handed over, or when
     the goods and the invoice are dispatched.

3.   Delivery Times

     Any delivery date quoted shall be approximate and non-binding. We shall be
     entitled to make part deliveries and submit partial invoices. Execution of
     orders on schedule is subject to our ability to deliver. Any circumstances
     which impair the delivery or distribution of our products as set down in
     the contract or which appear to jeopardize payment shall exempt us from our
     supply commitment and shall entitle us to cancel the agreed order, to the
     exclusion of further liability, wherever delivery has not yet been made.

4.   Prices

     The prices charged shall be those applicable on the day of delivery.

5.   Payment and Default

     Any obligations to pay shall be deemed to have been met only when we can
     finally dispose of the proceeds of our claim. The amount shall be due as
     agreed on, see ss. 6,5. Any delay in payment - in particular where credit
     has been granted - shall be subject to default interest at a rate max. 4%
     above the then current discount rate of the German Bundesbank, not
     excluding further claims. Any delay in payment shall entitle us to withdraw
     from any manufacturing or supply commitments not yet performed. In the
     event that Buyer is in default with payment of an invoice amount, all other
     invoices still outstanding shall be due and payable with immediate effect.
     Cheques are only accepted "due payment provided".

6.   Defences.

     Buyer shall have no right of set-off or right of retention in respect of
     any counterclaims which have not been recognized by us or by the courts.

7.   Passing of Risk.

     The risk of accidental loss, deterioration or similar obstacles to
     performance shall pass to Buyer upon the goods leaving the factory. Where
     shipment of any merchandise ready for dispatch is delayed for reasons for
     which we are not answerable, the risk shall pass upon receipt of an advice
     of dispatch.


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8.   Warranty.

     Complaints of whatever kind regarding deliveries and invoices shall only be
     considered if forwarded to us at once in writing - in the case of obvious
     defects, no later than 7 days after receipt, in the case of non-obvious
     defects, as soon as they are detected. In the case of justified complaints
     we shall, within a reasonable term, deliver merchandise free of defects to
     replace any goods subject to complaint, or shall reimburse the value of the
     goods. Buyer may assert no further claims. Any returns made without our
     prior written consent shall be neither reimbursed nor sent back or stored;
     we shall have the right to refuse acceptance.

9.   Compensation

     Compensation based on impossibility of performance, default, positive
     breach of an obligation, culpa in contrahendo or tort shall be excluded
     unless such claims are based on intent or gross negligence on our part. In
     this case, Buyer shall have a right to cancel the agreed order, to the
     exclusion of all other claims.

10.  Retention of Title, Assignment of Claims

     We shall retain title to the merchandise, incl. a rebate in kind, pending
     payment in full of all, incl. future claims of our company against Buyer
     from the business relationship. Buyer may dispose of the merchandise in the
     normal course of business, but shall neither pledge nor assign the goods as
     security. Any attachments made at the instance of third parties against
     Buyer from the resale of the goods are assigned to us herewith by way of
     security. In the event that the goods are sold by Buyer together with other
     merchandise not belonging to us, the assignment of the claim to the
     purchase price shall be limited to the amount of the proceeds for our goods
     from the resale. We undertake to release any security that exceeds the
     value of the claims to be secured by more than 25%. Subject to revocation,
     Buyer is empowered to collect the claims from the resale. Upon demand,
     Buyer shall inform us of the debtors behind the assigned claims and shall
     notify them of the assignment.

11.  Place of Performance

     Place of performance for all contractual obligations, incl. warranty, shall
     be the seat of our company.

12.  Jurisdiction, Applicable Law

     Any disputes arising from the business relationship shall be subject to the
     law of the Federal Republic of Germany, to the exclusion of the unitary
     laws on the international sale of goods and on the formation of sales
     contracts for the international sale of goods. Place of jurisdiction shall
     be Hamburg.

13.  Final Provisions

     Should any provision be invalid, this shall not affect the validity of the
     remaining provisions. The invalid provision shall be reinterpreted to make
     a valid provision in such a way as to achieve the economic intent of the
     invalid provision.



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