<PAGE>

                                                                    EXHIBIT 4.19

                                     AMGEN

                     FREESTANDING DIALYSIS CENTER AGREEMENT

     This Agreement ("Agreement"), between Amgen USA Inc. ("Amgen"), a
wholly-owned subsidiary of Amgen Inc., and National Medical Care, Inc.,
including all subsidiaries and affiliates that are at least fifty and one-tenth
percent (50.10%) owned by National Medical Care, Inc. and listed on Appendix B,
(collectively, "NMC"), sets forth the terms and conditions for the purchase of
EPOGEN(R) (Epoetin alfa) and Aranesp(R) (darbepoetin alfa) (collectively,
"Products") by NMC, exclusively for the treatment of dialysis patients.

1.   TERM OF AGREEMENT.  The "Term" of this Agreement shall be defined as
     January 1, 2004 ("Commencement Date") through January 31, 2006
     ("Termination Date").

2.   QUALIFIED PURCHASES.  All terms contained herein apply only to purchases
     made hereunder, as confirmed by Amgen ("Qualified Purchases"), by NMC and,
     subject to the terms of Section 11, all Affiliates (as such term is defined
     in Section 11 below) opened, acquired, or managed by NMC during the Term,
     for so long as such Affiliates remain at least fifty and one-tenth percent
     (50.10%) owned or managed by National Medical Care, Inc., through
     wholesalers chosen by NMC and authorized by Amgen to participate in the
     program ("Authorized Wholesalers") or directly from Amgen. In addition, and
     also subject to the terms of Section 11, Renaissance Health Care, Inc.,
     Optimal Renal Care, L.L.C., Integrated Renal Care of the Pacific, LLC
     and/or any joint venture of NMC in which NMC holds at least a fifty and
     one-tenth percent (50.10%) ownership interest, will also be eligible to
     participate, although not required to purchase under this Agreement. Amgen
     agrees to reasonably approve Authorized Wholesalers requested by NMC. The
     option to purchase on a direct basis from Amgen is subject to receipt and
     approval, not to be unreasonably withheld, of an "Application for Direct
     Ship Account".

3.   PRICING.  See Appendix A.

4.   PAYMENT TERMS.  The terms and conditions of this Agreement shall apply
     whether NMC and/or Affiliates purchase Products through an Authorized
     Wholesaler or from Amgen directly.

5.   DISCOUNT.  NMC shall qualify for discounts and incentives subject to
     material compliance with the terms and conditions of this Agreement as well
     as the schedules and terms set forth in Appendix A. Discounts in arrears
     will be paid by Amgen in the form of a [*] to NMC's corporate headquarters,
     and Amgen Inc. hereby guarantees Amgen's obligation to pay all discounts
     earned by NMC hereunder. Discounts in arrears will be calculated in
     accordance with the terms set forth in Appendix A. For purposes of all of
     the discounts paid in arrears contained herein, including, without
     limitation, those discounts and incentives provided in Appendix A, if any
     Affiliates are added to or deleted from this Agreement during any quarter,
     Amgen shall appropriately adjust NMC's purchases for the relevant periods
     (i) for deleted Affiliates, by excluding purchases by such Affiliates
     effective from the effective date of their deletion and during the relevant
     quarter used for comparison, or (ii) for added Affiliates, by including any
     purchases made by acquired Affiliates effective from the date they are
     added to the list of Affiliates on Appendix B and during the relevant
     quarter used for comparison, and by including any purchases made by any de
     novo Affiliates commencing in the quarter in which they commence
     operations. Amgen and NMC agree that, for purposes of determining
     eligibility for and calculation of all discounts and all incentives
     provided in this Agreement (including, without limitation, all discounts
     and incentives as are set forth in Appendix A), a Qualified Purchase of
     EPOGEN(R) or Aranesp(R) shall be deemed made on the date of invoice to NMC
     from an Authorized Wholesaler. Upon any termination of this Agreement,
     Amgen shall pay to NMC all discounts and incentives earned by NMC through
     the date of termination. Failure of NMC to qualify for or receive any
     particular discount or incentive hereunder shall not automatically affect
     its qualification for or receipt of any other discount or incentive
     provided under this Agreement.

6.   PAYMENT OF DISCOUNTS.  Any discount (hereinafter defined as including a
     discount at time of purchase, rebate, incentive or other concession
     impacting the total pricing of a Product) earned hereunder which is
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<PAGE>

     applicable to purchases of EPOGEN(R) shall be calculated in accordance with
     this Agreement, based on Qualified Purchases, using the [*] as the basis
     for the calculation price, and shall be paid in the form of a [*] to NMC's
     corporate headquarters, except as otherwise provided hereunder. Any
     discount earned hereunder which is applicable to purchases of Aranesp(R)
     used to treat dialysis patients shall be calculated in accordance with this
     Agreement, based on Qualified Purchases, using [*] as the basis for the
     calculation price. NMC and Affiliates shall make available to Amgen any
     records concerning NMC's and Affiliates' purchase amounts that Amgen or its
     auditors may reasonably request for purposes of verifying discounts. [*] In
     the event of a discrepancy between data provided by NMC and that provided
     by an Authorized Wholesaler, verifiable data submitted by NMC shall be
     used. Amgen will use its best efforts to make any discount (excluding
     discounts at time of purchase) pursuant to this Agreement available in
     accordance with the terms referenced in Appendix A. Availability of
     discounts is contingent upon Amgen receiving all relevant purchase data
     from all Authorized Wholesalers designated by NMC, in a form reasonably
     acceptable to Amgen, detailing NMC's and Affiliates' Qualified Purchases of
     Products for the relevant period, along with any other data required by the
     terms of Appendix A. In the event of any purchases directly from Amgen, all
     such purchase data shall be included in the calculation of all discounts.
     In no event shall Amgen pay any discount on Products distributed by NMC or
     Affiliates to non-Affiliates of NMC. In the event that Amgen is notified in
     writing that National Medical Care, Inc. and/or any of its subsidiaries or
     Affiliates (the "Acquiree") is acquired by another entity or a change of
     control otherwise occurs with respect to the Acquiree, any discount or
     rebate which may have been earned and vested hereunder prior to the
     effective date of the acquisition shall be paid in the form of a [*] to
     Fresenius Medical Care North America's corporate headquarters subject to
     the conditions described herein.

7.   TREATMENT OF DISCOUNTS.  (a) The parties agree that they will account for
     any discount or rebate earned hereunder in a way that complies with all
     applicable federal, state, and local laws and regulations, including
     without limitation, Section 1128B(b) of the Social Security Act and its
     implementing regulations, and if required by such statutes or regulations
     (1) claim the benefit of such discount received, in whatever form, in the
     fiscal year in which such discount was earned or the year after, (2) fully
     and accurately report the value of such discount in any cost reports filed
     under Title XVIII or Title XIX of the Social Security Act, or a state
     health care program, and (3) provide, upon request by the U.S. Department
     of Health and Human Services or a state agency or any other federally
     funded state health care program, the information furnished by Amgen
     concerning the amount or value of such discount. NMC agrees that it will
     advise all Affiliates, in writing, of any discount received by NMC's
     corporate headquarters hereunder with respect to purchases made by such
     Affiliates and that NMC will advise said Affiliates as to their requirement
     under the Agreement to account for any such discount in accordance with the
     above stated requirements.

     (b) In order to assist NMC in its compliance with its obligations as set
     forth in Section 7(a) immediately above, Amgen agrees that, along with the
     quarterly delivery of its payment of the discounts earned hereunder, it
     will provide to NMC on a quarterly basis a statement stating the incentives
     and discounts earned by NMC for such quarter.

8.   [*]

9.   OWN USE.  NMC hereby certifies that Products purchased hereunder will be
     for the "own use" by NMC and the Affiliates of NMC. NMC hereby further
     certifies that all of the Products purchased hereunder shall be for the
     exclusive use of treating dialysis patients.

10. AUTHORIZED WHOLESALERS.  A complete list of NMC's and Affiliates' current
    Authorized Wholesalers, through which NMC and Affiliates may purchase
    Products hereunder is attached as Appendix C. NMC and Affiliates agree to
    promptly provide Amgen with any additions, deletions, or changes to the
    initial list of Authorized Wholesalers. Amgen requires no less than thirty
    (30) days notice before the effective date of change for any addition or
    deletion by NMC of Authorized Wholesalers hereunder. Any proposed changes by
    NMC to the initial list of Authorized Wholesalers must be in writing by NMC
    and are subject to reasonable approval by Amgen.

11. SUBSIDIARIES AND AFFILIATES.  Attached as Appendix B is a current listing of
    all Affiliates, and other entities, that will be participating in this
    Agreement, designating which affiliates are owned and/or managed by
                                        2
<PAGE>

    NMC. Affiliates listed in Appendix B, as so designated by NMC and approved
    by Amgen, will be deemed "Affiliates" for the purposes of this Agreement.
    Subsequent to approval and acceptance by Amgen, a list of Affiliates shall
    be attached to this Agreement as Appendix B and incorporated herein. Only
    those Affiliates approved by Amgen and referenced in Appendix B will be
    eligible to participate under this Agreement. Any NMC managed Affiliate, or
    other entity with an existing contract, may participate in either their
    existing agreement with Amgen, or this Agreement, but not both. Each managed
    Affiliate or entity must declare under which single Amgen contract it will
    participate. Only Qualified Purchases under this Agreement will be used in
    the calculation of pricing, discounts or other incentives under this
    Agreement. NMC will notify Amgen monthly of changes to Appendix B., and the
    effective date of change. Such effective date of change may not be earlier
    than the date the notice is received by Amgen. Any proposed change to
    Appendix B will be subject to the reasonable approval of Amgen based upon
    Amgen's then current legal and contractual requirements, and such proposed
    Affiliate's classification as a freestanding dialysis center or a home
    dialysis support facility.

12. TERMINATION.  If either party materially breaches this Agreement the other
    party may terminate this Agreement upon thirty (30) days advance written
    notice specifying the breach, provided that such breach remains uncured at
    the end of the thirty (30) day period unless such breach is in violation of
    state, federal, or other applicable laws. In the event that NMC materially
    breaches any provision of this Agreement and the breach remains uncured for
    thirty (30) days following Amgen's notice of such breach, Amgen shall have
    no obligation to continue to offer the terms described herein or pay any
    further unvested discounts to NMC. However, any rebates or discounts that
    have been earned and vested at the time of termination shall still be paid
    pursuant to the applicable terms of Appendix A.

13. CONFIDENTIALITY.  Both Amgen and NMC agree that this Agreement represents
    and contains confidential information which will not be disclosed to any
    third party, or otherwise made public, without prior written authorization
    of the other party, except where such disclosure is contemplated hereunder
    or required by law or court order.  In the event NMC believes it is
    obligated to disclose any such information as required by law or court
    order, NMC will provide Amgen with prior written notice and an opportunity
    to seek a protective order and NMC shall furnish only that portion of the
    information that its counsel advises is required to be disclosed by law.
    Amgen acknowledges and agrees that NMC may file this Agreement as an exhibit
    to its parents' periodic reports to the Securities and Exchange Commission.

14. WARRANTIES.  Each party represents and warrants to the other that this
    Agreement (a) has been duly authorized, executed, and delivered by it, (b)
    constitutes a valid, legal, and binding agreement enforceable against it in
    accordance with the terms contained herein, and (c) does not conflict with
    or violate any of its of the contractual obligations, expressed or implied,
    to which it is a party or by which it may be bound. The party executing this
    Agreement on behalf of NMC specifically warrants and represents to Amgen
    that it is authorized to execute this Agreement on behalf of and has the
    power to bind NMC and the Affiliates to the terms set forth in this
    Agreement. The parties executing this on behalf of Amgen and Amgen Inc.
    specifically warrant and represent to NMC that they are authorized to
    execute this Agreement on behalf of and have the power to bind Amgen and
    Amgen Inc. to the terms set forth in this Agreement. Amgen warrants that the
    Products purchased pursuant to this Agreement (a) are manufactured and
    labeled in accordance with all applicable federal, state and local laws and
    regulations pertaining to the manufacturing of the Products including
    without limitation, the Federal Food, Drug, and Cosmetic Act and
    implementing regulations, and meet all specifications for effectiveness and
    reliability as required by the United States Food and Drug Administration,
    and (b) when used in accordance with the directions on the labeling, are fit
    for the purposes and indications described in the labeling. Amgen agrees
    that it will promptly notify NMC once it determines that there has been any
    material defect in any of the Products delivered to NMC.

15. GOVERNING LAW.  This Agreement will be governed by the laws of the State of
    Delaware and the parties submit to the jurisdiction of Delaware courts, both
    state and federal.

                                        3
<PAGE>

16. NOTICES.  Any notice or other communication required or permitted hereunder
    (excluding purchase orders) shall be in writing and shall be deemed given or
    made five (5) days after deposit in the United States mail with proper
    postage for first-class registered or certified mail prepaid, return receipt
    requested, or when delivered personally or by facsimile (Receipt verified
    and confirmed by overnight mail), or one (1) day following traceable
    delivery to a nationally recognized overnight delivery service with
    instructions for overnight delivery, in each case addressed to the parties
    as follows (or at such other addresses as the parties may notify each other
    in writing):

     If to NMC:

       Fresenius Medical Care Holdings, Inc.
        95 Hayden Avenue
        Lexington, MA 02420
        Attn: Robert McGorty, Senior Vice President
       Fax: 781-402-9718

     with a copy to:

       Fresenius Medical Care Holdings, Inc.
        95 Hayden Avenue
        Lexington, MA 02420
        Attn: General Counsel
       Fax: (781) 402-9713

     If to Amgen:

       Amgen USA Inc.
        One Amgen Center Drive, M/S 37-2-B
        Thousand Oaks, CA 91320-1789
        Attn: Gail Gilbotowski, Manager, Contract Administration
       Fax: (805) 447-8554

     with a copy to:

       Amgen USA Inc.
        One Amgen Center Drive, M/S 27-4-A
        Thousand Oaks, CA 91320-1789
        Attn: General Counsel
       Fax: (805) 447-1000

     If to Amgen, Inc.:

       Amgen Inc.
        One Amgen Center Drive, M/S 37-2-B
        Thousand Oaks, CA 91320-1789
        Attn: Gail Gilbotowski, Manager, Contract Administration
       Fax: (805) 447-8554

     with a copy to:

       Amgen Inc.
        One Amgen Center Drive, M/S 27-4-A
        Thousand Oaks, CA 91320-1789
        Attn: General Counsel
        Fax: (805) 447-1000

17. COMPLIANCE WITH HEALTH CARE PRICING AND PATIENT PRIVACY LEGISLATION AND
    STATUTES; DATA USE AGREEMENT.  (a) Notwithstanding anything contained herein
    to the contrary, at any time following the enactment of any federal, state,
    or local law, regulation, rule or interpretation that materially reforms,

                                        4
<PAGE>

    modifies, alters, restricts, or otherwise affects the pricing of or
    reimbursement available for any of the Products and/or results in material
    increase in Aranesp usage in dialysis clinics in the United States,
    including a reimbursement or use decision by Centers for Medicare and
    Medicaid Services ("CMS"), either party may initiate good faith negotiations
    to modify this Agreement as necessary. If the parties, after thirty (30)
    days, are unable to agree upon such a modification, (i) either party may
    terminate this Agreement immediately or (ii) Amgen may exclude any owned or
    managed Affiliate(s) from participating in this Agreement unless such owned
    or managed Affiliate(s) certifies in writing that they are, or will be,
    exempt from the provisions of such enacted law, regulation, rule or
    interpretation. Additionally, in order to assure compliance with any
    existing federal, state or local statute, regulation or ordinance, Amgen
    reserves the right, in its reasonable discretion, to exclude any owned or
    managed Affiliates from the pricing, discount, and incentive provisions of
    this Agreement. In the event there is a future change in Medicare, Medicaid,
    or other federal or state statutes or regulations or in the interpretation
    thereof, which renders any of the material terms of this Agreement unlawful
    or unenforceable, this Agreement shall continue only if amended by the
    parties as a result of good faith negotiations as necessary to bring the
    Agreement into compliance with such statute and regulation.

     (b) Notwithstanding anything contained herein to the contrary, in order to
     assure compliance, as determined by either party in its reasonable
     discretion, with any existing federal, state or local statute, regulation
     or ordinance relating to patient privacy of medical records, or at any time
     following the enactment of any federal, state, or local law or regulation
     relating to patient privacy of medical records that in any manner reforms,
     modifies, alters, restricts, or otherwise affects any of the data received
     or to be received in connection with any of the incentives contemplated
     under this Agreement, either party may upon thirty (30) days' notice, seek
     to modify this Agreement. NMC and Amgen shall meet and in good faith seek
     to mutually agree to modify this Agreement to accommodate any such change
     in law or regulation, [*]. If the parties in good faith determine that such
     modification is not possible, the parties shall seek to modify the
     Agreement in another manner acceptable to both parties. If the parties,
     after a reasonable time, are unable to agree upon such a modification,
     Amgen shall be entitled to terminate the affected incentive upon thirty
     (30) days' notice or upon the date such change in law or regulation goes
     into effect, whichever is earlier. [*].

     Notwithstanding anything contained herein to the contrary, this Agreement
     is effective only as of the date the parties hereto execute a mutually
     agreeable Data Use Agreement pursuant to which NMC may disclose a Limited
     Data Set of patient information to Amgen (as specified in the Data Use
     Agreement and which shall include, at a minimum, the data fields to be
     received by Amgen in connection with this Agreement) for purposes of
     Amgen's Research and Public Health analyses and NMC Health Care Operations.
     Unless otherwise specifically defined in this Agreement, each capitalized
     term used in this Section 17(c) shall have the meaning assigned to such
     term by the Health Insurance Portability and Accountability Act codified
     under 45 C.F.R. parts 160 and 164 ("HIPAA"). If NMC terminates the Data Use
     Agreement for any reason, Amgen shall be entitled to terminate the
     incentives described in Appendix A.

18. INSURANCE AND INDEMNITY.  During the Term of this Agreement, Amgen shall
    insure coverage of its obligations hereunder consistent with Amgen corporate
    policy through such programs of self-insurance and/or policies of general
    liability insurance through third-party carriers as Amgen shall determine in
    its sole discretion. Amgen agrees to indemnify, defend and hold harmless NMC
    and its Affiliates and their respective employees, officers and directors
    from and against any and all liabilities, losses, claims, or costs,
    including reasonable attorneys' fees, which result directly from Product
    which as of the date of shipment by Amgen: (i) contain defects in material
    and workmanship, (ii) are adulterated or misbranded within the meaning of
    applicable provisions of the Federal Food, Drug and Cosmetic Act (the "FDC
    Act"), or (iii) are prohibited from being introduced into interstate
    commerce by Section 301 of the FDC Act or Section 351 of the Public Health
    Service Act; provided that such indemnity shall not apply to claims arising
    out of the negligent or willful actions or omissions of NMC or its agents,
    employees, representatives, successors or assigns or due to defects in the
    Product caused by persons other than Amgen which result from neglect,
    misuse, unauthorized adulteration or modification, improper testing,
    handling or storage or any cause beyond the range of normal usage; and
    further provided that (a) Amgen is promptly notified in writing of any such
    claim, (b) Amgen shall have sole control of the defense and settlement
    thereof, and (c) NMC

                                        5
<PAGE>

    reasonably cooperates and gives Amgen all requested information and
    reasonable assistance for such defense. Notwithstanding the foregoing, Amgen
    shall not be liable for loss of profit or loss of use, incidental or
    consequential damages arising out of any claim asserted by NMC under this
    Agreement or otherwise. This paragraph sets forth NMC's sole indemnity
    remedy for claims of Product defect, adulteration or misbranding.

19. [*]

20. DIRECT PURCHASE OF PRODUCTS.  NMC may purchase EPOGEN(R) M20, 20,000U, 1mL
    vials, NDC 55513-478-10 packaged as ten (10) vials per pack and four (4)
    packs per case; S4, 4,000U, 1mL vials, NDC 55513-148-10 packaged as ten (10)
    vials per pack and ten (10) packs per case; and Aranesp? 25 mcg, 1.0 mL
    vials, NDC 55513-010-04 packaged as four (4) vials per pack and ten (10)
    packs per case; 40 mcg, 1.0 mL vials, NDC 55513-011-04 packaged as four (4)
    vials per pack and ten (10) packs per case; 60 mcg, 1.0 mL vials, NDC
    55513-012-04 packaged as four (4) vials per pack and ten (10) packs per
    case; 100 mcg, 1.0 mL vials, NDC 55513-013-04 packaged as four (4) vials per
    pack and ten (10) packs per case; 200 mcg, 1.0 mL vials, NDC 55513-014-01
    packaged as one (1) vial per pack and four (4) packs per case; 150mcg,
    0.75mL single-use vials, NDC 55513-054-04 packaged as four (4) vials per
    pack and ten (10) packs per case; 300mcg, 1.0mL single-use vials, NDC
    55513-015-01 packaged as one (1) vial per pack and four (4) packs per case;
    Aranesp(R) SingleJect(R) Prefilled Syringe 60 mcg, 0.3 mL (200 mcg/mL),
    single-use syringe, NDC 55513-039-04 packaged as 4 syringes per pack; 10
    packs per case; Aranesp(R) SingleJect(R) Prefilled Syringe 100 mcg, 0.5 mL
    (200 mcg/mL), single-use syringe, NDC 55513-041-04 packaged as 4 syringes
    per pack; 10 packs per case; Aranesp(R) SingleJect(R) Prefilled Syringe 200
    mcg, 0.4 mL (500 mcg/mL), single-use syringe, NDC 55513-044-01, packaged as
    1 syringe per pack; 4 packs per case; and Aranesp(R) SingleJect(R) Prefilled
    Syringe 300 mcg, 0.6 mL (500 mcg/mL), single-use syringe, NDC 55513-046-01,
    packaged as 1 syringe per pack; 4 packs per case (the "Direct Product") on a
    direct basis from Amgen in accordance with the terms set forth in Appendix D
    which is incorporated herein by reference.

21. DATA COLLECTION.  NMC agrees all data to be provided to Amgen pursuant to
    this Agreement shall be in a form that does not disclose the identity of any
    patient or any other patient-identifying information such as name, address,
    telephone number, birth date, all or part of a social security number,
    medical record number or prescription number. NMC and Amgen agree to use and
    accept only those patient identifiers compliant with HIPAA. Amgen and NMC
    acknowledge and agree that the data to be supplied to Amgen pursuant to this
    Agreement shall be used by Amgen solely to support verification of the
    discounts and incentives referenced herein, as well as for Amgen-sponsored
    research concerning the role of EPOGEN(R) in improving treatment outcomes
    and quality of life of dialysis patients. Notwithstanding the foregoing or
    any other provision of this Agreement, Amgen shall not obtain hereby any
    legal title to any NMC data and shall not sell or sublicense any data
    obtained hereunder. Any use by Amgen of such data shall be in a format that
    will not identify NMC or any Affiliates as the source of such data. NMC
    shall consistently use a unique alpha-numeric code (which shall not be the
    same as part or all of the patient's social security number) as a "case
    identifier" to track the care rendered to each individual patient over time,
    and such case identifier shall be included in the data provided to Amgen.
    The key or list matching patient identities to their unique case identifiers
    shall not be provided to Amgen personnel. In furtherance of Amgen research,
    NMC may agree from time to time to use its key to update the patient care
    data by linking it with information concerning health outcomes, quality of
    life, and other pertinent data that may become available to Amgen from other
    sources. Any such linking of data sources shall not provide the identity of
    any patient to Amgen. Amgen agrees it will maintain data supplied under this
    Agreement in confidence and it will not use such data to identify or contact
    any patient. No reports by Amgen concerning analyses of the data or the
    results of such research shall disclose the identity of any patient. Nothing
    in this Agreement shall limit NMC's use of its patient data, including
    without limitation, any data to be supplied to Amgen hereunder. For purposes
    of this Agreement, including Appendix A, NMC shall only be obligated to
    provide Amgen data with respect to its "Permanent" patients, as such term is
    defined in NMC's database. Generally, Permanent patients are those patients
    for whom NMC is the primary provider of dialysis services.

22. ACCESS.  Amgen and NMC agree that it and its agents and employees shall, at
    all times, comply with all applicable laws and regulations.
                                        6
<PAGE>

23. MISCELLANEOUS.  No modification of this Agreement shall be effective unless
    mutually agreed upon, made in writing and signed by a duly authorized
    representative of each party. This Agreement constitutes the entire
    agreement of the parties pertaining to the subject matter hereof and
    supersedes all prior written and oral agreements and understandings
    pertaining hereto including without limitation, any previous or existing
    contract, amendment, or agreement for the purchase of Products for use in
    the treatment of dialysis patients. Neither party shall have the right to
    assign this Agreement to a third party without the prior written consent of
    the other party provided, however, that Amgen may assign this Agreement to
    any of its subsidiaries or affiliates without the written consent of NMC.
    Neither party shall be liable for delays in performance and nonperformance
    of this Agreement or any covenant contained herein caused by fire, flood,
    storm, earthquake or other act of God, war, terrorist acts, rebellion, riot,
    failure of carriers to furnish transportation, strike, lockout or other
    labor disturbances, act of government authority, inability to obtain
    material or equipment, or any other cause of like or different nature beyond
    the control of such party. The parties shall execute and deliver all
    documents, provide all information, and take or refrain from taking action
    as may be necessary or appropriate to achieve the purposes of this
    Agreement. This Agreement may be executed in one or more counterparts, each
    of which is deemed to be an original but all of which taken together
    constitutes one and the same agreement. Upon expiration or early termination
    of this Agreement, the rights and obligations set forth in Sections 5, 6, 7,
    13,14, 18 and 22 shall survive such expiration or termination. In the event
    that the outcomes data proves to not serve and yield the beneficial results
    intended by both parties, Amgen and NMC will agree to meet, and negotiate in
    good faith.

24. PRODUCT INTEGRITY.  Amgen and NMC shall reasonably cooperate with each other
    in connection with each party's efforts to ensure the genuineness and
    integrity of Products purchased hereunder.

     Please retain one fully executed original for your records and return the
other fully executed original to Amgen.

THE PARTIES EXECUTED THIS AGREEMENT AS OF THE DATES SET FORTH BELOW.

<Table>
<S>          <C>
AMGEN USA INC.
Signature:   /s/ RICHARD W. REESE
Print Name:  Richard W. Reese
Print        Associate Director
Title:
Date:        12/23/03
AMGEN INC.
Signature:   /s/ HELEN TORLEY
Print Name:  Helen Torley
Print        Vice President -- General Mgr.
Title:
Date:        1/6/04
NATIONAL MEDICAL CARE, INC.
Signature:   /s/ ROBERT J. MCGORTY
Print Name:  Robert J. McGorty
Print        Vice President Finance and
Title:       Administration
Date:        12/23/03
</Table>

                                        7
<PAGE>

                                 APPENDIX A [*]

                                        8
<PAGE>

              APPENDIX B: LIST OF NMC SUBSIDIARIES AND AFFILIATES

                                 SUBSIDIARIES:

       Bio-Medical Applications Management Co., Inc. and its subsidiaries

                        Dialysis America, Georgia, LLC.

                                  Erika, Inc.

                   Integrated Renal Care of the Pacific, LLC.
                         Renal Research Institute, LLC.

                 SRC Holding Company, Inc. and its subsidiaries

             Everest Healthcare Holdings, Inc. and its subsidiaries

                         The Extracorporeal AllianceLLC

             Fresenius Medical Care Cardiovascular Resources, Inc.

                 Fresenius Medical Care Pharmacy Services, Inc.

                       Fresenius USA Manufacturing, Inc.
                         d/b/a Nephromed and affiliates

                                  AFFILIATES:

                           See Contract List Attached

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                                 APPENDIX C [*]

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                APPENDIX D: TERMS FOR PURCHASE OF DIRECT PRODUCT

     Pursuant to Section 20 of the Agreement, the terms under which NMC may
purchase Direct Product on a direct basis from Amgen are as follows:

1.   ORDERS/INVOICES.  NMC shall place Direct Product orders with NMC
     Distribution Center. NMC Distribution Center shall transmit orders and
     receive corresponding invoices via electronic data interchange ("EDI") in a
     format specified by Amgen.

     Orders may be submitted via facsimile, mail, or telephone to the address
     and telephone/fax numbers listed below. [*]

     Amgen Customer Service may be reached at the following address and phone
     numbers:

       Amgen USA Inc.
        Customer Service Department Fax: 1-800-292-6436
        One Amgen Center Drive Tel: 1-800-282-6436
       Thousand Oaks, CA 91320-1799

2.   SHIPPING, TRANSPORTATION AND CHARGES.  [*]

3.   TITLE AND RISK OF LOSS.  [*]

4.   PRICING FOR DIRECT PRODUCT.  [*]

5.   TERMS OF PAYMENT.  NMC Distribution Center agrees to pay [*] for Direct
     Product ordered, at terms of [*].

6.   CREDIT.  NMC Distribution Center shall send annually, within one hundred
     twenty (120) days of Fresenius Medical Care Holdings, Inc.'s ("FMCH")
     fiscal year end, or more frequently as requested by Amgen, copies of FMCH's
     audited financial statements for such fiscal year to:

       Amgen USA Inc.
        Customer Finance Department
        One Amgen Center Drive
       Thousand Oaks, CA 91320-1799

     If no audited financial statements are available, NMC Distribution Center
     shall send unaudited financial statements which are certified by NMC
     Distribution Center's principal financial officer as being accurate in all
     material respects. Amgen shall not be obligated to ship Direct Product to
     NMC Distribution Center if there are any amounts past due on NMC
     Distribution Center's account or if NMC Distribution Center's outstanding
     balance due exceeds NMC Distribution Center's predetermined credit limit.
     NMC Distribution Center shall supply Amgen written notice of the sale or
     transfer of all or substantially all of its assets of, or a controlling
     interest in, NMC Distribution Center at least thirty (30) days prior to
     such action if not otherwise prohibited by law or contractual obligations.
     Amgen reserves the right in its sole discretion to modify its credit
     policies and to require prepayment or satisfactory security at any time.

7.   SALES DATA.  NMC Distribution Center shall submit all Direct Product sales
     data, including Customer returns, rebillings and associated credits to IMS
     America, Ltd. ("IMS") and to any other third-party sales reporting
     organization as reasonably requested by Amgen, on a monthly basis, and
     within two (2) weeks after the close of each month. NMC Distribution Center
     shall provide all information and assistance reasonably required by Amgen
     to determine and verify Medicaid, other government, or third-party rebate
     claims or obligations. If NMC Distribution Center is unable to report such
     sales data to the agreed upon independent third-party sales reporting
     organization(s) due to unwillingness of the third party to deal with NMC
     Distribution Center, Amgen's sole recourse shall be to terminate the Direct
     Product purchase components of this Agreement.

8.   CONTRACTS AND CHARGEBACKS.  NMC Distribution Center agrees to service
     contracts that Amgen has entered into with Customers in accordance with the
     terms specified in bid award notifications sent by Amgen to NMC
     Distribution Center. [*]. Adjustments or credits will be made in accordance
     with Amgen's

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     Chargeback Policy (See Article One) attached hereto and incorporated
     herein. NMC Distribution Center further agrees to submit chargebacks to
     Amgen via EDI in a format acceptable to Amgen at least once per week, and
     in accordance with Amgen's Chargeback Policy. NMC Distribution Center shall
     retain all documentation supporting such chargebacks for a period of
     eighteen (18) months from the date of sale and permit Amgen employees or
     contractors (who shall not be compensated by Amgen on a contingency basis)
     to review this documentation upon request.

9.   PRODUCT RETURNS.  NMC Distribution Center shall comply with Amgen's Product
     Return Policy (See Article Two) and all requirements of the Prescription
     Drug Marketing Act of 1987 (as amended from time to time).

     a. Returns by Customer to NMC Distribution Center

     NMC Distribution Center shall notify Amgen of all Direct Product returned
     to NMC Distribution Center in the form of a negative chargeback. This will
     ensure that the proper adjustment is made to NMC Distribution Center's
     account.

     b. Returns by NMC Distribution Center to Amgen

     Amgen shall only accept Direct Product returns from NMC Distribution Center
     that have been pre-authorized by Amgen Customer Service. Direct Product
     must be in original, unopened and undamaged cartons and returned within
     twelve (12) months post expiration and must be in full compliance with
     Amgen's Product Return Policy (See Article Two) attached hereto and
     incorporated herein. Amgen will promptly issue credit to NMC Distribution
     Center in accordance with Amgen's Product Return Policy.

     c. Returns by Customer to Amgen

     Amgen shall accept from Customer Direct Product returns that have been
     pre-authorized by Amgen Customer Service. NMC Distribution Center agrees to
     promptly issue credit to Customer returning Direct Product directly to
     Amgen and for which Amgen has issued a credit memo to NMC Distribution
     Center.

10. REBILLINGS AND ASSOCIATED CREDITS.  NMC Distribution Center agrees to submit
    to Amgen all Customer rebillings and associated credits in conformance with
    Amgen's Chargeback Policy.

11. PRODUCT RECALL.  In the event of a recall, Amgen will promptly notify NMC
    Distribution Center and relevant Customer of such recall and arrange for
    Direct Product to be shipped directly to Amgen. Amgen will provide a
    third-party billing number (common carrier) to Customer and NMC Distribution
    Center for shipping of recalled Direct Product directly to Amgen. NMC
    Distribution Center shall provide a list of Customer names and addresses to
    Amgen who may have received recalled Direct Product. In consideration for
    NMC Distribution Center's administrative expenses, Amgen will pay NMC
    Distribution Center for a list of each Customer that may have received
    recalled Direct Product in the amount equal to $1.00 per Customer name up to
    a maximum $100.00 per distribution center. NMC Distribution Center shall
    render its services and assist Amgen in returning all recalled Direct
    Product to Amgen. Amgen shall provide reasonable compensation to NMC
    Distribution Center per HDMA standards for additional services that may be
    requested by Amgen. A credit memo will be issued to NMC Distribution Center
    for all recalled Direct Product returned to Amgen. NMC Distribution Center
    shall promptly issue credit to Customer for recalled Direct Product returned
    directly to Amgen for which Amgen has issued a credit memoranda to NMC
    Distribution Center. NMC Distribution Center may call Amgen Customer Service
    at 1-800-282-6436 for further instructions in the event of a recall.

12. APPLICABLE LAWS AND REGULATIONS.  Amgen and NMC Distribution Center agree to
    comply with all laws (local, state and federal) applicable to the purchase,
    handling, sale, and distribution of Direct Product. NMC agrees to provide
    Amgen with the statutory citation of all local and state laws and
    regulations contemplated by this Section 12. In the event there shall be a
    change in federal or state statutes (including, but not limited to Medicare
    or Medicaid statutes, Federal Food, Drug and Cosmetic Act (the "FDC Act"),
    and any other statutes governing distribution, handling, purchasing, or sale
    of drugs, medical supplies and durable medical

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<PAGE>

    equipment), case laws, regulations or general instructions, the
    interpretation of any of the foregoing, the adoption of new federal or state
    legislation, or a change in any third party reimbursement system, any of
    which are reasonably likely to materially and adversely affect the manner in
    which either party may perform or be compensated for its services under this
    Agreement or which shall make this Agreement unlawful, the parties shall
    immediately enter into good faith negotiations regarding a new service
    arrangement or basis for compensation for the services furnished pursuant to
    this Agreement that complies with the law, regulation, or policy. If good
    faith negotiations cannot resolve the matter within thirty (30) days, the
    parties shall terminate the Agreement.

13. DIVERSION.  NMC Distribution Center shall distribute Direct Product only to
    those approved Subsidiaries and Affiliates listed on Exhibit B. NMC
    Distribution Center shall promptly notify Amgen upon learning of any
    activity that appears to be diversion of Direct Product, including the sale,
    distribution or purchase of Direct Product for uses beyond the provision of
    care for dialysis patients, or the sale or distribution of Direct Product
    outside of the United States and Puerto Rico. Amgen may terminate this
    Agreement upon written notice if it is determined by Amgen, in its sole
    discretion, that NMC Distribution Center has purchased Direct Product from
    sources other than Amgen or distributed Direct Product to entities not
    listed on Exhibit B.

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<PAGE>

               APPENDIX E: LIST OF APPROVED DISTRIBUTION CENTERS

Fresenius USA Manufacturing, Inc.
d/b/a Nephromed and affiliates
95 Hayden Avenue
Lexington, MA 92420-9192

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<PAGE>

                                  ARTICLE ONE

CHARGEBACK POLICY

1.   INITIAL SUBMISSIONS:

     Chargeback claims must be submitted via EDI in a format acceptable to
     Amgen. Claims must be received by Amgen no later than sixty (60) calendar
     days after NMC Distribution Center has invoiced the Customer. Each item
     must contain the information necessary to uniquely identify the Customer,
     including the Health Industry Number (HIN) and complete ship-to name and
     address, or other identifier as required by Amgen.

2.   PROCESSING TIME:

     Amgen will process all initial chargeback claims received in an acceptable
     format within ten (10) business days. Once the chargeback claim has been
     processed, NMC Distribution Center will receive, by mail, the credit
     memoranda and/or discrepancy report.

3.   DISCREPANCIES:

     PARTIAL REJECTIONS:  If any item cannot be validated from the claim, it
     will be rejected and credit will not be issued for that item. NMC
     Distribution Center will receive the credit memoranda for the validated
     items in conjunction with the discrepancy report for rejected items. A
     reason will be given for each rejected item.

     FULL REJECTIONS:  Submissions not in an acceptable format or with a
     rejection rate greater than ten percent (10%) may be rejected in full. Upon
     such notification, NMC Distribution Center must correct the error(s) and
     electronically retransmit the entire claim.

4.   RESUBMISSIONS:

     Amgen will accept resubmissions for rejected chargebacks within sixty (60)
     calendar days after NMC Distribution Center has been notified of the
     rejection. Claims must be submitted on Amgen's discrepancy report with any
     corrections or additional information necessary to validate such claim.

5.   CUSTOMER RETURNS:

     NMC Distribution Center must report its Customer returns as "negative" or
     "reverse" chargebacks.

6.   CREDITS AND REBILLS:

     NMC Distribution Center shall submit simultaneously to Amgen the credits
     and their associated rebills within sixty (60) calendar days after NMC
     Distribution Center rebills a Customer.

7.   CONTRACT ELIGIBILITY:

     Claims will only be honored for sales made in accordance with the Bid Award
     Notifications sent by Amgen to NMC Distribution Center. A facility may only
     participate on one (1) contract for each product at any given time. An
     individual contract will take precedence over any group purchasing
     organization contract of which the facility may be a part.

8.   AUDIT:

     Amgen shall have access to all information necessary to verify chargeback
     claims.

9.   DEDUCTIONS:

     Deductions of chargeback claims are not permitted unless supported with a
     valid credit memoranda from Amgen.

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<PAGE>

     Amgen's Chargeback Policy conforms with the guidelines set by the
Healthcare Distribution Management Association. Amgen reserves the right to
modify its Chargeback Policy upon notice to NMC pursuant to Section 16 in the
Agreement.

                                  ARTICLE TWO

PRODUCT RETURN POLICY

AUTHORIZATION:

     Contact Amgen Customer Service Department at 800-282-6436 for proper
instructions and procedures for returning Direct Product.

RETURNABLE ITEMS:

     -  Expired Direct Product in full pack quantity with less than one-year
        post expiration date.

     -  Direct Product received in error or damaged in transit.

NON-REFUNDABLE ITEMS: Although all Direct Product may be returned, no credit
will be issued for:

     -  Direct Product twelve (12) months or more post expiration date.

     -  Direct Product destroyed or damaged due to improper storage, heat, cold,
        water, and smoke, left out of refrigeration or other conditions beyond
        the control of Amgen.

     -  Direct Product destroyed or losses suffered in a natural disaster
        (flood, hurricane, tornado, etc.).

     -  Direct Product obtained other than through normal channels of
        distribution.

     -  Direct Product that is in unsaleable condition through no fault of
        Amgen.

     -  Direct Product shipped as a "no charge" item.

     -  Unauthorized excess stock.

TRANSPORTATION CHARGES:

     -  Prepaid by Customer

TERMS OF RETURN POLICY:

     -  Credit, if applicable, for outdated Direct Product, will be based on
        current price less fifteen percent (15%).

     -  No credit for shipping, handling and return processing fees.

     -  Amgen will not be responsible for any charges associated with third
        party return processors.

     -  Pre-authorized excess stock returns will be credited at eighty percent
        (80%) of the original purchase price.

     -  Direct Product ordered or received in error must be reported within ten
        (10) business days of Direct Product receipt.

     -  Credit for indirect Customer, for outdated Direct Product, will be
        issued in the form of a check by Capital Returns Inc. on behalf of
        Amgen.

     -  Credit for direct Customer, for outdated Direct Product, will be issued
        by Amgen in the form of a credit invoice.

     -  Unauthorized deductions from invoices are not allowed.

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     -  All items are subject to credit approval by Amgen Customer Service.

THIRD PARTY RETURN PROCESSORS:

     -  For all outdated Direct Product, please forward return with detail
        manifest directly to:

       Capital Returns, Inc.
        Attn: Amgen Return Goods
        406 North Port Washington Road
        Milwaukee, WI 53212

COMPANY DISCLAIMER:

     -  Direct Product returned is subject to Amgen's and or Capital Returns'
        evaluation at the time of receipt for final count and inspection.

     -  Amgen may, in its sole discretion, make exceptions, changes and/or
        modifications to Returned Goods Policy.

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<PAGE>

                                                                      EXHIBIT #1

                          SAMPLE CERTIFICATION LETTER

Month X, 2004

FSDC Legal Name
Street Address
City, ST Zip

RE: Agreement No. ____________

Dear ____________ :

     Thank you for your participation in the [*] program. In order for us to
enroll you, we require that a duly authorized representative of your
organization sign the certification below.

     Upon receipt of this executed document, we will calculate the value of your
incentive. If we do not receive the executed certification, we cannot provide
you with this incentive.

     If you have any questions regarding this letter please contact me at [*].
Thank you for your assistance in returning this certification.

Sincerely,

---------------------------------------------------------
[*]

CERTIFICATION:

     On behalf of FSDC Legal Name and all eligible Affiliates participating in
the [*] program under Agreement No.          , the undersigned hereby certifies
that the data submitted for each eligible Affiliate includes the required
results from all dialysis patients of such Affiliate, and does not include
results from non-patients. The party executing this document also represents and
warrants that it (i) has no reason to believe that the submitted data is
incorrect, and (ii) is authorized to make this certification on behalf of all
eligible Affiliates submitting data.

FSDC LEGAL NAME

<Table>
<S>            <C>
Signature:     ---------------------------------------------
Print Name:    ---------------------------------------------
Print          ---------------------------------------------
Title:
Date:          ---------------------------------------------
</Table>

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