Document:

EXHIBIT 10.1

   CONFIDENTIAL MATERIAL OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
              EXCHANGE COMMISSION. ASTERISKS DENOTE SUCH OMISSIONS.

                  COPROMOTION AND FUTURE DEVELOPMENT AGREEMENT

                                     BETWEEN

                            KOS PHARMACEUTICALS, INC.

                                       AND

                         DUPONT PHARMACEUTICALS COMPANY

                                   May 3, 2000

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                                Table of Contents

1. Definitions..............................................................1
    1.1         Adverse Event(s)............................................1
    1.2         Affiliate...................................................1
    1.3         Business Day................................................2
    1.4         Cost Of Distribution........................................2
    1.5         Cost Of Manufacture.........................................2
    1.6         Development Committee.......................................2
    1.7         Effective Date..............................................2
    1.8         FDA.........................................................2
    1.9         Joint Copromotion Activities................................2
    1.10        Joint Marks.................................................2
    1.11        Kos Trademark...............................................2
    1.12        Know-How....................................................2
    1.13        Marketing Committee.........................................3
    1.14        Minimum Product Details.....................................3
    1.15        NDA.........................................................3
    1.16        Net Operating Profit........................................3
    1.17        Net Sales...................................................3
    1.18        Other Copromotion Activities................................3
    1.19        Party(ies)..................................................3
    1.20        Patents.....................................................3
    1.21        Product.....................................................4
    1.22        Product Detail(s)...........................................4
    1.23        Product Development Costs...................................4
    1.24        Safety Surveillance Cost....................................4
    1.25        Shared Copromotion Expenses.................................4
    1.26        Term........................................................5
    1.27        Territory...................................................5
    1.28        Third Party(ies)............................................5
    1.29        Year........................................................5
2. Grant of Rights..........................................................5
3. Term, Termination and Renegotiation......................................5
    3.1         Term........................................................5
    3.2         Early Termination...........................................5
    3.3         Renegotiation...............................................6
4. Fees and Payments........................................................6
    4.1         Stock Purchase Agreement....................................6
    4.2         Fees........................................................6
    4.3         Reimbursements..............................................6
    4.4         Product Profits.............................................6
    4.5         Payments....................................................7
    4.6         Taxes.......................................................7

5.  Development.............................................................7

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     5.1         Development Committee.......................................7
     5.2         Responsibilities of Development Committee...................7
     5.3         Meetings of the Development Committee.......................8
     5.4         Product Development Activities..............................8
     5.5         Funding of Product Development..............................9
     5.6         Publications...............................................10
6.  Copromotion.............................................................10
     6.1         Marketing Committee........................................10
     6.2         Responsibilities of Marketing Committee....................10
     6.3         Meetings of Marketing Committee............................11
     6.4         Joint Copromotion Activities...............................12
     6.5         Other Copromotion Activities...............................13
     6.6         Joint Copromotion Costs....................................14
     6.7         Shared Copromotion Expenses................................15
     6.8         Other Copromotion Matters..................................15
7.  Manufacturing and Supply................................................16
     7.1         Kos Responsibilities.......................................16
     7.2         Safety Surveillance Cost...................................17
     7.3         Cost of Manufacture........................................17
8.  Regulatory, Safety and Surveillance.....................................17
     8.1         Regulatory Matters.........................................17
     8.2         Adverse Events.............................................18
9.  Audit Rights............................................................18
10. Intellectual Property...................................................18
     10.1        Ownership of Intellectual Property.........................18
     10.2        Patent Prosecution.........................................19
     10.3        Notification of  Patent Litigation.........................19
     10.4        Patent Infringement........................................20
     10.5        Title to Trademarks........................................20
     10.6        Trademark License..........................................20
     10.7        Joint Marks................................................20
     10.8        Maintenance of Trademarks..................................20
     10.9        Notification of Trademark Litigation.......................21
     10.10       Trademark Infringement.....................................21
     10.11       Information and Settlements................................21
11. Confidentiality.........................................................21
     11.1        Disclosure of Know-How.....................................22
     11.2        Confidential Information...................................22
     11.3        Public Announcements.......................................22
12. Restrictive Covenants...................................................22
     12.1        Non-solicitation...........................................22
     12.2        Non-competition............................................23
13. Rights And Duties Upon Termination......................................23
     13.1        Payment Obligations........................................23

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     13.2        Continuing Obligations.....................................23
     13.3        Remedies...................................................24
14. Representations, Warranties and Indemnification.........................24
     14.1        Representations of Kos.....................................24
     14.2        Representations of DuPont..................................24
     14.3        Indemnification by Kos.....................................25
     14.4        Indemnification by DuPont..................................25
     14.5        Limitations on Indemnification.............................25
     14.6        Insurance..................................................26
15. Assignment..............................................................26
16. Notices.................................................................26
17. Miscellaneous...........................................................28
     17.1        Force Majeure..............................................28
     17.2        No Partnership or Joint Venture............................28
     17.3        Execution In Counterparts..................................28
     17.4        Governing Law..............................................28
     17.5        Waiver Of Breach...........................................28
     17.6        Severability...............................................29
     17.7        Entire Agreement...........................................29
18. Dispute Resolution......................................................29
     18.1        Internal Resolution........................................29
     18.2        Arbitration................................................29

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                  COPROMOTION AND FUTURE DEVELOPMENT AGREEMENT

         This Copromotion and Future Development Agreement (hereafter, the
"Agreement") is entered into as of the 3rd day of May, 2000, by and between Kos
Pharmaceuticals, Inc., a Florida corporation ("Kos"), and DuPont Pharmaceuticals
Company, a Delaware general partnership ("DuPont"), for the development and
marketing of Kos' fixed-dose combination niacin and lovastatin Product (as
defined below).

                                    Recitals

     A.     Kos is the owner of all right, title and interest in and to the
            Product and desires to copromote the Product and jointly plan other
            copromotion and future development activities for the Product with
            DuPont in the Territory (as defined below).

     B.     DuPont desires to copromote the Product and jointly plan other
            copromotion and future development activities for the Product with
            Kos in the Territory, and Kos is willing to grant DuPont such
            rights, all on the terms and subject to the conditions set forth in
            this Agreement.

     C.     Kos and DuPont desire to use their best efforts to work together to
            achieve the launch of the Product in the United States as quickly as
            possible, to aggressively promote the Product, and to optimize its
            sales. Kos and DuPont desire to jointly and equally detail the
            Product in the Territory.

     D.     Kos and DuPont shall on the date hereof enter into a Stock Purchase
            Agreement pursuant to which DuPont shall purchase an equity interest
            in Kos' common stock.

                                    Agreement

1.       Definitions

         1.1 Adverse Event(s) shall mean those events as defined by the FDA and
published in the U. S. Code of Federal Regulations, as amended from time to time
and published in the Federal Register.

         1.2 Affiliate shall mean any corporation, firm, partnership or other
entity that directly or indirectly owns, is owned by or is under common
ownership with a Party to the extent of at least fifty percent (50%) of the
equity or other ownership interest having the power to vote on or direct the
affairs of the entity and any

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person, firm, partnership, corporation or other entity actually controlled by,
controlling or under common control with a Party.

         1.3 Business Day shall mean a day on which commercial banks are open
for business in New York City. References in this Agreement to "days" other than
Business Days shall mean calendar days.

         1.4 Cost Of Distribution shall be ****************** of Net Sales.

         1.5 Cost Of Manufacture shall have the meaning set forth in Section
7.3.

         1.6 Development Committee shall mean the committee established and
conducted in accordance with the procedures set forth in Article 5.

         1.7 Effective Date shall mean the date upon which this Agreement is
effective and shall be the date this Agreement is entered into by both Parties.

         1.8 FDA shall mean the United States Food and Drug Administration and
any successor agency thereto and shall be deemed a reference to the Health
Protection Bureau for matters applicable to Canada.

         1.9 Joint Copromotion Activities shall have the meaning set forth in
Section 6.4.

         1.10 Joint Marks shall mean any trademark, service mark, copyright or
logo developed, applied for or registered or to be applied for or registered for
use in connection with educational activities or services, including "process of
care" materials or other jointly developed materials, not intended to be used
exclusively in association with the Product.

         1.11 Kos Trademark shall mean NicostatinTM, a trademark owned by Kos in
the Territory, and any other trademark, service mark or logo developed, applied
for, registered, or to be applied for or registered for use in connection with
the sale of the Product in the Territory, but shall not include Joint Marks.

         1.12 Know-How shall mean all present and future information developed
by Kos, whether or not in written form, that is not in the public domain and
that relates to the Product and shall include, without limitation, all
biological, chemical, pharmacological, toxicological, medical or clinical,
analytical, quality, manufacturing, research, or sales and marketing information
including all processes, methods, procedures, techniques, plans, programs, and
data and any other information relating to the Product or useful for the
development or commercialization of the Product in the Territory.

         1.13 Marketing Committee shall mean the committee established and
conducted in accordance with the procedures set forth in Article 6.

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         1.14 Minimum Product Details shall mean the minimum number of Product
Details to be performed by each Party as determined in accordance with Section
6.4.

         1.15 NDA shall mean a New Drug Application for the Product in
accordance with the requirements of the FDA.

         1.16 Net Operating Profit shall mean Net Sales of the Product in the
Territory minus: (i) Cost of Distribution, Safety Surveillance Cost and Cost of
Manufacture; (ii) royalties payable to Third Parties; (iii) an amount equal to
** of Net Sales to be retained by Kos; and (iv) Shared Copromotion Expenses if
not previously reimbursed under Section 6.7(c) (including expenses prior to
first commercial sale).

         1.17 Net Sales shall mean the gross receipts representing sales of the
Product in the Territory to Third Parties less the following deductions:

         (i)      if included in the aggregate gross invoice price of the
                  Product, sales and excise taxes, duties, and any other
                  governmental charges imposed upon the production, importation,
                  use or sale of such Product;

         (ii)     trade, quantity and cash discounts allowed on the Product;

         (iii)    allowances or credits to customers on account of rejection or
                  return of the Product or on account of price reductions
                  affecting such Product;

         (iv)     Product rebates and Product charge-backs including those
                  granted to managed care entities and pharmaceutical benefit
                  management service entities; and

         (v)      provisions for actual or expected write-offs of uncollectible
                  customer accounts for previously recorded sales or other
                  reserves or provisions established consistent with U.S.
                  Generally Accepted Accounting Principles ("GAAP").

         1.18 Other Copromotion Activities shall have the meaning set forth in
Section 6.5.

         1.19 Party(ies) shall mean each of Kos and DuPont.

         1.20 Patents shall mean all patents and patent applications in the
Territory that are or become owned by Kos, or to which Kos otherwise has, now or
in the future, the right to grant licenses and license rights or sublicense and
sublicense rights, that generically or specifically cover the Product or a use
or formulation of the Product. Included within the definition of Patents are all
continuations, continuations-in-part, division, patents of addition, reissues,
renewals or extensions thereof. Also included within the definition of Patents
are any patents or patent

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applications that generically or specifically claim any improvements on the
Product that are developed by Kos, or which Kos otherwise has the right to grant
licenses and license rights or sublicense and sublicense rights, now or in the
future, during the term of this Agreement. The current list of patent
applications and patents encompassed within Patents is set forth in Appendix A
attached hereto. Appendix A shall be updated by Kos at least annually during the
term of this Agreement, but the inadvertent failure to include an item on such
updates of Appendix A does not disqualify such item as a Patent under this
definition.

         1.21 Product shall mean all strengths and dosage forms of Kos'
fixed-dose extended release niacin and lovastatin combination product, that is
the subject of Investigational New Drug application number 56,027 effective from
June 26, 1998, or its successor applications, for all indications approved by
the FDA at any time during the Term.

         1.22 Product Detail(s) shall mean a face-to-face meeting, in an
individual or group practice or hospital setting, between (i) a professional
representative of the applicable Party, meeting the professional standards for
such representatives that are established by the Marketing Committee, and (ii) a
health care professional with prescribing authority, which health care
professional has been designated by the Marketing Committee as a member of the
target calling audience, during which a full presentation of the Product
attributes are orally presented. The presentation of the Product during any
Product Detail must be one of the *** presentations on which the most time is
spent during such meeting, for the period of time determined by the Marketing
Committee. When used as a verb, "Product Detail" shall mean to engage in a
Product Detail.

         1.23 Product Development Costs shall mean those out-of-pocket costs
approved by the Development Committee incurred in connection with Product
Development Activities defined in Section 5.4. Product Development Costs do not
include any expenditures for studies commenced prior to the approval of the NDA
unless specifically approved by DuPont. The amounts and reimbursement of Product
Development Costs shall be determined in accordance with Sections 5.4 and 5.5.

         1.24 Safety Surveillance Cost shall have the meaning set forth in
Section 7.2.

         1.25 Shared Copromotion Expenses shall mean all expenses approved by
the Marketing Committee directly related to the selling, marketing or promotion
of the Product in the Territory for Other Copromotion Activities. Shared
Copromotion Expenses do not include each Party's costs for Joint Copromotion
Activities. The specific components and amounts of Shared Copromotion Expenses
shall be determined in accordance with Section 6.7.

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         1.25 Six-Month Period shall mean each period from January through June
and July through December of each Year.

         1.26 Term shall have the meaning set forth in Section 3.1.

         1.27 Territory shall mean the United States of America, its territories
and possessions, including Puerto Rico, and Canada.

         1.28 Third Party(ies) shall mean any person or entity other than Kos
and DuPont or their Affiliates.

         1.29 Year shall mean each twelve month period ending December 31 during
the Term.

2.       Grant of Rights

         Kos grants to DuPont the exclusive license right, to the extent of Kos'
rights and interests under the Patents and Know-How, to co-develop and copromote
the sale of the Product in the Territory, subject to Kos' right to co-develop
and copromote the Product in the Territory and all the other terms and
conditions of this Agreement. Kos shall retain all of its rights with respect to
the Product outside the Territory.

         DuPont shall have the opportunity to negotiate for license rights to
the Product in ****** prior to *************************************************
******************************. In each case in which Kos is contemplating
granting any license rights to the Product in ****** prior to such date, once
Kos decides to pursue granting such rights or begins negotiations with a Third
Party regarding such rights, Kos shall not grant any such rights for a period of
90 days, during which 90-day period DuPont is given an opportunity to negotiate
for such rights that is at least equal to the opportunity given to any other
Third Party.

3.       Term, Termination and Renegotiation

         3.1 Term. This Agreement shall have an Initial Term of ten (10) years
beginning on the Effective Date, unless earlier terminated pursuant to Section
3.2 (the "Initial Term"). After the Initial Term, this Agreement shall
automatically renew for one (1) year renewal terms unless it is terminated by
either Party at least sixty (60) days before the end of the then current term
(the "Initial Term" and the renewal terms are collectively referred to as the
"Term").

         3.2 Early Termination. Each Party shall have the right to terminate
this Agreement before the end of the Term (i) upon a material breach of this
Agreement by the other Party where such breach is not cured within ninety (90)
days following the other Party's receipt of written notice of such breach; (ii)
if the FDA withdraws marketing approval for the Product; (iii) upon the
bankruptcy or insolvency, or the

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making or seeking to make or arrange an assignment for the benefit of creditors
of the other Party, or the initiation of proceedings in voluntary or involuntary
bankruptcy, or the appointment of a receiver or trustee of such Party's property
that is not discharged within ninety (90) days; (iv) if at least one patent
based on either of the patent applications U.S. Serial Numbers 08/368,378 and
08/814,974 has not issued within sixty (60) days of the Effective Date; (v) if a
U.S. patent based upon U.S. Serial Numbers 08/368,378 or 08/814,974, or based
upon another U.S. application not yet filed by Kos, and having a claim covering
the Product is declared invalid by a court of competent jurisdiction, is
dedicated to the public by Kos prior to its expiration or is otherwise
unenforceable and there are no remaining claims covering the Product in an
issued U.S. patent owned by Kos; or (vi) if the approval of the NDA for the
Product is delayed by more than 24 months from the date of submission of the
NDA.

         3.3 Renegotiation. In the event that (i) the indication in the approved
NDA is substantially narrower than that approved for Kos' Niaspan(R) product, or
(ii) a generic version of niacin plus lovastatin is approved by the FDA, then
the Parties shall promptly negotiate in good faith revisions with respect to the
Parties' obligations for Product Development Costs and Copromotion Activities
and the Term of the Agreement.

4.       Fees and Payments

         4.1 Stock Purchase Agreement. Contemporaneously with the execution of
this Agreement, the Parties shall execute a Stock Purchase Agreement pursuant to
which DuPont shall purchase an equity interest in Kos' common stock on the terms
set forth therein.

         4.2 Fees. In consideration for the co-development and copromotion
rights under the Patents and Know-How granted to DuPont in this Agreement,
DuPont shall pay a milestone payment of $17,500,000 to Kos upon Kos receiving
marketing clearance from the FDA for the Product. Such milestone payment shall
be due within 10 Business Days following the occurrence of the milestone.

         4.3 Reimbursements. The foregoing milestone payment shall be in
addition to the reimbursement payments DuPont is required to make pursuant to
Sections 5.5 and 6.7 and any other payments DuPont is required to make under
this Agreement.

         4.4 Product Profits. Subject to the provisions of Section 6.6, Kos and
DuPont shall each be entitled to receive 50% of the Net Operating Profit, or be
obligated to bear 50% of the Net Operating Profit in the event such amount is a
loss, for each quarter. The Net Operating Profit shall be calculated by Kos and
communicated to DuPont in writing within 45 days following the end of each
calendar quarter, except following the fourth calendar quarter, in which case
such

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calculation shall be communicated within 60 days following the end of the
quarter. Kos shall pay to DuPont 50% of the Net Operating Profit within 10
Business Days following such written communication; in the event that such Net
Operating Profit amount is a loss, DuPont shall pay to Kos within 10 Business
Days following such written communication 50% of the amount of the loss.

         4.5 Payments. All payments under this Agreement shall be in U.S.
dollars in immediately available funds, and, unless instructed otherwise by the
receiving Party, shall be made via wire transfer to the account designated from
time to time by the receiving Party.

         4.6 Taxes. Unless otherwise required by law, each Party shall be
responsible for paying and reporting all of its own taxes and fees, including
without limitation income taxes, payroll taxes, franchise taxes and all taxes
and fees in connection with the Party conducting business in any jurisdiction.

5.       Development

         5.1 Development Committee. Within thirty (30) days following the
Effective Date, the Parties shall form a Development Committee whose
responsibility shall be to direct the regulatory and clinical development of the
Product other than in connection with the NDA approval for the United States.
The Development Committee shall have equal representation from Kos and DuPont
and shall have a chairperson designated by Kos and a vice-chairperson designated
by DuPont. The Development Committee may from time to time include additional
non-voting ad-hoc representatives from either Party on specific issues as the
need arises. As appropriate, the Development Committee may establish one or more
sub-committees to act on matters that may arise between meetings of the
Development Committee or to consider matters that would be more effectively
considered by a smaller committee.

         Each member of the Development Committee shall have one vote on all
matters, and whenever action is to be taken by vote of the Development
Committee, it shall be authorized by a majority vote and shall be binding on
both Parties. Any matters of the Committee that result in a tie vote that the
chairperson and vice-chairperson are unable to resolve shall be referred to the
dispute resolution provisions set forth in Article 18.

         5.2 Responsibilities of Development Committee. The Development
Committee shall be responsible for the planning and oversight of all preclinical
and clinical activities associated with the Product (except for studies required
prior to NDA approval in the United States), for all post-approval regulatory
matters concerning the Product, and for managing Product Development Costs. Such
planning and oversight responsibilities shall include, without limitation, the
following: (i) study protocol design, preparation and approval; (ii) the
selection and

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recruitment of clinical sites and investigators; (iii) quality assurance and
auditing with respect to the conduct of studies; (iv) laboratory analysis of
study samples and specimens; (v) analysis of study data; (vi) safety monitoring
and reporting; (vii) preparation of study reports; (viii) regulatory reports;
(ix) post-approval meetings and other dialogue with the FDA; (x) medical and
scientific support for copromotion activities as requested by the Marketing
Committee; (xi) the establishment of timetables and cost budgets for all studies
and development activities associated with the Product and monitoring actual
performance; (xii) the creation of the draft initial Product development plan by
the end of the second quarter after the Effective Date; and (xiii) approval of
safety and surveillance and drug information efforts. DuPont's representatives
on the Development Committee shall be kept informed of pre-approval Product
development activities and shall be entitled to have a representative attend
meetings with the FDA.

         5.3 Meetings of the Development Committee. The first meeting of the
Development Committee shall occur within thirty (30) days after the Effective
Date. Thereafter, meetings shall be held once per calendar quarter unless no
later than thirty (30) days in advance of any meeting there is a determination,
by agreement of both Parties, that no new business or other activity has
transpired since the previous meeting, and that there is no need for a meeting.
In such instance, the next quarterly meeting will be scheduled. The Development
Committee shall also establish a procedure, agreeable to both Parties, for
either (i) calling special interim meetings of the Development Committee in the
event of the need for Development Committee decisions between regularly
scheduled meetings or (ii) establishing a process for making such interim
decisions.

         The location of such meetings shall alternate between Kos' offices in
the Miami, Florida metropolitan area and DuPont's offices in the Wilmington,
Delaware metropolitan area unless otherwise agreed upon between the Parties.
Development Committee meetings may, upon the agreement of both Parties, be via
teleconference and/or videoconference.

         Minutes of each Development Committee meeting shall be transcribed and
issued by a designee of the Committee within thirty (30) days after each meeting
and shall be approved by the chairperson and vice-chairperson no later than the
first order of business at the immediately succeeding Development Committee
meeting. Each Party shall bear their own expenses in connection with attending
meetings of the Development Committee.

         5.4 Product Development Activities. Subject to the direction of the
Development Committee, Kos shall be fully responsible for performing, or causing
to be performed, all development activities associated with the Product in the
Territory in compliance with "current Good Clinical Practices" and "current Good
Manufacturing Practices" as set forth by the FDA and otherwise in conformity
with all applicable local, state, and Federal laws and regulations. The Parties
agree

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that, subject to the approval of the Development Committee, in executing its
responsibilities hereunder, Kos may rely on services performed by qualified
Third Party providers of such services or Kos may purchase services from DuPont.
Each Party agrees to spend at least $************ on such Product development
activities ("Product Development Activities") during the Term as agreed by the
Development Committee, unless Kos agrees to a lesser level of expenditures. Such
$************ amount to be spent by DuPont shall be paid by DuPont in accordance
with its 50% reimbursement obligations as set forth in Section 5.5. Such Product
Development Activities shall be limited to the following and may not be expanded
without the consent of both Kos and DuPont:

         a. Regulatory Requirements: All preclinical or clinical activities
            required for regulatory approval of the Product in Canada, and
            studies or other development activities that may be required after
            the approval of the NDA by the FDA, including without limitation,
            all preclinical or clinical studies required for safety, efficacy,
            quality, or manufacturing purposes.

         b. Phase IV Marketing Studies: To the extent requested by the Marketing
            Committee and approved by the Development Committee, all preclinical
            or clinical studies conducted for marketing purposes, including
            without limitation a long-term clinical outcome study.

         c. Studies for Additional Indications or Labeling: To the extent
            approved by both the Development Committee and the Marketing
            Committee, all preclinical or clinical studies to support regulatory
            approval in the Territory for new or modified treatment indications,
            new dosage forms, new strengths or other enhancements for the
            Product.

         5.5 Funding of Product Development. Kos shall be responsible for all
costs incurred in connection with the preclinical and clinical development of
the Product up to and including NDA submission, review and approval. DuPont
shall be responsible for providing funding for 50% of Product Development Costs;
provided, however, that neither DuPont nor Kos are obligated to agree to conduct
Product Development Activities that in the aggregate would create Product
Development Costs in excess of $********** during the Term. DuPont shall
reimburse Kos for 50% of all Product Development Costs incurred by Kos for
studies that commence after the date Kos receives marketing clearance from the
FDA for the Product. Such costs shall be paid within 10 Business Days of
DuPont's receipt of an invoice for such costs, which shall be delivered by Kos
within 45 days following the end of each calendar quarter, except for the fourth
calendar quarter, in which case such invoice shall be delivered within 90 days
following the end of the quarter. Each invoice shall indicate expenditures
incurred classified by categories (a), (b) and (c) in Section 5.4.
Notwithstanding the foregoing, Kos may deliver invoices to DuPont at any time
that the aggregate amount of Product Development Costs for which Kos

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shall be entitled to seek 50% reimbursement from DuPont exceeds $********** and
DuPont shall reimburse Kos for such costs within 10 Business Days of DuPont's
receipt of such invoices. Kos will use its best efforts to provide DuPont with
at least 15 days advance notice of such invoices.

         5.6 Publications. The Development Committee, with input from the
Marketing Committee, shall have oversight responsibility for the publication by
either Party or their representatives of any scientific, medical, or technical
article or other publication relating to the Product. Such responsibility shall
include approval of content, manuscript, preparation, authorship and choice of
journal(s) to which such submission is intended as well as, to the extent
feasible, final pre-publication approval.

6.       Copromotion

         6.1 Marketing Committee. Within thirty (30) days after the Effective
Date, Kos and DuPont shall assemble a team of appropriate personnel from both
Kos and DuPont (the "Marketing Committee") to plan the pre-launch, launch, and
ongoing sales and promotional strategies and to review and direct such
activities for the Product in the Territory. The Marketing Committee shall have
equal representation from Kos and DuPont and shall have a chairperson designated
by Kos and a vice-chairperson designated by DuPont. The Marketing Committee may
from time to time include additional non-voting ad-hoc representatives from
either Party on specific issues as the need arises. As appropriate, the
Marketing Committee may establish one or more sub-committees to act on matters
that may arise between meetings of the Marketing Committee or to consider
matters that would be more effectively considered by a smaller committee.

         Each member of the Marketing Committee shall have one vote on all
matters, and whenever action is to be taken by vote of the Marketing Committee,
it shall be authorized by a majority vote and shall be binding on both Parties.
Any matters of the Committee that result in a tie vote that the chairperson and
vice-chairpersons are unable to resolve shall be referred to the dispute
resolution provisions set forth in Article 18.

         6.2 Responsibilities of Marketing Committee. The Marketing Committee
shall have planning, oversight, performance evaluation and decision-making
authority and responsibility for all sales, marketing and promotional activities
related to the Product and to the field sales forces of both Parties in the
Territory, except that the Marketing Committee shall have no direct authority
over the employees of either Party. The Committee's responsibilities shall
include, without limitation, the following activities: (i) develop, and modify
as appropriate, the fundamental marketing and promotion strategies; (ii) develop
a comprehensive annual marketing plan, calendarized by quarter; (iii) establish
and implement appropriate sales and marketing policies, programs, and
procedures; (iv) establish

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targeted physician calling universe and corresponding reach and frequency call
plans; (v) establish the professional criteria for field sales representatives;
(vi) establish minimum Product Details by calendar quarter; (vii) develop
complementary strategies, policies, and objectives for managed care and
professional services representatives; (viii) oversee the preparation of
comprehensive annual business plans for the Product; (ix) develop and monitor
individual and area performance measures for all field sales activities; (x)
consult with Kos on pricing and discount strategies; (xi) establish and monitor
Product sampling practices; (xii) forecast annual and quarterly prescriptions
and sales and set appropriate production requirements for sales and samples;
(xiii) establish requirements for and regularly review prescription tracking,
call reporting, and other secondary market data; (xiv) develop and review all
marketing and promotional material such as Product Detail aids, advertising,
promotional give-aways, speaker kits, and direct mail; (xv) establish as
appropriate supplementary non-personnel promotional programs such as compliance,
telemarketing and internet activities; (xvi) develop and direct
professional/medical education programs including seminars, symposia,
participation at professional and medical conferences, and conventions,
physician advocacy programs, and event marketing programs; (xvii) plan and
coordinate all Product public relations activities; (xviii) plan and implement
appropriate training programs; (xix) plan and implement primary market research
activities; (xx) develop trademarks and packaging materials; and (xxi) determine
cost budgets for all activities and monitor actual performance. Notwithstanding
clauses (x) and (xiv) above, Kos shall bear final responsibility for determining
pricing for the Product and for ensuring that Product promotional materials
comply with the Federal Food, Drug and Cosmetic Act and all other applicable
laws and regulations, and for all costs associated with such compliance. Kos has
previously provided DuPont a copy of its standard operating procedure for
medical/regulatory/legal review of promotional materials.

         6.3 Meetings of Marketing Committee. Meetings of the Marketing
Committee shall be held quarterly commencing with the first quarter following
the Effective Date and until the filing of the NDA with the FDA, and shall be
held more often thereafter as determined by the Marketing Committee. The
location of Marketing Committee meetings and whether to hold them via
teleconference and/or videoconference shall be determined by the Marketing
Committee. Minutes of each Marketing Committee meeting shall be transcribed and
issued by a designee of the Committee within ten (10) Business Days after each
meeting and shall be approved by the chairperson and vice-chairperson not later
than the first order of business at the immediately succeeding Marketing
Committee meeting. Each Party shall bear its own expenses in connection with
attending meetings of the Marketing Committee. The Committee shall also
establish a procedure, agreeable to both Parties, for either (i) calling special
interim meetings of the Committee in the event a need for Committee decisions
arises between regularly scheduled meetings or (ii) establishing a process for
making such interim decisions.

                                       11
<PAGE>

         6.4 Joint Copromotion Activities. Subject to the direction of the
Marketing Committee, each of Kos and DuPont shall be responsible for performing
the following copromotion activities (the "Joint Copromotion Activities"), in
each case in accordance with the minimum activity levels established by the
Marketing Committee. It is the intent of the Parties that the minimum activity
levels established by the Marketing Committee for the categories of activities
described in clauses a. through d. below be the same for each party, and that no
amount of activity in any one such category may be substituted for or deemed
equivalent to activity in another such category.

            a. Field Sales: The Marketing Committee shall determine the target
               audience and the monthly call reach and frequency objectives for
               both sales organizations as appropriate. Each of Kos and DuPont
               commits to performing Minimum Product Details during each
               Six-Month Period during the Term, which shall not be less than
               ******* Product Details during each of the first six Six-Month
               Periods following the commencement of commercial sale of the
               Product in the Territory. Each Party shall maintain records of
               each Detail by its sales force using a call document which
               records the name and address of the member of the target
               audience, the date and position of the Detail and the number of
               samples delivered and shall supply a monthly record of the number
               of total Details to the other Party within 60 days of the end of
               each month in a form to be established by the Marketing
               Committee. The Marketing Committee shall determine the level and
               extent of hospital activities, including obtaining hospital
               formulary approval, conducting in-services and performing Product
               Details, and shall determine the equalization of activity between
               the Kos and DuPont sales forces given that DuPont is likely to
               conduct a greater amount of hospital activities. The Marketing
               Committee shall adjust the number of Product Details after the
               first 12 months as appropriate to optimize sales opportunities
               for the Product.

            b. Sampling: The Marketing Committee shall determine the level of
               sampling per member of the target audience. All sample
               distribution, reporting and storage shall be conducted by each
               Party in accordance with the Prescription Drug Marketing Act.

            c. Other Field Activities: The Marketing Committee shall determine
               the minimum level of effort each Party is required to commit to
               the field activities listed on Appendix B attached hereto,
               including without limitation managed care, professional services,
               clinical liason, CoumaCare and hospital based activities. The
               minimum amount of effort and

                                       12
<PAGE>

               resources that each Party is directed by the Marketing Committee
               to commit to each of the activities listed on Appendix B may be
               different, provided that the minimum overall effort and resources
               that each Party is directed to commit to all of such activities
               is determined by the Marketing Committee to be substantially
               equivalent.

            d. On-Going Sales Force Training: Each of Kos and DuPont agrees to
               provide periodic on-going training on the Product to their
               respective sales forces in accordance with training schedules and
               materials established by the Marketing Committee.

         6.5 Other Copromotion Activities. Other than the Joint Copromotion
Activities set forth in Section 6.4 and subject to the direction of the
Marketing Committee, Kos shall be fully responsible for performing, or causing
to be performed, all other copromotion activities relating to the Product in the
Territory (the "Other Copromotion Activities"). The Parties agree that, subject
to the approval of the Marketing Committee, in executing its responsibilities
hereunder, Kos may rely on services performed by qualified Third Party providers
of such services or Kos may purchase services from DuPont. Other Copromotion
Activities may include, without limitation, the following:

            a. Advertising, marketing and promotion materials including sales
               aids, give-aways, direct mail, speaker kits, etc.

            b. Samples

            c. Public Relations

            d. Medical education and physician advocacy programs, including
               event marketing meetings, medical symposia, and physician
               advocacy programs, medical meetings and conventions.

            e. Publications including scientific presentations, reprints, and
               supplements.

            f. Honoraria and educational grants.

            g. Persistency and compliance programs.

            h. Telemarketing programs.

            i. Training in connection with the launch of the Product, consisting
               principally of (i) preparing and distributing all training
               materials related to the Product; (ii) training the personnel at
               Kos and DuPont who shall be responsible for on-going training for
               each Party; (iii) organizing and conducting, with appropriate
               assistance from DuPont, all training activities involving the
               combined Product sales forces of the Parties or large segments
               thereof.

                                       13
<PAGE>

            j. Primary market research.

            k. Other activities as directed by the Marketing Committee.

         6.6 Joint Copromotion Costs.

             (a) Resources. It is the intent of Kos and DuPont that they will
devote equal resources to carry-out the Joint Copromotion Activities.
Accordingly, except as provided in this Section 6.6, each Party shall fully
bear, without recourse to the other Party, all of the costs incurred by such
Party in connection with such Party's performance of the Joint Copromotion
Activities.

             (b) Measurement of Joint Copromotion Activities. The methods for
measuring the actual number of Product Details and other Joint Copromotion
Activities shall be agreed upon by both Parties prior to the launch of the
Product in the Territory. Following the end of each Six-Month Period, the
Marketing Committee shall review the Joint Copromotion Activities, including
without limitation the number of Product Details performed by each Party during
the preceding Six-Month Period. The actual number of Product Details performed
by a Party during a Six-Month Period shall be expressed as a percentage of the
number of Minimum Product Details established for such period by the Marketing
Committee.

             (c) Six-Month Period Shortfalls by One Party. At the end of each
Six-Month Period, in the event that a Party (but only one Party) performed fewer
than 95% of the Minimum Product Details during that Six-Month Period, the
portion of the Net Operating Profit to which such Party would be otherwise
entitled for that Six-Month Period under Section 4.4 shall be adjusted such that
the payment received by such Party for the Six-Month Period is reduced (or
increased in the event such Net Operating Profit is a loss) by a percentage
equal to the percentage difference between the required number of Minimum
Product Details during such Six-Month Period and the actual number of Product
Details performed by such Party during such period. For example, if the Minimum
Product Details for a Six-Month Period is ******* and a Party actually performs
******* Product Details during such period (i.e. 85% of the Minimum Product
Details), such Party would be entitled to receive 35% [i.e., 50% - 15%] (or, in
the event of a loss, would be required to pay 65%) of the Net Operating Profit
during such Six-Month Period.

             (d) Six-Month Period Shortfalls by Both Parties. In the event that
both Parties perform fewer than 95% of the Minimum Product Details during the
same Six-Month Period, the Net Operating Profit for such period shall be divided
between the Parties pro rata based on the actual number of Product Details
performed by each Party during such period.

             (e) Adjustments to Net Operating Profit. Subject to clauses (c) and
(d) above, within 60 days of the end of each Six-Month Period, Kos shall invoice

                                       14
<PAGE>

DuPont for the adjustment (positive or negative), and Kos or DuPont, as
applicable, shall pay the other within 10 Business Days.

         6.7 Shared Copromotion Expenses.

             (a) Costs. All costs directly incurred by Kos in order to perform,
or cause to be performed, such Other Copromotion Activities as are approved by
the Marketing Committee shall constitute Shared Copromotion Expenses. Such costs
shall exclude mark-ups over actual direct costs and allocations of overhead;
provided, however, that (i) such costs may include, if approved by the Marketing
Committee, the costs of directly required incremental Kos personnel below the
level of Office Director, and (ii) the cost of samples shall be included at
their Cost of Manufacture but shall not include each Party's respective cost of
distributing samples to their own sales force.

             (b) Budgets. At least 90 days prior to each Year, the Marketing
Committee shall establish an annual budget for the Shared Copromotion Expenses
for such year, calendarized by quarter, and shall regularly review actual cost
performance compared with the budget. Prior to commencing any new activity not
provided for in the budget, the Marketing Committee will also approve a cost
budget for such activity. Kos shall not incur any Shared Copromotion Expense
that has not been included in the annual budget, approved by the Marketing
Committee in advance, or otherwise specifically authorized by the Marketing
Committee.

             (c) Funding of Shared Copromotion Expenses. Kos shall be
responsible for directly funding all Shared Copromotion Expenses.
Notwithstanding the foregoing sentence, Kos may deliver invoices to DuPont at
any time that the aggregate amount of Shared Copromotion Expenses for which Kos
shall be entitled to seek 50% reimbursement from DuPont exceeds $********** and
DuPont shall reimburse Kos for such costs with 10 Business Days of DuPont's
receipt of such invoices. Kos will use its best efforts to provide DuPont with
at least 15 days advance notice of such invoices.

         6.8 Other Copromotion Matters.

             (a) Booking of Sales Revenue. Kos shall record on its books all
revenue from gross and Net Sales of the Product.

             (b) Packaging. The Marketing Committee shall have the
responsibility for approving all packaging materials subject to input from the
Development Committee with respect to regulatory requirements and from Kos
manufacturing with respect to shipping and cost considerations. Subject to the
approval of the Marketing Committee with respect to size, positioning and other
relevant matters, Kos and DuPont shall both be entitled to have their corporate
logos appropriately displayed on Product packages.

                                       15
<PAGE>

             (c) Promotional Materials. Subject to the approval of the Marketing
Committee with respect to size, positioning and other relevant matters, Kos and
DuPont shall both be entitled to have their corporate logos appropriately
displayed on Product promotional materials.

             (d) Trademarks. The Marketing Committee shall approve the names,
design, and usage in the Territory of all new Kos Trademarks associated with the
Product; provided that if the Marketing Committee is unable to agree on matters
involving the Kos Trademarks, Kos shall have the authority to resolve such
disputes.

             (e) Field Sales Representatives. Except with the prior written
consent of both Parties, all field sales representatives who are responsible for
Product Details shall be full-time employees of the respective Parties. However,
without Kos' consent, DuPont shall have the right to contract with McKesson
HBOC, Inc. or its successor to employ a contract sales force to fulfill part of
DuPont's obligations for Product Details, provided that such contract sales
force is dedicated exclusively to DuPont and receives training and compensation
comparable to sales representatives of Kos and DuPont, and further provided that
such sales representatives meet the professional standards for such
representatives that are established by the Marketing Committee.

             (f) Sales Incentive Plan. DuPont shall implement and maintain an
incentive plan for the Product for its sales force that is consistent with its
overall sales incentive compensation plan for its own products.

7.       Manufacturing and Supply

         7.1 Kos Responsibilities. Kos shall use its commercially reasonable
best efforts to produce and timely supply the Product and Product samples for
the Territory. Kos shall manufacture, package, store and ship the Product and
Product samples in strict adherence to "current Good Manufacturing Practices" as
set forth by the FDA, consistent with the Product's approved NDA and the Quality
Agreement (to be negotiated by the Parties within 60 days of the Effective Date
and then attached hereto as Appendix D), and otherwise in conformity with all
applicable local, state, and Federal laws and regulations. Kos shall also use
its commercially reasonable best efforts to produce the Product at the highest
appropriate quality standards and at the least cost feasible. Kos shall supply
such Product and Product samples based on reasonable advance notification of
Product and Product sample requirements as forecasted by the Marketing
Committee, and Kos shall be responsible for providing capacity to support future
requirements for the Product and Product samples as determined by the Marketing
Committee.

         7.2 Safety Surveillance Cost. Safety Surveillance Cost shall mean Kos'
costs directly attributable to the Product, if any, for personnel and related
costs for

                                       16
<PAGE>

handling safety surveillance and customer inquiries; provided however, that such
costs shall not exceed the equivalent of four full time personnel without the
approval of DuPont.

         7.3 Cost of Manufacture. Cost of Manufacture shall be Kos' actual fully
allocated manufacturing cost directly related to the Product calculated in
accordance with GAAP, and determined consistent with Kos' cost accounting method
as set forth by example in Appendix C, and consistent with "cost of sales" as
disclosed in Kos' public financial statements for the respective period, plus a
mark-up of ***************** on such costs; provided that such mark-up shall not
be charged on the cost of lovastatin in excess of $***** per kilogram. DuPont
reserves the right to audit Kos' Cost of Manufacture twice per Year. In the
event Kos requires services from Third Party providers for manufacture or
distribution of the Product, Kos shall first offer DuPont the option to provide
such services.

8.       Regulatory, Safety and Surveillance

         8.1 Regulatory Matters.

             (a) Permits. Kos shall maintain all regulatory and governmental
permits, licenses and approvals that may be necessary to manufacture, ship, sell
and market the Product in the Territory.

             (b) Reporting. Kos shall be responsible for any reporting of
matters regarding the manufacture and sale of the Product, including Adverse
Events, to the FDA and other relevant regulatory authorities, in accordance with
applicable laws and regulations. Kos shall immediately notify DuPont of any such
matter and promptly furnish complete copies of such reports to DuPont. In the
event Kos or DuPont should become aware of information that may require a
recall, field alert, Product withdrawal or field correction arising from any
defect in the Product, it shall immediately notify the other Party in writing.

         8.2 Adverse Events. Promptly after the Effective Date, in recognition
of Kos' primary responsibility for reporting Adverse Events associated with the
Product, the Parties shall agree upon standard operating procedures for the
investigation and reporting of Adverse Events regarding the Product. The Parties
shall immediately implement such agreed procedures and shall provide each other
on a regular basis with any appropriate information that enables the other Party
to meet its regulatory obligations in the Territory with respect to the Product
or that is relevant to the safe use of the Product. The agreed procedures will
be reviewed jointly on a regular basis or when there is a change in regulations
governing Adverse Event reporting.

                                       17
<PAGE>

9.       Audit Rights

         Each of Kos and DuPont shall keep complete and accurate records of
their respective Product Details, incentive compensation payments for the
Product to sales representatives, and Kos shall keep complete and accurate
records of the Net Operating Profit and reimbursable expenses. Each Party shall
have the right, at such Party's expense, through a certified public accountant
or like person reasonably acceptable to the other Party, upon execution of a
confidentiality agreement, to examine such records during regular business hours
upon reasonable notice during the life of this Agreement and for six (6) months
after its termination; provided, however, that (i) such examination shall not
take place more often than once a Year and shall not cover such records for more
than the preceding Year, and (ii) such accountant shall report to such Party
only as to the accuracy of the reports or payments provided or made by the other
Party under this Agreement. Any adjustments required as a result of overpayments
or underpayments identified through a Party's exercise of audit rights, and any
other adjustments that may be required from time to time in order to correct
overpayments or underpayments under this Agreement, shall be made by subtracting
or adding, as appropriate, amounts from or to the next distribution of Net
Operating Profit in accordance with Section 4.4. The Party requesting the audit
shall bear the full cost of the audit unless such audit correctly discloses that
the discrepancy for the Year differs by more five percent (5%) from the amount
the accountant determines is correct, in such case the owing Party shall pay the
reasonable fees and expenses charged by the accountant. In the event that a
Party disputes an invoice or other payment obligation under this Agreement, such
Party shall timely pay the amount of the invoice or other payment obligation,
and the Parties shall resolve such dispute in accordance with Article 18.

10.      Intellectual Property

         10.1 Ownership of Intellectual Property. Kos shall have and retain sole
and exclusive right, title and interest in and to all inventions, discoveries,
writings, trade secrets, know-how, methods, practices, procedures, engineering
information, designs, devices, improvements, manufacturing information and other
technology, whether or not patentable or copyrightable, and any patent
applications, patents, or copyrights based thereon ("Inventions") that are made,
discovered, conceived, reduced to practice or generated by Kos (or its employees
or representatives) or jointly by Kos and DuPont (or their employees or
representatives) that in any way relate to the Product or the active ingredients
(niacin and lovastatin) in the Product. DuPont shall own exclusively all
Inventions made by DuPont (or its employees or representatives) that in any way
relate to the Product or the active ingredients in the Product. With respect to
any Inventions not relating in any way to the Product or the active ingredients
in the Product, each Party shall own all right, title and interest in and to all
such Inventions made, discovered, conceived, reduced to practice or generated
solely by such Party (or its employees or representatives), and the Parties
shall jointly own the right, title and interest in and to all such Inventions
made, discovered, conceived, reduced to practice or generated jointly by the
Parties (or their employees or

                                       18
<PAGE>

representatives). The Parties agree to cooperate in the filing of patent
applications upon such jointly-owned inventions. With respect to Inventions made
by DuPont that in any way relate to the Product or the active ingredients in the
Product, DuPont shall grant Kos a fully-paid, perpetual, exclusive license to
make, use or sell such Inventions, without limiting in any way DuPont's rights
with respect to the use of such Inventions. With respect to Inventions made
jointly by the Parties that in any way relate to the Product or the active
ingredients in the Product, Kos shall grant DuPont a fully-paid, perpetual,
exclusive license to make, use or sell such Inventions, without limiting in any
way Kos' rights with respect to the use of such Inventions.

         10.2 Patent Prosecution. Kos, at its expense, shall have responsibility
for filing, prosecution and maintenance of all Patents that it owns in the
Territory. Kos shall disclose to DuPont the complete texts of all Patents filed
by Kos in the Territory that relate to the Product as well as all information
received concerning the institution or possible institution of any interference,
opposition, re-examination, reissue, revocation, nullification or any official
proceeding involving a Patent anywhere in the Territory. Kos shall agree to keep
DuPont promptly and fully informed of the course of patent prosecution or other
proceedings including by providing DuPont with copies of substantive
communications, search reports and Third Party observations submitted to or
received from patent offices throughout the Territory. DuPont shall, if
requested by Kos, provide appropriate patent consultation to Kos. DuPont shall
hold all information disclosed to it under this Section as confidential subject
to the provisions of Section 11.2.

         10.3 Notification of Patent Litigation. In the event of the institution
of any suit by a Third Party against Kos or DuPont for patent infringement
involving the manufacture, use, sale, license or marketing of the Product
anywhere in the Territory, the Party sued shall promptly notify the other Party
in writing.

         10.4 Patent Infringement. In the event that Kos or DuPont becomes aware
of actual or threatened infringement of a Patent anywhere in the Territory, that
Party shall promptly notify the other Party in writing. Kos shall have the sole
right, but not the obligation, to investigate and/or bring an infringement
action against any Third Party. Kos shall have full control over the conduct of
such investigations and litigation, including the settlement thereof. The cost
of such investigation and litigation shall be borne entirely by Kos, with Kos
being entitled to the entire proceeds, if any, of such litigation, unless DuPont
agrees, at its sole discretion, within 20 days of such notice, to bear an equal
share of such cost, in which case it shall also be entitled to an equal share of
any proceeds of such litigation. DuPont shall reasonably assist Kos and
cooperate in any such investigation and litigation at Kos' request and at Kos'
expense, unless DuPont has otherwise agreed to

                                       19
<PAGE>

participate in the litigation. Should Kos choose not to bring an infringement
action regarding a particular Patent, DuPont shall then have the right,
exercisable at its sole discretion, to bring such an action. Any such
infringement action shall be at DuPont's expense, and it shall be solely
entitled to the entire proceeds, if any, of such litigation.

         10.5 Title to Trademarks. The ownership and all goodwill from the use
of any Kos Trademark shall vest in and inure to the benefit of Kos.

         10.6 Trademark License. Kos grants to DuPont a fully paid, exclusive
license to use the Kos Trademark in the Territory for the Term in connection
with the marketing and promotion of the Product as contemplated in this
Agreement, subject to Kos retaining full rights to use the Kos Trademark in the
Territory, and without limiting in any way Kos' rights with respect to the Kos
Trademark outside the Territory.

         10.7 Joint Marks. The Joint Marks shall be jointly filed for and
jointly owned on an equal basis by the Parties, and each Party shall have
co-exclusive rights to use the Joint Marks. During the Term, the Joint Marks
shall be used by the Parties solely in connection with the activities
contemplated by this Agreement as determined by the Marketing Committee. Upon
termination or expiration of this Agreement each Party shall have the right to
continue using the Joint Marks.

         10.8 Maintenance of Trademarks. Kos agrees to search, file, register
and maintain a registration for the Kos Trademark and the Joint Marks in the
Territory for the term of this Agreement for use with the Product. Such expenses
incurred in connection with the Kos Trademarks shall be paid solely by Kos, and
such expenses incurred in connection with the Joint Marks shall be shared
equally by the Parties, and shall be invoiced separate from the calculation of
Net Operating Profit. In the event that the Kos Trademark is not available for
use and registration in connection with the Product in the Territory due to a
rejection of the trademark by a government agency, actual or threatened
opposition, cancellation or litigation as to use and/or registration of the Kos
Trademark by a Third Party, and/or a decision by the Marketing Committee that
use of the Kos Trademark is likely to cause confusion with another's trademark,
Kos shall provide an alternate Kos Trademark and shall develop, search, file,
register and maintain such alternate Kos Trademark at Kos' sole expense,
provided that the selection of such alternate Kos Trademark shall be made by the
Marketing Committee in accordance with Section 6.8(d).

         10.9 Notification of Trademark Litigation. In the event of the
institution of any suit by a Third Party against Kos or DuPont for trademark
infringement involving the marketing, promotion or sale of the Product in
accordance with the annual marketing plan in the Territory, the Party sued shall
promptly notify the other Party in writing.

                                       20
<PAGE>

         10.10 Trademark Infringement. In the event that Kos or DuPont becomes
aware of actual or threatened infringement of a Kos Trademark anywhere in the
Territory, that Party shall promptly notify the other Party in writing. Kos
shall have the sole right, but not the obligation, to investigate and/or bring
an infringement and/or opposition or cancellation action against any Third
Party. Kos shall have full control over the conduct of such investigations and
litigation, including the settlement thereof. The cost of such investigation and
litigation shall be borne entirely by Kos, with Kos being entitled to the entire
proceeds, if any, of such litigation, unless DuPont agrees, at its sole
discretion, within 20 days of such notice, to bear an equal share of such cost,
in which case it shall also be entitled to an equal share of any proceeds of
such litigation. DuPont shall reasonably assist Kos and cooperate in any such
investigation and litigation at Kos' request and at Kos' expense, unless DuPont
has otherwise agreed to participate in the litigation. Should Kos choose not to
bring an infringement action regarding a particular Kos Trademark, DuPont shall
then have the right, exercisable at its sole discretion, to bring such an
action. Any such infringement action shall be at DuPont's expense, and it shall
be solely entitled to the entire proceeds, if any, of such litigation. In the
event that Kos or DuPont becomes aware of actual or threatened infringement of a
Joint Mark anywhere in the Territory, that Party shall promptly notify the other
Party in writing and the Parties shall promptly agree on the most appropriate
course of action with respect to such infringement, including the extent to
which the Parties shall share expenses and recoveries.

         10.11 Information and Settlements. Kos shall keep DuPont informed of
the status of any patent or trademark infringement litigation or settlement
thereof concerning the Product or the Kos Trademark, provided however that no
settlement or consent judgment or other voluntary final disposition of any suit
defended or action brought pursuant to this Article 10 shall be entered into
without the consent of DuPont if such settlement shall require DuPont to be
subject to an injunction or to make a monetary payment or shall otherwise
adversely affect DuPont's rights under this Agreement.

11.      Confidentiality

         11.1 Disclosure of Know-How. To the extent that Kos has disclosed or in
the future discloses to DuPont any Know-How, DuPont shall not acquire any
ownership rights in such Know-How by virtue of this Agreement or otherwise.

         11.2 Confidential Information. Kos and DuPont shall not use or reveal
or disclose to Third Parties any confidential information received from the
other Party or otherwise developed by either Party in the performance of
activities in furtherance of this Agreement without first obtaining the written
consent of the disclosing Party, except as may be otherwise provided in, or
required in order for a Party to fulfill its obligations under, this Agreement.
During and following the Term of this Agreement, this confidentiality obligation
shall not apply to such information that (i) is or becomes a matter of public
knowledge (other than by breach of this Agreement by the receiving Party), or
(ii) is required by law to be disclosed. Following the Term of this Agreement,
this confidentiality obligation shall not apply to such

                                       21
<PAGE>

information that (i) the receiving Party can establish was already known to it
or was in its possession at the time of disclosure, (ii) the receiving Party can
establish was independently developed by persons in its employ who had no
contact with and were not aware of the content of the confidential information,
or (iii) is disclosed to the receiving Party by a Third Party having the right
to do so. The Parties shall take reasonable measures to assure that no
unauthorized use or disclosure is made by others to whom access to such
information is granted.

         Nothing in this Agreement shall be construed as preventing either Party
from disclosing any information received from the other to an Affiliate of the
receiving Party who is necessary for the purposes of enabling the receiving
Party to fulfil its obligations under this Agreement, provided, the receiving
Party shall be responsible for breaches of the confidentiality obligations by
such Affiliate.

         11.3 Public Announcements. No public announcement or other disclosure
to Third Parties concerning the existence of or terms of this Agreement shall be
made, either directly or indirectly, by either Party, except as may be legally
required or as may be required for financial reporting purposes, without first
obtaining the written approval of the other Party and agreement upon the nature
and text of such announcement or disclosure. Each Party agrees that it shall
cooperate fully with the other with respect to all disclosures regarding this
Agreement to the Securities Exchange Commission and any other governmental or
regulatory agencies, including requests for confidential treatment of
proprietary information of either Party included in any such disclosure.

12.      Restrictive Covenants

         12.1 Non-solicitation. Without the prior written consent of the other
Party, each of Kos and DuPont agrees that during the term of this Agreement and
for one year following termination of this Agreement for any reason, it will not
directly or indirectly solicit for purposes of hiring any person employed by the
other Party or who was employed by the other Party within the then prior three
(3) months, or in any manner seek to induce any such person to leave his or her
employment.

         12.2 Non-competition.

              (a) During the Term of this Agreement, neither Party shall
promote, market or sell, or enter into any agreement to promote, market or sell,
in the Territory any oral product for any indication(s) for which the Product
shall have been promoted during the Term of this Agreement ("Other Product"),
other than an

                                       22
<PAGE>

***************************** unless pursuant to a business arrangement with the
other Party or with the other Party's prior written approval.

         (b) For purposes of this Section 12.2, an ****************************
with respect to a Party means (i) any Other Product that is ********************
************* or (ii) any Other Product that is ********************************
********************************************************************************
************************************************.

         (c) Notwithstanding Section 12.2(a) above, if one Party (the "Acquiring
Party") enters into a merger, acquisition or joint venture with a Third Party
who owns, licenses or otherwise controls any Other Product, both Parties shall
engage in good faith negotiations to enter into an arrangement whereby the other
Party (the "Non-Acquiring Party") will co-promote such Other Product. If the
Parties are unable to reach such an agreement within 90 days, then the
Non-Acquiring Party may terminate this Agreement.

13.      Rights And Duties Upon Termination

         13.1 Payment Obligations. In the event that this Agreement is
terminated for any reason prior to the end of the Term, other than termination
by DuPont pursuant to clauses (i), (iii), (iv) or (v) of Section 3.2 or
termination by Kos pursuant to clauses (i) or (iii) of Section 3.2, the
terminating Party shall reimburse the other Party 50% of the non-cancelable
Product Development Costs and Shared Copromotion Expenses incurred or committed
by the other Party as of the date such termination becomes effective, within 10
Business Days following the terminating Party's receipt of invoices from the
other Party.

         13.2 Continuing Obligations. The following provisions shall survive the
termination of this Agreement for any reason: Sections 4.6, 10.1, 10.5, 10.6,
10.7, 14.3, 14.4, 14.5 and 17.4 and Articles 9, 11, 12, 13 and 18. In addition,
any other provision required to interpret and enforce the Parties' rights and
obligations under this Agreement shall also survive, but only to the extent
required for the full observation and performance of this Agreement.

         13.3 Remedies. Termination of this Agreement in accordance with its
provisions shall not limit the remedies that may be otherwise available to
either Party in law or equity. Neither Kos nor DuPont shall be liable under this
Agreement for any indirect, incidental, punitive, exemplary, special or
consequential damages of any kind whatsoever sustained as a result of a breach
of this Agreement.

14.      Representations, Warranties and Indemnification

         14.1 Representations of Kos. Except as disclosed on Schedule 14.1, Kos
represents and warrants that (i) it owns the entire right, title and interest in
the

                                       23
<PAGE>

Patents and Know-How licensed by this Agreement, or otherwise has the right to
grant the license rights under this Agreement, (ii) it has the right to enter
into this Agreement, (iii) that there is nothing in any Third Party agreement
Kos has entered into that in any way will limit Kos' ability to perform all of
the obligations undertaken by Kos under this Agreement, (iv) it will not
encumber, with liens, mortgages, security interests or otherwise, the Patents
and Know-How, (v) it has disclosed to DuPont the complete texts of all Patents
as of the Effective Date as well as all information received by Kos as of the
Effective Date concerning the institution or possible institution of any
interference, opposition, reexamination, reissue, revocation, nullification or
any official proceeding involving a Patent anywhere in the Territory, (vi) it
has received no notice of infringement or misappropriation of any alleged rights
asserted by any Third Party in relation to any technology used in connection
with the manufacture, use or sale of the Product, and it is not aware of any
patent, know-how, trade secret, or other right of any Third Party which could
reasonably be expected to materially adversely affect its ability to carry out
its responsibilities under this Agreement or the manufacture, use or sale of the
Product or the rights granted to DuPont under this Agreement and (vii) it shall
be in compliance with all laws and regulations applicable to the subject matter
of this Agreement, including, without limitation, the Federal Food, Drug, and
Cosmetic Act and the Prescription Drug Marketing Act.

         14.2 Representations of DuPont. DuPont represents and warrants that (i)
it has the right to enter into this Agreement, (ii) there is nothing in any
Third Party agreement DuPont has entered into that in any way will limit
DuPont's ability to perform all of the obligations undertaken by DuPont under
this Agreement, (iii) as of the date hereof, it neither has in development nor
plans to develop any product which will be marketed during the Term which shall
compete with the Product, (iv) DuPont shall be in compliance with all laws and
regulations applicable to the subject matter of this Agreement, including,
without limitation, the Federal Food, Drug, and Cosmetic Act and the
Prescription Drug Marketing Act, (v) the services to be performed by DuPont in
connection with this Agreement will be performed only by individuals who are
employees of DuPont (except as set forth in Section 6.8(e)), and such services
will involve the promotion of the Product in a manner consistent with its
approved labeling and the promotional materials approved by Kos, and (vi) it
shall not represent to any Third Party that it has any proprietary or property
right or interest in the Product, or in any patent relating thereto, or in any
trademark used in connection therewith.

         14.3 Indemnification by Kos. Kos shall defend, indemnify and hold
harmless DuPont and its Affiliates and their officers, directors, shareholders,
employees, agents, representatives, successors and assigns from and against all
claims, complaints, or lawsuits for damages (collectively referred to as
"Claims") arising out of (i) any negligent act or omission, or willful
wrongdoing by Kos in the performance of this Agreement, (ii) the failure by Kos
to comply with any FDA or other governmental requirement, (iii) the infringement
or misappropriation by Kos

                                       24
<PAGE>

of any copyright, trademark, or service mark, as a result of Kos' marketing or
promotion of the Product which is not pursuant to the terms of this Agreement or
the annual marketing plan or in conformity with the direction of the Marketing
Committee, (iv) the infringement or misappropriation of any patent or trade
secret by Kos or DuPont as a result of Kos' or DuPont's marketing or promotion
of the Product under the terms of this Agreement, (v) any breach of any
representation or warranty of Kos, (vi) the manufacturing of the Product by Kos,
and (vii) the labeling or use of the Product. Kos shall not be obligated under
this Section to the extent that the Claim was the result of the non-performance,
negligence or willful misconduct of any employee or agent of DuPont or anyone
acting on behalf of DuPont, including its Affiliates and their officers,
directors, shareholders, employees, agents, representatives, successors and
assigns.

         14.4 Indemnification by DuPont. DuPont shall defend, indemnify and hold
harmless Kos and its Affiliates and their officers, directors, shareholders,
employees, agents, representatives, successors and assigns from and against all
Claims arising out of (i) any negligent act or omission, or willful wrongdoing
by DuPont in the performance of this Agreement, (ii) the failure by DuPont to
comply with any FDA or other governmental requirement, (iii) the infringement or
misappropriation by DuPont of any patent, copyright, trademark, or trade secret,
as a result of DuPont's marketing or promotion of the Product which is not
pursuant to the terms of this Agreement or the annual marketing plan or in
conformity with the direction of the Marketing Committee, and (iv) any breach of
any representation or warranty of DuPont. DuPont shall not be obligated under
this Section to the extent that the Claim was the result of the nonperformance,
negligence or willful misconduct of any employee or agent of Kos or anyone
acting on behalf of Kos, including its Affiliates and their officers, directors,
shareholders, employees, agents, representatives, successors and assigns.

         14.5 Limitations on Indemnification. The obligations to indemnify,
defend, and hold harmless set forth in Sections 14.3 and 14.4 shall be
contingent upon the Party seeking indemnification (the "Indemnitee"): (i)
notifying the indemnifying Party of a claim, demand or suit within five (5)
Business Days of receipt of same; provided, however, that Indemnitee's failure
or delay in providing such notice shall not relieve the indemnifying Party of
its indemnification obligation except to the extent the indemnifying Party is
prejudiced thereby; (ii) allowing the indemnifying Party and/or its insurers the
right to assume direction and control of the defense of any such claim, demand
or suit; (iii) using its best efforts to cooperate with the indemnifying Party
and/or its insurers in the defense of such claim, demand or suit; and (iv)
agreeing not to settle or compromise any claim, demand or suit without prior
written authorization of the indemnifying Party. The Indemnitee shall have the
right to participate in the defense of any such claim, demand or suit referred
to in this Section utilizing attorneys of its choice, at its own expense,
provided, however, that the indemnifying Party shall have full authority and
control to handle any such claim, demand or suit. Kos' indemnification
obligations under

                                       25
<PAGE>

clause (iv) of Section 14.3 shall be limited to the aggregate amount of Net
Operating Profit Kos has received from the sale of the Product under this
Agreement less the amount of such Net Operating Profits paid to DuPont.

         14.6 Insurance. Immediately upon the launch of the Product in the
Territory, and for a period of ************** after the expiration of this
Agreement or the earlier termination thereof, each Party shall obtain and/or
maintain, respectively, at its sole cost and expense, product liability
insurance in amounts, respectively, which are reasonable and customary in the
U.S. pharmaceutical industry for companies of comparable size and activities at
the respective place of business of each Party. Such product liability insurance
shall insure against************************************************************
*************arising out of the manufacture, sale, distribution, or marketing of
the Product in the Territory. Each Party shall provide written proof of the
existence of such insurance to the other Party upon request. Kos acknowledges
that ***********************

15.      Assignment

         Neither Party shall assign or transfer its rights or obligations under
this Agreement without the prior written consent of the other Party, except (i)
to an Affiliate, or (ii) in connection with a merger, or consolidation with, or
the sale to a Third Party of, the entire pharmaceutical business of such Party
or the entire cardiovascular pharmaceutical business of such Party, provided
that in the case of both clauses (i) and (ii) above, the other Party has no
reasonable objection to the Affiliate's or Third Party's ability or willingness
to perform the assigning Party's obligations hereunder or reasonably concludes
that the Affiliate or Third Party places the marketing of the Product at a
competitive disadvantage. Kos acknowledges and agrees that a change in the
structure of DuPont from a general partnership to a corporation shall not
require the prior written consent of Kos.

16.      Notices

         Any notice, request, approval or other document required or permitted
to be given under this Agreement shall be in writing and shall be deemed to have
been given when delivered in person, or sent by overnight courier service,
postage prepaid, or sent by certified or registered mail, return receipt
requested, or by facsimile transmission, to the following addresses of the
Parties and to the attention of the persons identified below (or to such other
address, addresses or persons as may be specified from time to time in a written
notice). Any notices given pursuant to this Agreement shall be deemed to have
been given and delivered upon the earlier of (i) if sent by overnight courier
service, on the date when received at the address set forth below as proven by a
written receipt from the delivery service verifying delivery, or (ii) if sent by
certified or registered mail, three (3) Business Days after mailed by certified
or registered mail postage prepaid and properly addressed, with return receipt
requested, or (iii) if sent by facsimile transmission,

                                       26
<PAGE>

on the day when sent by facsimile as confirmed by automatic transmission report
coupled with certified or registered mail or overnight courier service receipt
proving delivery, or (iv) if delivered in person, on the date of delivery to the
address set forth below as proven by written signature of the recipient.

Kos Pharmaceuticals, Inc:

                          1001 Brickell Bay Drive
                          25th Floor
                          Miami, Florida 33131
                          Facsimile: (305) 577-4596
                          Attention:  Mukesh P. Patel, Vice President, Licensing
                          Attention:  Juan F. Rodriguez, Vice President,
                                      Controller and  Secretary
Copy to:

                          Holland & Knight LLP
                          701 Brickell Avenue
                          Suite 3000
                          Miami, Florida 33131
                          Facsimile: (305) 789-7799
                          Attention: Steven Sonberg, Esq.

DuPont Pharmaceuticals Company:

                          Chestnut Run Plaza
                          974 Centre Road
                          Wilmington, Delaware  19807
                          Facsimile: (302) 992-3109
                          Attention: Executive Vice President,
                                     Cardiovascular/Thrombosis Franchise

Copy to:

                          Chestnut Run Plaza
                          974 Centre Road
                          Wilmington, Delaware  19807
                          Facsimile: (302) 892-8536
                          Attention: Associate General Counsel,
                                     Cardiovascular/Thrombosis Franchise

         Notwithstanding the foregoing, notice of any breach of this Agreement
delivered by a Party under Section 3.2 shall be provided in accordance with the
foregoing provisions to the chief executive officer of the other Party in
addition to the persons identified above.

                                       27
<PAGE>

17.      Miscellaneous

         17.1 Force Majeure. If the performance of any part of this Agreement by
either Party, or of any obligation under this Agreement, is prevented,
restricted, interfered with or delayed by reason of any cause beyond the
reasonable control of the Party liable to perform, unless conclusive evidence to
the contrary is provided, the Party so affected shall, upon giving written
notice to the other Party, be excused from such performance to the extent of
such prevention, restriction, interference or delay, provided that the affected
Party shall use its reasonable best efforts to avoid or remove such causes of
nonperformance and shall continue performance with the utmost dispatch whenever
such causes are removed. When such circumstances arise, the Parties shall
discuss what, if any modification of the terms of this Agreement may be required
in order to arrive at an equitable solution.

         17.2 No Partnership or Joint Venture. It is expressly agreed that Kos
and DuPont shall be independent contractors and that the relationship between
the two Parties shall not constitute a partnership, joint venture or agency.
Neither Kos nor DuPont shall have the authority to make any statements,
representations or commitments of any kind, or to take any action, which shall
be binding on the other, without the prior written consent of the other Party to
do so.

         17.3 Execution In Counterparts. This Agreement may be executed in any
number of counterparts, each of which shall be deemed an original but all of
which together shall constitute one and the same instrument.

         17.4 Governing Law. This Agreement shall be deemed to have been made in
the State of Florida and its form, execution, validity, construction and effect
shall be determined in accordance with the laws of the State of Florida.

         17.5 Waiver Of Breach. The failure of either Party at any time or times
to require performance of any provision hereof shall in no manner affect its
rights at a later time to enforce the same. No waiver by either Party of any
condition or term in any one or more instances shall be construed as a further
or continuing waiver of such condition or term or of another condition or term.

         17.6 Severability. In the event any portion of this Agreement were to
be held illegal, void or ineffective, the remaining portions of this Agreement
shall remain in full force and effect. If any of the terms or provisions of this
Agreement are in conflict with any applicable statute or rule of law, then such
terms or provisions shall be deemed inoperative to the extent that they may
conflict therewith and shall be deemed to be modified to conform with such
statute or rule of law. In the event that the terms and conditions of this
Agreement are materially altered as a result of this Section 17.6, the Parties
shall renegotiate the terms and conditions of this Agreement to resolve any
inequities.

                                       28
<PAGE>

         17.7 Entire Agreement. This Agreement and the Stock Purchase Agreement
shall constitute the entire agreement between the Parties relating to the
subject matter thereof and shall supersede all previous writings and
understandings. No terms or provisions of this Agreement shall be varied or
modified by any prior or subsequent statement, conduct or act of either of the
Parties, except that the Parties may amend this Agreement by written instruments
specifically referring to and executed in the same manner as this Agreement.

18.      Dispute Resolution

         18.1 Internal Resolution. Any dispute, controversy or claim arising out
of or relating to this Agreement, excluding termination, (collectively referred
to as "Dispute") shall be attempted to be settled by the Parties, in good faith,
by submitting each such Dispute to designated senior management representatives
of each Party, who shall meet within seven (7) Business Days as reasonably
requested by either Party to review any Dispute. If the Dispute is not resolved
by the designated representatives by mutual agreement within fourteen (14)
Business Days after a meeting to discuss the Dispute, either Party may at any
time thereafter provide the other written notice specifying the terms of such
Dispute in reasonable detail. Within seven (7) Business Days of receipt of such
notice, the presidents of each Party, or a member of management designated by
them, shall meet at a mutually agreed upon time and location for the purpose of
resolving such Dispute. They will discuss the problems and/or negotiate for a
period of up to twenty (20) Business Days in an effort to resolve the Dispute or
negotiate an acceptable interpretation or revision of the applicable portion of
this Agreement mutually agreeable to both Parties, without the necessity of
formal procedures relating thereto.

         18.2 Arbitration. If the Parties have been unable to resolve a dispute
through the above-described procedures, the Party initiating such procedures
may, in its discretion, within fourteen (14) Business Days after the
above-described procedures have been exhausted, propose non-binding arbitration
in accordance with the CPR Non-Administered Arbitration Rules in effect on the
date of this Agreement. The place of any such arbitration shall be Washington,
DC and it shall be conducted by a sole arbitrator. The Parties may not pursue
any other legal or equitable rights or remedies relating to any dispute until
the conclusion of the arbitration.

         In the event such arbitration is not commenced, the parties may pursue
any available legal or equitable rights or remedies.

                                       29
<PAGE>

         NOW THEREFORE, the Parties, through their authorized officers, have
executed this Agreement as of the date first written above.

                                  KOS PHARMACEUTICALS, INC

                                  By: /S/ DANIEL M. BELL
                                     -------------------------------------------
                                  Name: Daniel M. Bell
                                  Title: President and Chief Executive Officer
                                  Date: May 3, 2000

                                  DUPONT PHARMACEUTICALS COMPANY

                                  By: /S/ NICHOLAS L. TETI
                                     -------------------------------------------
                                  Name: Nicholas L. Teti
                                  Title: President and Chief Executive Officer
                                  Date: May 3, 2000EXHIBIT 10.2

                            STOCK PURCHASE AGREEMENT

         This Stock Purchase Agreement is dated as of May 3, 2000 (this
"Agreement"), between Kos Pharmaceuticals, Inc., a Florida corporation (the
"Company"), and DuPont Pharmaceuticals Company, a Delaware general partnership
("Purchaser").

         A.       The Company and Purchaser have entered into that certain
                  Copromotion and Future Development Agreement dated the date
                  hereof (the "Copromotion Agreement") relating to the
                  copromotion of the Company's Product (as defined in the
                  Copromotion Agreement).

         B.       In connection with, and as a condition of the Company and
                  Purchaser entering into, the Copromotion Agreement, the
                  Company desires to sell to Purchaser, and Purchaser desires to
                  purchase from the Company, shares of the Company's common
                  stock, par value $.01 per share (the "Common Stock"), on the
                  terms and subject to the conditions set forth in this
                  Agreement.

         C.       In connection with, and as a condition of the Company and
                  Purchaser entering into, the Copromotion Agreement, the
                  Company desires to grant Purchaser the option to purchase from
                  the Company certain additional shares of the Company's Common
                  Stock, on the terms and subject to the conditions set forth in
                  this Agreement.

         D.       In connection with, and as a condition of the Company and
                  Purchaser entering into, the Copromotion Agreement and this
                  Agreement, the Company and Purchaser intend to enter into that
                  certain Registration Rights Agreement (the "Registration
                  Rights Agreement").

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained in this Agreement and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, and
intending to be legally bound, the parties agree as follows:

                                   Article 1

                        Purchase and Sale of Common Stock

         1.1 Purchase and Sale of the Shares. Subject to the terms and
conditions hereof, the Company hereby agrees to issue and sell to Purchaser, and
Purchaser hereby agrees to purchase from the Company at the Closing (as
hereinafter defined), 1,250,000 shares of the Company's Common Stock (the

<PAGE>

"Shares") at a purchase price of $16.00 per share, for an aggregate purchase
price for the Shares of $20,000,000 (the "Purchase Price"). The number of Shares
was determined by dividing (i) the Purchase Price by (ii) the average closing
price of a share of Common Stock as quoted on the Nasdaq National Market for the
sixty consecutive trading days immediately preceding the date of this Agreement
(rounded up to the nearest whole dollar).

         1.2 Purchase of Additional Shares.

                  (a) Subject to the terms and conditions hereof, upon the
Company's receipt from the U.S. Food and Drug Administration (the "FDA") of
marketing clearance for the Product (the "Additional Closing Event"), the
Company hereby agrees to issue and sell to Purchaser, and Purchaser hereby
agrees to purchase from the Company at the Additional Closing (as hereinafter
defined), the number of shares of Common Stock (the "Additional Shares")
determined by dividing (i) $5,000,000 by (ii) the average closing price of a
share of Common Stock as quoted on the Nasdaq National Market (or such other
exchange or market on which the Company's Common Stock is then traded) for the
sixty consecutive trading days which immediately precede the date of the
Additional Closing Event, at such price per share, for an aggregate purchase
price for the Additional Shares of $5,000,000 (the "Additional Shares Purchase
Price").

                  (b) The Company shall provide Purchaser with written notice
(the "Additional Closing Event Notice") of the occurrence of the Additional
Closing Event within 3 business days of the occurrence thereof.

                  (c) In the event that, prior to issuance and sale of the
Additional Shares, there shall be an increase or decrease in the number of
issued shares of Common Stock of the Company as a result of a subdivision,
split, reclassification, consolidation of shares or the like, the number of
Additional Shares shall be adjusted so that the adjusted number of such shares
shall be the substantial equivalent of the number of Additional Shares prior to
such change.

         1.3 Option Shares.

                  (a) Subject to the terms and conditions hereof, upon the
occurrence of the Additional Closing Event, the Company hereby grants to
Purchaser the option (the "Option"), exercisable in whole or in part at
Purchaser's sole discretion, to purchase up to a number of shares of the Common
Stock determined by dividing (i) $5,000,000 by (ii) the average of the high and
low trading prices of a share of Common Stock as quoted on the Nasdaq National
Market on the date of the Additional Closing Event (the "Option Shares") at such
price per share, for an aggregate purchase price for the Option Shares of up to
$5,000,000 (the "Option Shares Purchase Price").

                                       2
<PAGE>

                  (b) The Option, or any portion of the Option, shall be
exercised by Purchaser only in accordance with the provisions of this Agreement.
Purchaser shall give to the Company a written notice (the "Exercise Notice") on
or before 5:00 p.m. (Miami time) on the 90th day following the Additional
Closing Event that shall: (i) state the number of Option Shares with respect to
which the Option is being exercised; and (ii) specify a date (other than a
Saturday, Sunday or legal holiday) not less than five nor more than ten days
after the date of such written notice, as the date on which the Option Shares
will be purchased (the "Option Closing Date").

                  (c) In the event that, prior to issuance and sale of the
Option Shares, there shall be an increase or decrease in the number of issued
shares of Common Stock of the Company as a result of a subdivision, split,
reclassification, consolidation of shares or the like, the number of Option
Shares shall be adjusted so that the adjusted number of such shares shall be the
substantial equivalent of the number of Option Shares prior to such change.

         1.4 Closings.

                  (a) The closing of the issuance and sale of the Shares (the
"Closing") shall take place at the offices of Holland & Knight LLP, 701 Brickell
Avenue, Miami, Florida 33131 at 10:00 a.m. (Miami time) on the date three
business days following the satisfaction or waiver of all of the conditions
precedent to the Closing set forth in Section 5.1 (the "Closing Date"), or at
such other place, date and time as may be mutually agreed upon by the Company
and Purchaser. As payment in full for the Shares being purchased by it at the
Closing, Purchaser shall pay to the Company the Purchase Price by wire transfer.
Upon the Purchaser's purchase of the Shares at the Closing, the Company shall
issue and deliver to Purchaser a stock certificate or certificates in definitive
form, registered in the name of Purchaser, representing the number of Shares
purchased at the Closing.

                  (b) Subject to the terms of Section 1.2 and Article 5, the
closing of the sale and purchase of the Additional Shares under this Agreement
(the "Additional Closing") shall be held on the date specified by the Company
and Purchaser within 10 days after the delivery of the Additional Closing Event
Notice (the "Additional Closing Date") at the offices of Holland & Knight LLP,
701 Brickell Avenue, Miami, Florida 33131 at 10:00 a.m. (Miami time), or at such
time and place as the Company and Purchaser may agree. As payment in full for
the Additional Shares being purchased by it at the Additional Closing, Purchaser
shall pay to the Company the Additional Shares Purchase Price by wire transfer.
Upon the Purchaser's purchase of the Additional Shares at the Additional
Closing, the Company shall issue and deliver to Purchaser a stock certificate or
certificates in definitive form, registered in the name of Purchaser,

                                       3
<PAGE>

representing the number of Additional Shares purchased at the Additional
Closing.

                  (c) Subject to the terms of Section 1.3 and Article 5, the
closing of the sale and purchase of the Option Shares under this Agreement (the
"Option Closing") shall be held on the Option Closing Date at the offices of
Holland & Knight LLP, 701 Brickell Avenue, Miami, Florida 33131 at 10:00 a.m.
(Miami time), or at such time and place as the Company and Purchaser may agree.
As payment in full for the Option Shares being purchased by it at the Option
Closing, Purchaser shall pay to the Company the Option Shares Purchase Price by
wire transfer. Upon the Purchaser's purchase of the Option Shares at the Option
Closing, the Company shall issue and deliver to Purchaser a stock certificate or
certificates in definitive form, registered in the name of Purchaser,
representing the number of Option Shares purchased at the Option Closing.

                                   Article 2

                              Additional Agreements

         2.1 Standstill. Notwithstanding any other provision of this Agreement,
without the written consent of the Company, neither Purchaser nor any business
entity that directly, or indirectly through one or more intermediaries, controls
or is controlled by, or is under common control with, Purchaser (its
"Affiliates") will acquire beneficial ownership (which term shall include for
the purposes of this Agreement, without limitation, direct or indirect ownership
or any direct or indirect ability to influence voting in any manner, singly or
as part of a partnership, limited partnership, syndicate or other "Group"
(within the meaning of Section 13(d)(3) of the Securities Exchange Act of 1934,
as amended (the "Exchange Act")) of any securities of the Company entitled to
vote with respect to the election of any directors of the Company ("Voting
Securities"), any security convertible into, exchangeable for or exercisable for
or that may become any Voting Securities or any other right to acquire Voting
Securities, other than the Shares, the Additional Shares, the Option Shares or
shares of the Company's capital stock issuable in respect thereof, including as
a result of a dividend, subdivision, split, reclassification, consolidation of
shares or the like.

         2.2 Acts in Concert with Others; Agreement not to Control. Neither
Purchaser nor its Affiliates shall join a partnership, limited partnership,
syndicate or other group, or otherwise act in concert with any third person, for
the purpose of acquiring, holding, voting or disposing of Voting Securities.

         2.3 Restriction on Transfer of Voting Securities. Notwithstanding any
other provision of this Agreement (including, without limitation, the provisions
of Section 2.4), neither Purchaser nor its Affiliates shall dispose of
beneficial

                                       4
<PAGE>

ownership or voting control of any of the Shares or any right thereto (or any
securities issuable in respect thereof) ("Transfer"), except as follows: (i)
375,000 Shares may be Transferred commencing on the date the Company receives
from the FDA marketing clearance for the Product; (ii) 375,000 Shares may be
Transferred commencing on the one year anniversary of the date the Company
receives from the FDA marketing clearance for the Product; (iii) 500,000 Shares
may be Transferred commencing on the date five years from the date hereof; (iv)
the Additional Shares may be Transferred commencing on the date five years from
the date hereof; (v) one-half of the Option Shares actually purchased by
Purchaser under this Agreement may be Transferred commencing on the one year
anniversary of the Option Closing Date; and (vi) one-half of the Option Shares
actually purchased by Purchaser under this Agreement may be Transferred
commencing on the date five years from the date hereof. In the event that there
shall be an increase or decrease in the number of issued shares of Common Stock
of the Company as a result of a subdivision, split, reclassification,
consolidation of shares or the like, the number of Shares, Additional Shares and
Option Shares in the preceding sentence shall be adjusted, as appropriate, so
that the adjusted number of such shares shall be the substantial equivalent of
the number of such Shares, Additional Shares or Option Shares prior to such
change.

         2.4 Right of First Refusal. If Purchaser or any of its Affiliates
desires to dispose of beneficial ownership of any or all of the Voting
Securities beneficially owned by Purchaser or such Affiliate (the "Offered
Stock"), Purchaser or such Affiliate shall first give written notice (a
"Transfer Notice") thereof to the Company, identifying whether the transaction
will occur on the open market or as a private transaction and the number of
Voting Securities sought to be transferred. If the transaction is to be a
private transaction, the Transfer Notice shall also identify the proposed
transferee, the proposed purchase price (the "Offered Price"), if applicable,
the terms of the proposed transaction including the proposed transaction date
and a copy of any written offer or other writing setting forth the terms and
conditions of the proposed transaction. Such Transfer Notice shall constitute an
irrevocable offer by Purchaser or such Affiliate to sell all of the Offered
Stock to the Company at the market price at the close of trading on the day the
offer is accepted in writing by the Company or, if a private transaction is
proposed, at the Offered Price and upon the same terms and conditions as
Purchaser or such Affiliate is willing to dispose the Offered Stock to the
proposed transferee. If a private transaction is proposed, to the extent the
consideration proposed to be paid by the proposed transferee consists of
property other than cash, the reasonable cash equivalent of such property, and
the manner of determining the same, shall be stated in such Transfer Notice.
Once given, a Transfer Notice may not be modified or amended except with the
written consent of the Company. Within the five (5) business day period, or if a
private transaction is proposed within the twenty-one (21) day period, following
the giving of the Transfer Notice (the "Offer Period"), the Company may elect,
by giving written notice of such election to

                                       5
<PAGE>

Purchaser or such Affiliate, to purchase all but not less than all of the
Offered Stock. If the Company does not elect, by notice in writing given to
Purchaser or such Affiliate within the Offer Period, to purchase all (but not
less than all) of the Offered Stock, then Purchaser or such Affiliate shall be
free to dispose of all of the Offered Stock, if on the open market, within 180
days of the end of the Offer Period, or, if a private transaction is proposed,
within 90 days of the end of the Offer Period to the original proposed
transferee at a price not lower than the Offered Price and upon the terms
stipulated in the Transfer Notice in all material respects. If such Offered
Stock is not so disposed of by Purchaser or such Affiliate within such 180 or 90
day period, Purchaser or such Affiliate shall continue to hold the Voting
Securities subject to all of the terms and conditions of this Agreement and may
not sell any Voting Securities without again complying with all of the
provisions hereof.

         2.5 Approvals and Consents; Cooperation.

                  (a) The Company and Purchaser shall cooperate with each other
and use (and shall cause their respective Subsidiaries to use) their respective
commercially reasonable best efforts to take or cause to be taken all actions,
and do or cause to be done all things, necessary, proper or advisable under this
Agreement and applicable Laws to consummate and make effective the sale of the
Shares, the Additional Shares and the Option Shares (the "Sale") and the other
transactions contemplated by this Agreement as soon as practicable, including
preparing and filing as promptly as practicable all documentation to effect all
necessary applications, notices, petitions, filings and other documents and to
obtain as promptly as practicable all permits, consents, approvals and
authorizations necessary or advisable to be obtained from any third party and/or
any Governmental Entity (as defined in Section 3.6) in order to consummate the
Sale or any of the other transactions contemplated by this Agreement.

                  (b) In particular, the Company and Purchaser each agree to use
commercially reasonable efforts to take, or cause to be taken, all appropriate
action, and do, or cause to be done, such things as may be necessary under
federal or state securities laws or the Hart-Scott-Rodino Antitrust Improvements
Act of 1976, as amended (the "HSR Act") applicable to or necessary for, and will
file as soon as reasonably practicable and, if appropriate, use commercially
reasonable efforts to have declared effective or approved, all documents and
notifications with the Securities and Exchange Commission (the "SEC") and other
governmental or regulatory bodies that they deem necessary or appropriate for,
the consummation of the Sale or any of the other transactions contemplated
hereby and each party shall give the other information reasonably requested by
such other party pertaining to it and its Subsidiaries to enable such other
party to take such actions.

                                       6
<PAGE>

         2.6 SEC Filings; De-registration. The Company shall use its best
efforts to make all required filings under the Exchange Act in a timely manner.
The Company shall use its best efforts to prevent its Common Stock from being
de-registered from the Nasdaq National Market or de-registered under the
Exchange Act.

         2.7 Publicity. Any press release relating to the Sale and this
Agreement shall be made in accordance with Section 11.3 of the Copromotion
Agreement.

         2.8 Expenses. Whether or not the Sale is consummated, all costs and
expenses incurred in connection with this Agreement, the Sale and the other
transactions contemplated by this Agreement shall be paid by the party incurring
such expense.

         2.9 Antitakeover Statutes. If any Antitakeover Statute (as defined in
Section 3.10) is or may become applicable to the Sale or the other transactions
contemplated by this Agreement, each of Purchaser and the Company and their
board of directors shall grant such approvals and take such lawful actions as
are necessary so that such transactions may be consummated as promptly as
practicable on the terms contemplated by this Agreement and otherwise act to
eliminate or minimize the effects of such statute or regulation on such
transactions.

                                   Article 3

                  Representations and Warranties of the Company

         The Company represents and warrants to Purchaser as of the date hereof
as follows:

         3.1 Authorization of Agreements, etc. The execution and delivery by the
Company of this Agreement, the performance by the Company of its obligations
hereunder, the issuance, sale and delivery of the Shares and the issuance and
delivery of the Additional Shares and the Option Shares have been duly
authorized by all requisite corporate action and will not result in any
violation of, be in conflict with, or constitute a default under, with or
without the passage of time or the giving of notice: (a) any provision of the
Company's Articles of Incorporation, as amended, or Bylaws; (b) any provision of
any judgment, decree or order to which the Company is a party or by which it is
bound; (c) any material contract or agreement to which the Company is a party or
by which it is bound; or (d) any statute, rule or governmental regulation
applicable to the Company, except where such violation, conflict, or default
would not have a Company Material Adverse Effect (as defined in Section 3.5).

         3.2 Valid Issuance of Common Stock. The Shares, the Additional Shares
and the Option Shares have been duly authorized and, when issued,

                                       7
<PAGE>

sold and delivered in accordance with this Agreement for the consideration
expressed herein will be validly issued, fully paid and nonassessable with no
personal liability attaching to the ownership thereof and will be free and clear
of all liens, charges and encumbrances of any nature whatsoever except for
restrictions on transfer under this Agreement and under applicable Federal and
state securities laws.

         3.3 Validity. This Agreement has been duly executed and delivered by
the Company and constitutes the legal, valid and binding obligation of the
Company, enforceable in accordance with its terms except (i) as limited by
applicable bankruptcy, insolvency, reorganization, moratorium, and other laws of
general application affecting enforcement of creditors' rights generally, (ii)
as limited by laws relating to the availability of specific performance,
injunctive relief, or other equitable remedies, and (iii) to the extent the
indemnification provisions contained in this Agreement may be limited by
applicable Federal or state securities laws.

         3.4 Capitalization. As of May 1, 2000, the authorized capital stock of
the Company consists of 50,000,000 shares of Common Stock, and 10,000,000 shares
of preferred stock, par value $.01 per share, of which 18,401,814 shares of
Common Stock are outstanding, no shares of preferred stock are outstanding, and
warrants, options or convertible securities relating to the issuance by the
Company of up to 16,183,300 shares of its Company's Common Stock are
outstanding, not including up to an aggregate of 8,000,000 options or shares of
common stock issuable under either the 1996 Kos Pharmaceuticals, Inc. Stock
Option Plan and the 1999 Kos Pharmaceuticals, Inc. Employee Stock Purchase Plan.
All of the issued and outstanding shares of the Company's Common Stock are duly
and validly issued and outstanding and are fully paid and nonassessable.

         3.5 Organization, Good Standing and Qualification. Each of the Company
and each of its Subsidiaries is a corporation or limited liability company duly
organized, validly existing and in good standing (where such concept is
recognized) under the laws of its respective jurisdiction of organization. Each
of the Company and each of its Subsidiaries has all requisite corporate or
limited liability company power and authority to own and operate its respective
properties and assets and to carry on its business as presently conducted. Each
of the Company and each of its Subsidiaries is qualified to do business and is
in good standing as a foreign corporation or limited liability company in each
jurisdiction (where such concept is recognized) where the ownership or operation
of its properties or conduct of its business requires such qualification, except
where the failure to be so qualified or in such good standing, when taken
together with all other such failures, is not reasonably likely to have a
Company Material Adverse Effect (as defined below) or impair the ability of the
Company, Purchaser or any of their respective Subsidiaries, following
consummation of the Sale, to conduct any

                                       8
<PAGE>

material business or operations in any jurisdiction where they are now being
conducted. All of the outstanding equity interests in each such Subsidiary have
been validly issued and are fully paid and non-assessable and owned by the
Company free and clear of all pledges, claims, liens, charges, encumbrances and
security interests of any kind or nature whatsoever. The Company has made
available to Purchaser a complete and correct copy of the Company's Articles of
Incorporation and Bylaws (or similar documents), each as amended to date. The
Company's Articles of Incorporation and Bylaws so made available are in full
force and effect.

         As used in this Agreement, (a) "Subsidiary" means, with respect to the
Company or Purchaser, as the case may be, any entity, whether incorporated or
unincorporated, of which at least fifty percent (50%) of the securities or
ownership interests having by their terms ordinary voting power to elect fifty
percent (50%) of the board of directors or other persons performing similar
functions is directly or indirectly owned or controlled by such party or by one
or more of its respective Subsidiaries or by such party and any one or more of
its respective Subsidiaries, and (b) "Company Material Adverse Effect" means any
change in or effect on the business of the Company and its Subsidiaries that is,
or is reasonably likely to be, materially adverse to the business, operations or
assets (including intangible assets), liabilities (contingent or otherwise),
prospects, condition (financial or otherwise) of the Company and its
Subsidiaries, taken as a whole.

         3.6 Governmental Filings. Other than any filings and/or notices
required pursuant to the HSR Act, federal securities laws and state securities
or "blue sky" laws, no notices or other filings are required to be made by the
Company with, nor are any consents, registrations, approvals, permits or
authorizations required to be obtained by the Company from, any governmental or
regulatory authority, agency, commission, body or other governmental entity
("Governmental Entity"), in connection with the execution and delivery of this
Agreement by the Company and the consummation by the Company of the Sale and the
other transactions contemplated hereby, except those that the failure to make or
obtain are not, individually or in the aggregate, reasonably likely to have a
Company Material Adverse Effect or prevent, materially delay or materially
impair the ability of the Company to consummate the transactions contemplated by
this Agreement.

         3.7 Company Reports; Financial Statements. The Company and, to the
extent applicable, each of its then or current Subsidiaries has made all filings
required to be made by it with the SEC since December 16, 1996 (collectively,
the "Company Reports"). As of their respective dates, the Company Reports
complied in all material respects with the requirements of applicable statutes
and regulations and did not, and any Company Reports filed with the SEC prior to
the Sale will not, contain any untrue statement of a material fact or omit to
state a material fact required to be stated therein or

                                       9
<PAGE>

necessary to make the statements made therein, in light of the circumstances in
which they were made, not misleading. Each of the balance sheets included in or
incorporated by reference into the Company Reports (including the related notes
and schedules) presents fairly, or will present fairly, the financial position
of the Company and its Subsidiaries as of its date and each of the statements of
income and of changes in financial position included in or incorporated by
reference into the Company Reports (including any related notes and schedules)
presents fairly, or will present fairly, the results of operations, retained
earnings and changes in financial position, as the case may be, of the Company
and its Subsidiaries for the periods set forth therein (except as otherwise
noted therein and subject, in the case of unaudited statements, to notes and
normal year-end audit adjustments that will not be material in amount or
effect), in each case in accordance with generally accepted accounting
principles ("GAAP") consistently applied during the periods involved, except, in
the case of unaudited financial statements, as permitted by SEC Form 10-Q, and
except as may be noted therein. The Company has not, on or prior to the date
hereof, filed any other definitive reports or statements with the SEC since
March 23, 2000.

         3.8 Litigation and Liabilities. Except for matters which are disclosed
in the Company Reports or those matters which are not, individually or in the
aggregate, reasonably likely to have a Company Material Adverse Effect or
prevent or materially delay or materially impair the ability of the Company to
consummate the transactions contemplated by this Agreement, there are no (i)
civil, criminal, administrative or regulatory actions, suits, claims, hearings,
investigations or proceedings pending or, to the actual knowledge of the
Company's officers and directors, threatened against the Company or any of its
Subsidiaries or (ii) material obligations or liabilities of the Company, whether
or not accrued, contingent or otherwise and whether or not required to be
disclosed in the Company Reports.

         3.9 Compliance. Other than those matters which are disclosed in the
Company Reports, the Company is not in material default or violation of, (a) its
Articles of Incorporation or Bylaws, (b) any law, ordinance, rule, regulation,
order, judgment, decree, arbitration award, license or permit of any
Governmental Entity (collectively, "Laws") applicable to the Company or by which
its properties are bound, or (c) any material contract to which the Company or
any of its Subsidiaries is a party or by which the Company or any of its
Subsidiaries or its or any of their respective properties are bound or affected,
except for any such material defaults or violations that, individually or in the
aggregate, will not have a Company Material Adverse Effect, or prevent or
materially delay the transactions contemplated by this Agreement. No material
change is required in the Company's processes, properties or procedures in order
to comply in all material respects with any Laws, and the Company has not
received any notice of any material noncompliance with any such Laws that has
not been cured.

                                       10
<PAGE>

         3.10 Antitakeover Statutes. The board of directors of the Company has
taken all necessary action to approve the transactions contemplated by this
Agreement such that the restrictions under Section 607.0901 of the Florida
Business Corporation Act shall not apply to such transactions. No "fair price,"
"moratorium," "control share acquisition" or other antitakeover statute or
regulation (each, an "Antitakeover Statute") is applicable to the Sale, this
Agreement or the other transactions contemplated hereby.

         3.11 Intellectual Property. The representations and warranties as set
forth in Section 14.1 of the Copromotion Agreement are correct and true as of
the Closing Date and will be correct and true as of the Additional Closing Date
and the Option Closing Date.

         3.12 Brokers and Finders. Neither the Company nor any of its
Subsidiaries, officers, directors or employees has employed any broker or finder
or incurred any liability for any brokerage fees, commissions or finders' fees
in connection with the Sale or the other transactions contemplated by this
Agreement.

         3.13 Certain Agreements. Neither the Company nor its Subsidiaries has
violated any provision of, or committed or failed to perform any act which, with
or without notice, lapse of time, or both, is reasonably likely to constitute a
default under the provisions of, any material contract of the Company or such
Subsidiary, and neither the Company nor any of its Subsidiaries has received
notice that any party to any such contract intends to cancel, terminate or
otherwise modify the terms of such contract, except in each case, as is not
reasonably likely to have, individually or in the aggregate, a Company Material
Adverse Effect.

         3.14 No Required Vote of Company Stockholders. There is no vote of the
shareholders of the Company required to adopt this Agreement or to approve the
Sale or the transactions contemplated hereby.

         3.15 Licenses and Permits. The Company and each Subsidiary has obtained
all material licenses, registrations, permits, approvals and other governmental
authorizations required to conduct its business as described in the Company
Reports. Such licenses are in full force and effect and neither the Company nor
any Subsidiary has received notice of proceedings relating to the revocation or
modification of any such license, permit, approval and other governmental
authorization.

                                   Article 4

                   Representations and Warranties of Purchaser

         Purchaser represents and warrants to the Company as of the date hereof
as follows:

                                       11
<PAGE>

         4.1 Authorization. The execution and delivery by Purchaser of this
Agreement and the performance by Purchaser of its obligations hereunder have
been duly authorized by all requisite partnership action.

         4.2 Validity. This Agreement has been duly executed and delivered by
Purchaser and constitutes the legal, valid and binding obligation of Purchaser,
enforceable in accordance with its terms except:

                  (a) as limited by applicable bankruptcy, insolvency,
reorganization, moratorium, and other laws of general application affecting
enforcement of creditors' rights generally;

                  (b) as limited by laws relating to the availability of
specific performance, injunctive relief, or other equitable remedies; and

                  (c) to the extent the indemnification provisions contained in
this Agreement may be limited by applicable Federal or state securities laws.

         4.3 Investment Representations.

                  (a) Purchaser is an "accredited investor" within the meaning
of Rule 501 of Regulation D under the Securities Act of 1933, as amended (the
"Securities Act") and was not organized for the specific purpose of acquiring
the Shares, the Additional Shares or the Option Shares;

                  (b) Purchaser has sufficient knowledge and experience in
investing in companies similar to the Company in terms of the Company's stage of
development so as to be able to evaluate the risks and merits of its investment
in the Company and it is able financially to bear the risks thereof;

                  (c) it is the present intention that the Shares, the
Additional Shares and the Option Shares being purchased by Purchaser are being
acquired for Purchaser's own account for the purpose of investment and not with
a present view to or for sale in connection with any distribution thereof;

                  (d) Purchaser understands that:

                           (i) the Shares, the Additional Shares and the Option
Shares have not been registered under the Securities Act by reason of their
issuance in a transaction exempt from the registration requirements of the
Securities Act pursuant to Section 4(2) thereof or Rule 505 or 506 promulgated
under the Securities Act;

                           (ii) the Shares, the Additional Shares and the Option
Shares must be held indefinitely unless a subsequent disposition thereof is
registered under the Securities Act or is exempt from such registration;

                                       12
<PAGE>

                           (iii) the Shares, the Additional Shares and the
Option Shares will bear a legend to such effect; and

                           (iv) the Company will make a notation on its transfer
books to such effect; and

                  (e) the Company has made available to Purchaser all documents
and information that the undersigned has requested relating to an investment in
the Company.

         4.4 Intellectual Property. The representations and warranties as set
forth in Section 14.2 of the Copromotion Agreement are correct and true as of
the Closing Date and will be correct and true as of the Additional Closing Date
and the Option Closing Date.

         4.5 Brokers and Finders. Neither the Purchaser nor any of its
Subsidiaries, officers, directors or employees has employed any broker or finder
or incurred any liability for any brokerage fees, commissions or finders' fees
in connection with the Sale or the other transactions contemplated by this
Agreement.

                                   Article 5

                                   Conditions

         5.1 Conditions to Each Party's Obligations for the Sale. The respective
obligations of each party to effect the Sale as it pertains to both the Shares,
the Additional Shares and the Option Shares are subject to the satisfaction or
waiver at or prior to each of the Closing, the Additional Closing and the Option
Closing of each of the following conditions:

                  (a) No Injunctions or Restraints. (i) No court or Governmental
Entity of competent jurisdiction shall have enacted, issued, enforced or entered
any statute, rule, regulation, judgment, decree, injunction or other order
(whether temporary, preliminary or permanent) that is in effect and restrains,
enjoins or otherwise prohibits consummation of the Sale (collectively, an
"Order"); provided however, that prior to invoking this provision, each party
shall use its commercially reasonable best efforts to have any such Order lifted
or withdrawn, and (ii) no Governmental Entity shall have instituted any
proceeding seeking any such Order;

                  (b) Opinion of Counsel. Purchaser shall have received the
opinion of Holland & Knight LLP in substantially the form attached hereto as
Exhibit 5.1(b) at or prior to the Closing and another opinion in substantially
the same form at or prior to each of the Additional Closing and the Option
Closing;

                                       13
<PAGE>

                  (c) Officer's Certificates. The representations and warranties
of the Company contained in Article 3 shall be true and correct in all material
respects on and with the same force and effect as though such representations
and warranties had been made on and as of the Closing Date, the Additional
Closing Date and the Option Closing Date. The representations and warranties of
the Purchaser contained in Article 4 shall be true and correct in all material
respects on and with the same force and effect as though such representations
and warranties had been made on and as of the Closing Date, the Additional
Closing Date and the Option Closing Date. All the terms, covenants and
conditions of this Agreement and the other agreements contemplated herein to be
complied with and performed by the Company and the Purchaser prior to the
Closing, the Additional Closing or the Option Closing shall have been duly
complied with and performed in all material respects. The Company shall have
delivered to Purchaser a certificate to such effect at or prior to the Closing,
dated the Closing Date, the Additional Closing, dated the Additional Closing
Date, and the Option Closing, dated the Option Closing Date, signed by its
President;

                  (d) Copromotion Agreement. The Copromotion Agreement shall not
have expired or been terminated and neither party shall be in default
thereunder;

                  (e) Registration Rights Agreement. The Company and Purchaser
shall have entered into the Registration Rights Agreement and such agreement
shall not have expired or been terminated prior to the Additional Closing or the
Option Closing and neither party shall be in default thereunder; and

                  (f) Regulatory Consents. Any waiting period under the HSR Act
shall have expired or terminated.

         5.2 Conditions to Each Party's Obligations for the Sale of the
Additional Shares and the Option Shares. In addition to those conditions set
forth in Section 5.1, the respective obligations of each party to effect the
Sale as it pertains to the Additional Shares and the Option Shares is subject to
the satisfaction or waiver at or prior to the Additional Closing or the Option
Closing of each of the following conditions:

                  (a) Additional Closing Event. The Additional Closing Event, as
set forth in Section 1.2(a), shall have occurred.

                                   Article 6

                                 Miscellaneous

         6.1 Termination. This Agreement shall terminate upon the expiration or
earlier termination of the Copromotion Agreement; provided however, that

                                       14
<PAGE>

Section 2.1 shall survive for one year following the termination of the
Copromotion Agreement for any reason other than the expiration of the Term, and
provided further that Section 2.4 shall survive for one year following the
termination of the Copromotion Agreement for any reason.

         6.2 Brokerage. Each party hereto will indemnify and hold harmless the
other against and in respect of any claim for brokerage or other commissions
relative to this Agreement or to the transactions contemplated hereby, based in
any way on agreements, arrangements or understandings made or claimed to have
been made by such party with any third party.

         6.3 Parties in Interest. All representations, covenants and agreements
contained in this Agreement by or on behalf of any of the parties hereto shall
bind and inure to the benefit of the respective successors and assigns of the
parties hereto whether so expressed or not.

         6.4 Notices. All notices, requests, consents, demands, and other
communications under this Agreement shall be in writing and shall be deemed to
have been duly given on the date of service if served personally on the party to
whom notice is to be given, on the date of transmittal of services via telecopy
to the party to whom notice is to be given (with a confirming copy delivered
within 24 hours thereafter), or on the third day after mailing if mailed to the
party to whom notice is to be given, by first class mail, registered or
certified, postage prepaid, or overnight mail via a nationally recognized
courier providing a receipt for delivery and properly addressed as follows:

If to the Company:                  Kos Pharmaceuticals, Inc.
                                    1001 Brickell Bay Drive
                                    25th Floor
                                    Miami, FL  33131
                                    Fax (305) 577-4596
                                    Attention: President

with a copy to:                     Holland & Knight LLP
                                    701 Brickell Avenue
                                    Suite 3000
                                    Miami, FL 33131
                                    Fax (305) 789-7799
                                    Attention: Steven Sonberg, Esq.

                                       15
<PAGE>

If to Purchaser:                    DuPont Pharmaceuticals Company
                                    Chestnut Run Plaza
                                    974 Centre Road
                                    Wilmington, DE  19807
                                    Fax (302) 992-2402
                                    Attention: Stephen Potter, Senior Vice
                                               President of Portfolio and
                                               Business Development

with a copy to:                     DuPont Pharmaceuticals Company
                                    Chestnut Run Plaza
                                    974 Centre Road
                                    Wilmington, DE  19807
                                    Fax (302) 892-8899
                                    Attention: Robert E. Pelzer, Esq.,
                                               General Counsel

with a copy to:                     Ballard Spahr Andrews & Ingersoll, LLP
                                    1735 Market Street, 51st Floor
                                    Philadelphia, PA 19103-7599
                                    Fax (215) 864-8999
                                    Attention:  Justin P. Klein, Esq.

Any party may change its address for purposes of this paragraph by giving notice
of the new address to each of the other parties in the manner set forth above.

         6.5 Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Florida for all purposes and in all
respects, without regard to the conflict of law provisions of such state.

         6.6 Dispute Resolution. Disputes arising under this Agreement shall be
resolved in accordance with Article 18 of the Copromotion Agreement.

         6.7 Entire Agreement. This Agreement, the Registration Rights Agreement
and the Copromotion Agreement, including the attachments thereto, constitute the
sole and entire agreement of the parties with respect to the subject matter
hereof.

         6.8 Counterparts. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         6.9 Amendments and Waivers. This Agreement may be amended or modified,
and provisions hereof may be waived, only with the written consent of the
Company and Purchaser.

                                       16
<PAGE>

         6.10 Severability. If any provision of this Agreement shall be declared
void or unenforceable by any judicial or administrative authority, the validity
of any other provision and of the entire Agreement shall not be affected
thereby.

         6.11 Titles and Subtitles. The titles and subtitles used in this
Agreement are for convenience only and are not to be considered in construing or
interpreting any term or provision of this Agreement.

                                       17
<PAGE>

         NOW THEREFORE, the Company and Purchaser have executed this Stock
Purchase Agreement as of the date first above written.

KOS PHARMACEUTICALS, INC.

By:_________________________________
Name:
Title:

DUPONT PHARMACEUTICALS COMPANY

By:_________________________________
Name:
Title:

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