Document:

<PAGE>   1
                                                                    EXHIBIT 10.4

                                            The deleted portions of this Exhibit
                                                contain confidential information
                                         and have been filed separately with the
                                              Securities and Exchange Commission

                     Amendment #2 dated March 27, 2000 to Agreement No. 19984813

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

Agreement No. 19984813, between Amgen Inc. ("Amgen") and National Medical Care,
Inc., including any prior amendments thereto, shall be amended, and for the
period commencing 1/1/2000 shall be restated in its entirety to read as stated
below.

This Agreement ("Agreement"), between Amgen Inc. ("Amgen") and National Medical
Care, Inc., including its subsidiaries and affiliates that are at least fifty
and one-tenth percent (50.10%) owned by National Medical Care, Inc. listed on
Appendix B, (collectively, "NMC"), sets forth the terms and conditions for the
purchase of EPOGEN(R) (Epoetin alfa) by NMC.

1.   TERM OF AGREEMENT. The "Term" of this Agreement shall be defined as January
     1, 2000 ("Commencement Date") through December 31, 2000 ("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 13, to all affiliates 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. ("Affiliates"), 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 13, Affiliates of Renaissance Health Care, Clinic, Inc.,
     Optimal Renal Care, L.L.C., Integrated Renal Care of the Pacific, 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. 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 EPOGEN(R) through an Authorized
     Wholesaler or from Amgen directly.

5.   PRODUCT ACQUISITION COSTS. As long as NMC and Affiliates are the [DELETED],
     non-governmental, freestanding dialysis center (including home dialysis
     affiliates) purchaser of EPOGEN(R) in the United States, Puerto Rico and
     Guam during the Term, on an annual, calendar year basis, Amgen commits that
     this Agreement provides NMC and Affiliates with [DELETED] for EPOGEN(R)
     available to any freestanding dialysis center purchaser in the United
     States and Puerto Rico with comparable growth and percentage of patients
     with hematocrit levels greater than or equal to [DELETED]. If NMC and
     Affiliates are not the [DELETED] non-governmental, freestanding dialysis
     center purchaser of EPOGEN(R) in the United States, Puerto Rico and Guam
     during the Term, on a calendar year basis, Amgen may provide [DELETED] for
     EPOGEN(R) to [DELETED] non-governmental, freestanding dialysis center
     purchaser(s). Qualification as a freestanding dialysis center shall be
     determined by Amgen in its reasonable discretion, in accordance with
     Amgen's customer classification policies, which generally classify
     freestanding dialysis centers as independent, exclusive providers of
     dialysis services, which (a) may not obtain EPOGEN(R) from or through a
     hospital, or (b) are not otherwise affiliated with a hospital, nursing
     home, or integrated health care system. This commitment excludes [DELETED]
     available to any governmental entities, or [DELETED] mandated by Title 38
     (Veterans' Benefits) or Title 42 (The Public Health and Welfare) of the
     United States Code, or any other federal or state health care program.
     Amgen's agreement to make this commitment is contingent upon its ability to
     comply with all federal, state, local and military laws, statutes and
     regulations.

6.   MINIMUM PRODUCT PURCHASE AGREEMENT. NMC and Affiliates agree to purchase a
     minimum of [DELETED] of EPOGEN(R) from Amgen hereunder during each
     consecutive calendar quarter during the Term.

<PAGE>   2
7.   DISCOUNT. Amgen will pay discounts and incentives in accordance with the
     schedule and terms set forth in Appendix A attached hereto.

8.   PAYMENT OF DISCOUNTS. Any discount (hereinafter defined as including a
     discount at time of purchase, rebate, incentive or other concession
     impacting the pricing of a product) earned hereunder shall be calculated in
     accordance with this Agreement, based on Qualified Purchases, using
     [DELETED] as the calculation price, and shall be paid in the form of a wire
     transfer to NMC's corporate headquarters, except as otherwise provided. 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. Amgen shall make available to NMC any records concerning NMC's and
     Affiliates' purchase amounts that NMC or its auditors may reasonably
     request. [DELETED] 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 EPOGEN(R) 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 EPOGEN(R)
     distributed by NMC or Affiliates to non-Affiliates of NMC (see Section 2
     for definition of Affiliates). Subject to the section entitled "Breach of
     Agreement", 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 which may have been
     earned hereunder prior to the effective date of the acquisition shall
     vest, and shall be paid in the form of a wire transfer to NMC's corporate
     headquarters subject to the conditions described herein.

9.   TREATMENT OF DISCOUNTS. The parties agree that they will account for any
     discount 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
     (a) claim the benefit of such discount received, in whatever form, in the
     fiscal year in which such discount was earned or the year after, (b) 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 (c) 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
     to account for any such discount in accordance with the above stated
     requirements.

10.  COMMITMENT TO PURCHASE. NMC and Affiliates agrees to purchase EPOGEN(R) for
     all of its dialysis use requirements in the United States, Puerto Rico and
     Guam for recombinant human erythropoietin. Amgen agrees to make such
     EPOGEN(R) available to NMC and Affiliates through its Authorized
     Wholesalers or directly from Amgen. In addition to other remedies available
     to NMC and Affiliates, NMC and Affiliates may purchase another brand of
     recombinant human erythropoietin for its dialysis use requirements in the
     United States, Puerto Rico and Guam if, and only if, NMC and Affiliates
     have informed Amgen, in writing, that NMC and Affiliates are unable to
     acquire sufficient amounts of EPOGEN(R) to meet NMC's and Affiliates'
     reasonable dialysis use requirements, and Amgen by itself, or through its
     Authorized Wholesalers, is actually unable to supply NMC and Affiliates
     with their reasonable dialysis use requirements of EPOGEN(R) within the
     time period reasonably required by NMC and Affiliates, which, in no event
     will be less than five (5) business days after Amgen's receipt of NMC's and
     Affiliates' written notice. If the preceding requirements are met, NMC and
     Affiliates will only be allowed to purchase another brand of recombinant
     human erythropoietin for the time period, and to the extent, that Amgen is
     unable to provide NMC and Affiliates with EPOGEN(R) to meet NMC's and
     Affiliates' reasonable dialysis use requirements.

11.  OWN USE. NMC hereby certifies that EPOGEN(R) purchased hereunder will be
     for the "own use" by NMC and the Affiliates of NMC.

12.  AUTHORIZED WHOLESALERS. A complete list of NMC's and Affiliates' current
     Authorized Wholesalers, through whom NMC and Affiliates may purchase
     EPOGEN(R) hereunder is attached as Appendix C. NMC and Affiliates agrees to
     promptly

<PAGE>   3
     provide Amgen with any additions, deletions, or changes to the initial list
     of Authorized Wholesalers. Amgen requires no less than 30 days notice
     before the effective date of change for any addition or deletion of
     Authorized Wholesalers hereunder. Any proposed changes to the initial list
     of Authorized Wholesalers must be in writing and are subject to reasonable
     approval by Amgen.

13.  SUBSIDIARIES AND AFFILIATES. Within 30 days of execution of this Agreement,
     NMC shall provide 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 NMC. Such listing will be incorporated into
     this Agreement as Appendix B. Only those entities listed on Appendix B will
     be eligible to participate in 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 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.

14.  BREACH OF AGREEMENT. Either party may terminate this Agreement for a
     material breach upon thirty (30) days advance written notice provided such
     breach remains uncured at the end of the thirty (30) day period.

15.  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.

16.  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 other contractual obligations, expressed or implied,
     to which it is a party or by which it may be bound. NMC represents and
     warrants that it has the power to bind National Medical Care, Inc. and the
     subsidiaries and owned Affiliates listed on Appendix B to the terms
     contained herein. NMC shall cause each managed Affiliate to be bound by the
     terms and conditions of this Agreement through the execution of a joinder
     agreement executed between NMC and each such managed Affiliate.

17.  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.

18.  NOTICES. Any notice or other communication required or permitted hereunder
     will be in writing and shall be deemed given or made when delivered in
     person or when received by the other party sent by U.S. Mail, return
     receipt requested, at the respective party's address set forth below or at
     such other address as the party shall have furnished to the other in
     accordance with this provision.

19.  COMPLIANCE WITH HEALTH CARE PRICING LEGISLATION AND STATUTES.
     Notwithstanding anything contained herein to the contrary, at any time
     following the enactment of any federal, state, or local law or regulation
     that materially reforms, modifies, alters, restricts, or otherwise affects
     the pricing of or reimbursement available for EPOGEN(R), either party may
     initiate good faith negotiations to modify this Agreement. If after
     forty-five (45) days the parties are unable to in good faith mutually agree
     to modifications to this Agreement, (a) either party may terminate this
     Agreement immediately, or (b) Amgen may exclude any owned or managed
     Affiliates 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 or

<PAGE>   4
     regulation. 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 and shall be amended by the
     parties as a result of good faith negotiations as necessary to bring the
     Agreement into compliance with such statute and regulation.

20.  MISCELLANEOUS. No modification of this Agreement shall be effective unless
     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 or amendment for the purchase
     of EPOGEN(R). Neither party shall have the right to assign this Agreement
     to a third party without the prior written consent of the other party.
     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, 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. However, during any time of nonperformance by Amgen
     which involves NMC's and Affiliates' inability to obtain sufficient
     EPOGEN(R) to meet NMC's and Affiliates' reasonable dialysis use
     requirements the [DELETED] for such nonperformance, the [DELETED] and NMC
     and Affiliates may purchase EPOGEN(R) from another supplier. 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. Amgen reserves
     the right to rescind this offer if the parties fail to execute this
     Agreement within thirty (30) days from the date of its offering.

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

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

AMGEN INC.                             NATIONAL MEDICAL CARE, INC.

Signature:     \s\ Eric Benevich      Signature:     \s\ Robert J. McGorty
Print Name:    Eric Benevich          Print Name:    Robert J. McGorty
Print Title:   Product Manager        Print Title:   Vice President of
                                                     Finance and Administration
Date:          3/29/00                Date:          3/29/00

<PAGE>   5

                APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS
                -------------------------------------------------

1.   PRICING. NMC and Affiliates may purchase EPOGEN(R) directly from Amgen or
     through Authorized Wholesalers at a [DELETED]. Resulting prices do not
     include any wholesaler markup, service fees, or other charges.

2.   [DELETED] NMC and Affiliates agree to provide [DELETED] for the purposes of
     calculating [DELETED]. Amgen will accept the [DELETED] multiply each
     [DELETED] by [DELETED] and apply the converted results to [DELETED].
     [DELETED] Amgen will accept electronic data from the lab systems that
     service each owned or managed Affiliate. For NMC to qualify for the
     [DELETED] the following requirements must be met:

A.       REQUIREMENTS: In order to participate in the [DELETED] NMC and
         Affiliates must provide the following information for each dialysis
         patient to Amgen or to a data collection vendor specified by Amgen, on
         a [DELETED] basis, no later than [DELETED] after the end of [DELETED]:*

         i)       facility ID, [DELETED] [DELETED] for EPOGEN(R), [DELETED],
                  treatment date, [DELETED], [DELETED], [DELETED], [DELETED],
                  [DELETED], EPOGEN(R) dose (collectively the "Data"). Amgen may
                  utilize the Data for any purpose, and reserves the right to
                  audit all Data. Notwithstanding the foregoing, Amgen shall not
                  sell or re-sell any Data obtained pursuant to this Agreement.
                  Additionally, any use by Amgen of such Data shall be in a
                  format that does not identify NMC as the source of such Data,
                  unless NMC has consented to such use. Under no circumstances
                  should the Data include any patient identifiable information
                  including, without limitation, name, complete social security
                  number, address or birth date. The identity of the account
                  submitting the Data and any association with the Data will
                  remain confidential and will not be used in a manner that is
                  patient identifiable. The [DELETED] must be derived from
                  [DELETED] taken immediately before dialysis treatment using
                  any automated [DELETED] testing method (e.g [DELETED]) must be
                  reported to the [DELETED], and must be submitted in a format
                  acceptable to Amgen. Hand written reports are not acceptable;
                  electronic submission of the Data is preferred; and

         ii)      [DELETED] and

         iii)     a properly executed "Annual Certification Letter", a sample of
                  which is attached hereto as Exhibit #1, that will be provided
                  to NMC's corporate headquarters, unless otherwise requested,
                  after this Agreement is executed by both parties.

         *NOTWITHSTANDING THE REQUIREMENT TO SUBMIT DATA ON A [DELETED] BASIS
REFERENCED ABOVE, THE [DELETED] DATA ELEMENTS REFERENCED IN 2a ii) ABOVE SHALL
BE REQUIRED FOR THE [DELETED] WITHIN [DELETED] DAYS FOLLOWING THE END OF THE
[DELETED]. COMMENCING WITH THE [DELETED] OF [DELETED], THE DATA ELEMENTS SET
FORTH IN 2a ii) SHALL BE REQUIRED ON A [DELETED] BASIS AS SET FORTH IN THIS
SECTION 2A.

B.       CALCULATION: Assuming NMC and Affiliates have fulfilled all
         requirements as described in Section 2(a) above, NMC's [DELETED]
         payment will be calculated as follows: The "Average Patient [DELETED] "
         for each dialysis patient will be based upon the average of all
         [DELETED] gathered for each patient during each [DELETED] of the Term.
         The [DELETED] of all dialysis patients with Average Patient [DELETED]
         greater than or equal to [DELETED] will be determined by dividing the
         total number of dialysis patients with Average Patient [DELETED]
         greater than or equal to [DELETED] by the total number of dialysis
         patients treated by NMC and Affiliates. The [DELETED] will be
         calculated based on NMC's and Affiliates' overall performance in
         accordance with Amgen's discount calculation policies.

<PAGE>   6
          APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS (CONTINUED)
          -------------------------------------------------------------

C.       PAYMENT: The [DELETED] will be calculated on a [DELETED] and paid to
         NMC's corporate headquarters, except as otherwise provided hereunder.
         Payment is contingent upon receipt by Amgen of the Annual Certification
         Letter (attached hereto as Exhibit 1) and all required Data for the
         corresponding [DELETED]. Data shall be submitted to Amgen [DELETED] and
         no later than [DELETED]. If Data is [DELETED], NMC will not qualify for
         the [DELETED] for that [DELETED]. [DELETED]. However, if Amgen
         determines that any Affiliate(s) is consistently not submitting the
         required Data, Amgen reserves the right in its reasonable discretion to
         exclude such Affiliate's Qualified Purchases of EPOGEN(R)from the
         calculation of the [DELETED] for any relevant [DELETED]. [DELETED]
         payments will be based on the Data received from the [DELETED], and
         will equal a percentage of NMC's and Affiliates' total Qualified
         Purchases of EPOGEN(R) during each relevant [DELETED] (exclusive of any
         Qualified Purchases of EPOGEN(R) made by NMC or any Affiliate not
         meeting the Data submission requirements described above) as governed
         by the [DELETED] schedules listed below. Amgen reserves the right to
         modify the [DELETED] if the EPOGEN(R) package insert language changes.
         [DELETED].

<PAGE>   7
          APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS (CONTINUED)
          -------------------------------------------------------------

                    [DELETED] INCENTIVE [DELETED] SCHEDULES:

         [DELETED]

         [DELETED]

D.       VESTING: The [DELETED] will vest on the [DELETED] and be paid in
         accordance with the terms and conditions of Section 2 c) Payment above.
<PAGE>   8

          APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS (CONTINUED)

3.       [DELETED]: NMC shall be eligible to receive a [DELETED] if certain data
         elements are transmitted to Amgen [DELETED]. The [DELETED] will be
         calculated as a percentage of Qualified Purchases of
         EPOGEN(R) attributable to NMC and all Affiliates during each [DELETED]
         In order to qualify for the [DELETED], the following [DELETED] must be
         submitted by NMC and all Affiliates in an [DELETED] format reasonably
         acceptable to Amgen[DELETED] Facility ID, [DELETED] [DELETED],
         [DELETED] for EPOGEN(R), [DELETED], treatment date, [DELETED],
         [DELETED], [DELETED], [DELETED], calculated [DELETED], EPOGEN(R) dose,
         [DELETED], and [DELETED]. Such [DELETED] must be submitted on a
         [DELETED] basis, and no later than [DELETED]. If such [DELETED] is
         received more than [DELETED], NMC will not qualify for the [DELETED]
         for that [DELETED]. [DELETED] However, if Amgen determines that any
         Affiliate(s) is consistently not submitting the required [DELETED]
         Amgen reserves the right in its sole discretion to exclude such
         Affiliate's Qualified Purchases of EPOGEN(R) from the calculation of
         the [DELETED] for any relevant [DELETED]. [DELETED]

4.       [DELETED] NMC may qualify for the [DELETED] as described below.

         A.    CALCULATION: NMC's [DELETED] will be calculated in accordance
               with the following formula and with each relevant [DELETED]
               schedule listed below:

                                [DELETED] = A X B

         where
                  A = [DELETED].
                  B = [DELETED]
                  C = [DELETED]
                  D = [DELETED]

<PAGE>   9

          APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS (CONTINUED)
          -------------------------------------------------------------

                    [DELETED] INCENTIVE [DELETED] SCHEDULES:

                                    [DELETED]

         [DELETED]
         (C-D)/D                                             B
         -------                                             -
         [DELETED]

                                    [DELETED]

         [DELETED]
         (C-D)/D                                             B
         -------                                             -
         [DELETED]

                                    [DELETED]

         [DELETED]
         (C-D)/D                                             B
         -------                                             -
         [DELETED]

                                    [DELETED]

         [DELETED]
         (C-D)/D                                             B
         -------                                             -
         [DELETED]

<PAGE>   10

          APPENDIX A: DISCOUNT PRICING, SCHEDULE, AND TERMS (CONTINUED)
          -------------------------------------------------------------

For the purposes of calculating [DELETED], Amgen will incorporate purchases of
any newly created facility (but not facilities added through acquisition).
[DELETED]

B.   VESTING: NMC's [DELETED] will vest on the [DELETED], and will be paid in
     accordance with the terms and conditions described above.

5.   [DELETED]. NMC may qualify for the [DELETED] as described below.

A.   CALCULATION: NMC's [DELETED] will be calculated in accordance with the
     following formula and in accordance with the [DELETED] schedule listed
     below.

                                [DELETED] = A X B
         where
                A =  [DELETED].
                B =  [DELETED].
                C =  [DELETED].
                D =  [DELETED].

         [DELETED]
         (C-D)/D                                            B
         -------                                            -
         [DELETED]

B.   VESTING: NMC's [DELETED] will vest on the last day of the Term, and will be
     paid [DELETED] thereafter.

<PAGE>   11

               APPENDIX B: LIST OF NMC SUBSIDIARIES AND AFFILIATES
               ---------------------------------------------------

                                  SUBSIDIARIES:
                                  -------------

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

                                   Erika, Inc.

                               Infusion Care, Inc.

                                 LifeChem, Inc.

                  National Medical Care HomeCare Division, Inc.

                         Renal Research Institute, Inc.

                            Spectra Renal Management

                                   AFFILIATES:
                                   -----------

                           See Contract List Attached

<PAGE>   12

                 APPENDIX C: LIST OF NMC AUTHORIZED WHOLESALERS
                 ----------------------------------------------

TO ENSURE YOU RECEIVE THE APPROPRIATE DISCOUNT, IT IS IMPORTANT THAT WE HAVE
YOUR CURRENT LIST OF AUTHORIZED WHOLESALERS. THE FOLLOWING LIST REPRESENTS THE
WHOLESALERS AMGEN CURRENTLY HAS ASSOCIATED WITH YOUR CONTRACT. PLEASE UPDATE THE
LIST BY ADDING OR DELETING WHOLESALERS AS NECESSARY.

Bergen Brunswig Corporation
4000 Metropolitan Drive
Orange, CA  92668

J.M. Blanco Inc.
Calle D - Lote No. 21
Guaynabo, PR 00965

Metro Medical Supply, Inc.
3332 Powell Avenue
Nashville, TN 37204

Bellco Drug Corporation
101 East Hoffman Avenue
Lindenhurst, NY 11757

<PAGE>   13

                                                                      EXHIBIT #1

                       SAMPLE ANNUAL CERTIFICATION LETTER
                       ----------------------------------

Month X, 199X

FSDC Legal Name
Street Address
City, ST  Zip

RE:  EPOGEN(R)(Epoetin alfa) Agreement No. 19984813

Dear ____________:

Thank you for your participation in the [DELETED] Incentive 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 [DELETED].
Thank you for your assistance in returning this certification.

Sincerely,

[DELETED]
Outcomes Incentive Analyst

CERTIFICATION:

On behalf of FSDC Legal Name and all eligible Affiliates participating in the
[DELETED] Incentive Program under Agreement No. 19984813, the undersigned hereby
certifies that the [DELETED] data submitted for each eligible Affiliate includes
the required [DELETED] results from all dialysis patients of such Affiliate, and
does not include [DELETED] results from non-patients. The party executing this
document also represents and warrants that it (i) has no reason to believe that
the submitted [DELETED] data is incorrect, and (ii) is authorized to make this
certification on behalf of all eligible Affiliates submitting [DELETED] data.

FSDC LEGAL NAME

Signature:
              --------------------------
Print Name:
              --------------------------

Print Title:
              --------------------------

Date:
              --------------------------<PAGE>   1
                                                                   EXHIBIT 10.15

                              EMPLOYMENT AGREEMENT

THIS AGREEMENT, is made and entered into this 15th day of March, 2000, by and
between Fresenius Medical Care North America ("FMC" or the "EMPLOYER"), with
principal offices located at 95 Hayden Avenue, Lexington, MA 02420 and Jerry A.
Schneider ( "EMPLOYEE") currently residing at 44 Kings Grant Road, Weston, MA
02493.

WITNESSETH:

WHEREAS, FMC desires to employ EMPLOYEE as Chief Financial Officer at FMC and
its affiliated corporations in North America, and

WHEREAS, the parties hereto desire to express the terms and conditions of such
employment.

NOW THEREFORE, it is understood and agreed to between the parties as follows:

1.   EMPLOYMENT. FMC hereby employs EMPLOYEE as Chief Financial Officer, and
     EMPLOYEE hereby accepts the employment upon the terms and conditions of
     this Agreement.

2.   TERM. The term of this Agreement shall commence as of March 15, 2000 and
     shall terminate as of March 15, 2003 in accordance with the provisions
     hereinafter stated. THE INITIAL TERM SHALL BE RENEWED BY A SUCCESSIVE THREE
     (3) YEAR PERIOD UNLESS EITHER PARTY GIVES WRITTEN NOTICE OF NON-RENEWAL TO
     THE OTHER PARTY AT LEAST THIRTY (30) DAYS PRIOR TO ANY TERMINATION DATE.
     THE INITIAL TERM AND ANY SUBSEQUENT RENEWAL PERIODS SHALL BE CALLED THE
     "EMPLOYMENT TERM."

3.   DUTIES AND RESPONSIBILITIES. EMPLOYEE shall serve full time as FMC's Chief
     Financial Officer and will be responsible for all financial functions,
     including debt management, bank relationships and human resources. EMPLOYEE
     shall report directly to the Chief Executive Officer of FMC and shall also
     report to the Chief Financial Officer of Fresenius AG on debt management
     and investor relations issues. EMPLOYEE shall to the best of his ability
     and experience competently, loyally, diligently and conscientiously perform
     all of the duties and obligations expressly or implicitly required under
     this Agreement. EMPLOYEE further agrees that, in conducting business in the
     interest of the EMPLOYER, he will not engage in, knowingly permit others
     under his control to carry on, or induce others to engage in any practice
     or commit any acts in violation of any federal or state or local law or
     ordinance.

4.   COMPENSATION AND BENEFITS.

a)   BASE SALARY. EMPLOYER shall pay EMPLOYEE for all services rendered a base
     salary of Three Hundred Seventy Two Thousand, Six Hundred Dollars
     ($372,600) per year, (the "Base Salary"), payable in accordance with FMC's
     payroll procedures, subject to customary withholding and employment taxes.
     At the end of each year of employment hereunder, EMPLOYEE's performance for
     the prior year shall be reviewed and evaluated. If EMPLOYEE's performance
     is satisfactory, EMPLOYEE shall receive an increase in his base salary
     commensurate with level of achievement.

b)   INCENTIVE COMPENSATION. During EMPLOYEE's employment with FMC, EMPLOYEE
     shall be entitled to participate in FMC's Management Bonus Plan and any
     other such incentive compensation plans as are now available or may become
     available to other similarly positioned senior executives of FMC. EMPLOYEE
     will be in the senior executive eligibility Level I, wherein the target
     level bonus is forty percent (40%) and the maximum bonus is eighty percent
     (80%) of base salary. Funding for the plan is based upon attainment of
     specific individual and company financial objectives. EMPLOYEE's
     entitlement to a bonus under the Management Bonus Plan will be governed by
     terms of that Plan.

<PAGE>   2

c)   STOCK PLAN. EMPLOYEE shall be eligible to participate in the current
     Fresenius Medical Care AG Stock Incentive Plan, and any future stock
     incentive plan (individually a "Stock Plan" and collectively, the "Stock
     Plans"), subject to IRS approval of such respective Stock Plans. In
     addition to the existing options to purchase Fresenius Medical Care AG
     Preference Shares previously granted to EMPLOYEE (the "Existing Options"),
     EMPLOYEE shall be eligible to receive additional option grants in amounts
     as and if approved by the Fresenius Medical Care AG Managing Board.

d)   BENEFIT PROGRAMS. EMPLOYEE shall continue to be eligible to participate in
     the group employee benefits programs at the senior executive level as now
     established or which subsequently become available.

e)   LIFE INSURANCE. EMPLOYEE will be provided with life insurance in accordance
     with FMC's policy, currently capped at Four Hundred Thousand Dollars
     ($400,000). EMPLOYEE will be provided with the opportunity to purchase
     supplemental life insurance of an additional Six Hundred Thousand Dollars
     ($600,000) beyond the current policy of coverage at his own expense, with
     proof of good health.

f)   AUTOMOBILE. EMPLOYEE will be provided with a company car allowance of Seven
     Hundred Dollars ($700) paid monthly and treated as ordinary income.

g)   FINANCIAL PLANNING/TAX PREPARATION. EMPLOYEE will be provided with an
     allowance of Two Thousand Dollars ($2,000) to be paid based upon submitted
     documentation of expenses incurred as a result of financial planning
     assistance or income tax preparation. Reimbursement will be treated as
     ordinary income.

h)   EXPENSES. EMPLOYEE will be reimbursed for travel and other expenses related
     to the performance of his duties under the Agreement and in accordance with
     the EMPLOYER's policies.

i)    VACATION/PTO. EMPLOYEE shall be allowed to carry-over up to two hundred
      (200) hours from year-to-year without losing such time. EMPLOYEE shall
      also accrue PTO days at the maximum available to senior executives under
      the Executive Vacation Policy which currently provides for thirty (30)
      days of PTO per year.

5.   TERMINATION OF EMPLOYMENT. EMPLOYEE's employment hereunder may be
     terminated under the following circumstances:

a)   DEATH. EMPLOYEE's employment hereunder shall terminate upon his death.

b)   TOTAL DISABILITY. The EMPLOYER may terminate EMPLOYEE's employment
     hereunder upon EMPLOYEE becoming "Totally Disabled." For purposes of this
     Agreement, EMPLOYEE shall be "Totally Disabled" if EMPLOYEE is physically
     or mentally incapacitated so as to render EMPLOYEE incapable of performing
     EMPLOYEE's usual and customary duties under this Agreement. EMPLOYEE's
     receipt of Social Security disability benefits or disability benefits under
     a Company-sponsored long-term disability plan shall be deemed conclusive
     evidence of Total Disability for purpose of this Agreement; provided,
     however, that in the absence of EMPLOYEE's receipt of such Social Security
     or long-term disability benefits, the Company's Board of Directors may, in
     its reasonable discretion (but based upon medical evidence), determine that
     EMPLOYEE is Totally Disabled.

c)   VOLUNTARY TERMINATION. EMPLOYER or EMPLOYEE may terminate EMPLOYEE's
     employment hereunder at any time after providing written notice to the
     other party. The EMPLOYEE is required to give the EMPLOYER at least thirty
     (30) days written notice if he wishes to terminate his employment pursuant
     to this provision.

d)   TERMINATION BY THE EMPLOYER FOR CAUSE. The EMPLOYER may terminate
     EMPLOYEE's employment for Cause at any time after providing written notice
     to EMPLOYEE. For purposes of this Agreement, the term "Cause" shall mean,
     with respect to the EMPLOYEE, any of the following: (i) commission by
     EMPLOYEE of a felony or of any criminal act involving moral turpitude which
     results in an arrest or indictment; (ii) deliberate and continual refusal
     to satisfactorily perform employment duties reasonably requested by the
     EMPLOYER
                                        2
<PAGE>   3

     after 20 days' written notice by certified mail of such failure to perform,
     specifying that the failure constitutes cause (other than as a result of
     vacation, sickness, illness or injury); (iii) fraud or embezzlement
     determined in accordance with the EMPLOYER's normal, internal investigative
     procedures consistently applied in comparable circumstances to EMPLOYEES;
     (iv) gross misconduct or gross negligence in connection with the business
     of the EMPLOYER which has substantial effect on the EMPLOYER; (v) failure
     to obtain and maintain in good order any licenses required for EMPLOYEE to
     perform his duties under this Agreement; or (vi) a breach of any of the
     covenants set forth in Section 7 below. EMPLOYEE will be considered to have
     been terminated for "Cause" if the EMPLOYER determines that EMPLOYEE
     engaged in an act constituting "Cause," regardless of whether the
     individual terminates employment voluntarily or is terminated
     involuntarily, and regardless of whether the individual's termination
     initially was considered to have been for "Cause." The determination of
     "Cause" shall be made by the EMPLOYER in its sole discretion, and shall be
     final and binding on all parties.

e)   TERMINATION BY EMPLOYEE FOR CAUSE. This Agreement may be terminated by
     EMPLOYEE in the event of a breach by FMC of any of its obligations under
     this Agreement, provided EMPLOYEE gives FMC written notice specifying the
     manner in which he believes FMC has breached this Agreement and FMC has
     thirty (30) days from receipt of such notice to cure such breach, or in the
     case of other than a non-payment of money breach, if such breach cannot be
     cured within thirty (30) days, to commence a good faith effort to cure.

     Additionally, this Agreement may be terminated by Employee, if there is a
     reduction in Employee's responsibilities or FMC experiences a change in
     control defined as any of the following: i) the transfer (whether by sale,
     dividend, exchange, lease, merger, consolidation or otherwise) of greater
     that 50 percent (50%) of the voting power of FMC; ii) the transfer (whether
     by sale, dividend, exchange, lease, merger, consolidation or otherwise) of
     all or substantially all the assets or stock of FMC; or iii) any other
     action which results in persons other than the current majority
     shareholders of FMC, having the voting power to direct the management of
     FMC or if FMC relocates its corporate headquarters more than fifty (50)
     miles from its present location in Lexington, Massachusetts.

f)   NOTICE OF TERMINATION. Any termination by the EMPLOYER or the EMPLOYEE
     under this Agreement shall be communicated by notice of termination to the
     other party hereto. For purposes of this Agreement, a Notice of Termination
     shall mean a notice in writing which shall indicate the specific
     termination provision in this Agreement relied upon to terminate EMPLOYEE's
     employment and shall set forth in reasonable detail the facts and
     circumstances claimed to provide a basis for termination of EMPLOYEE's
     employment under the provision so indicated.

6.   COMPENSATION FOLLOWING TERMINATION OF EMPLOYMENT.

a)   Under all circumstances, upon termination the EMPLOYEE shall be entitled to
     receive:

            (i)   Any accrued but unpaid Base Salary for services rendered to
                  the date of termination; and

            (ii)  Any benefits to which EMPLOYEE may be entitled upon
                  termination pursuant to the plans, policies and arrangements
                  referred to in Section 4 hereof shall be determined and paid
                  in accordance with the terms of such plans, policies and
                  arrangements. ** EMPLOYEE shall have three (3) years from any
                  such termination to exercise his Vested Stock Options. Should
                  he fail to exercise these options within this period, they
                  will be forfeited at the end of that period.

b)   In the event that EMPLOYEE's employment hereunder is voluntarily terminated
     by the EMPLOYER in accordance with Section 5(c), or in the event that
     EMPLOYEE's employment hereunder is terminated by the EMPLOYEE in accordance
     with Section 5(e), the EMPLOYEE shall also be entitled to receive:

            (iii) The balance of the salary payments equivalent to the number of
                  months remaining in the term of the Employment Agreement. At a
                  minimum, the number of months for salary continuance would

                                       3
<PAGE>   4

                  be eighteen (18) at the rate in effect on the date of
                  termination of employment, such amount to be paid in a lump
                  sum as soon as is practicable thereafter; and

            (iv)  A pro-rated portion of the EMPLOYEE's annual bonus based upon
                  termination of work date.

c)   Any stock options or other awards will continue to vest in accordance with
     the terms of the award and the plan pursuant to which it was made. If the
     terms of any award and governing plan are silent with respect to
     termination of employment, such award will lapse immediately upon such
     termination.

7.   NON-DISCLOSURE/NON COMPETITION AGREEMENT. EMPLOYEE acknowledges that during
     the term of employment with EMPLOYER, he will have access to and become
     acquainted with Confidential Information of the EMPLOYER. Confidential
     Information means all information related to the present or planned
     business of FMC that has not been released publicly by authorized
     representatives of FMC, and shall include but not be limited to, trade
     secrets and know-how, inventions, marketing and sales programs, employee,
     customer, patient and supplier information, information from patient
     medical records, financial data, pricing information, regulatory approval
     and reimbursement strategies, data, operations and clinical manuals.

      EMPLOYEE agrees not to use or disclose, directly or indirectly, any
     Confidential Information of FMC at any time and in any manner, except as
     required in the course of his employment with FMC or with the express
     written authority of FMC.

     EMPLOYEE understands that his non-disclosure obligations will continue
     following his termination of employment.

     EMPLOYEE agrees that during the term of his employment, and for a period of
     one (1) year immediately after, he leaves the employment of FMC for any
     reason or the end of the period during which EMPLOYEE continues to receive
     salary continuation after leaving the employment of FMC, whichever is
     greater, EMPLOYEE will not directly or indirectly for his own benefit or
     the benefit of others:

          a)   render services for a competing organization in connection with
               competing products as an employee, officer, agent, broker,
               consultant, partner, stockholder (except that EMPLOYEE may own
               three percent (3%) or less of the equity securities of any
               publicly-traded company);

          b)   hire or seek to persuade any employee of FMC to discontinue
               employment or to become employed in any competing organization or
               seek to persuade any independent contractor or supplier to
               discontinue its relationship with FMC; and

          c)   solicit, direct, take away or attempt to take away any business
               or customers of FMC.

     Nothing in this Agreement would preclude EMPLOYEE from working for a
     competitor of FMC's subsequent to termination of EMPLOYEE's employment
     provided EMPLOYEE will not be engaged, directly or indirectly, in any
     business in which FMC is actively engaged at the time of EMPLOYEE's
     termination or in any new business which FMC is in the process of setting
     up in which EMPLOYEE had direct involvement while employed by FMC. EMPLOYEE
     also agrees to inform FMC of any such employment with a competitor before
     beginning such employment.

8.   ENFORCEMENT OF COVENANTS.

a)   TERMINATION OF EMPLOYMENT AND FORFEITURE OF COMPENSATION. EMPLOYEE agrees
     that in the event that the EMPLOYER determines that EMPLOYEE has breached
     any of the covenants set forth in Section 7 hereof during EMPLOYEE's
     employment, the EMPLOYER shall have the right to terminate EMPLOYEE's
     employment for "Cause." For purposes of this Agreement, the term "Cause"
     shall mean, with respect to the EMPLOYEE, any of the following: (i)
     commission by EMPLOYEE of a felony or of any criminal act involving moral
     turpitude which results in an arrest or indictment; (ii) deliberate and
     continual refusal to

                                       4
<PAGE>   5

     satisfactorily perform employment duties reasonably requested by the
     EMPLOYER after 20 days' written notice by certified mail of such failure to
     perform, specifying that the failure constitutes cause (other than as a
     result of vacation, sickness, illness or injury); (iii) fraud or
     embezzlement determined in accordance with the EMPLOYER's normal, internal
     investigative procedures consistently applied in comparable circumstances
     to EMPLOYEES; (iv) gross misconduct or gross negligence in connection with
     the business of the EMPLOYER which has substantial effect on the EMPLOYER;
     (v) failure to obtain and maintain in good order any licenses required for
     EMPLOYEE to perform his duties under this Agreement; or (vi) a breach of
     any of the covenants set forth in Section 7 above. EMPLOYEE will be
     considered to have been terminated for "Cause" if the EMPLOYER determines
     that EMPLOYEE engaged in an act constituting "Cause," regardless of whether
     the individual terminates employment voluntarily or is terminated
     involuntarily, and regardless of whether the individual's termination
     initially was considered to have been for "Cause." The determination of
     "Cause" shall be made by the EMPLOYER in its sole discretion, and shall be
     final and binding on all parties.

     In addition, EMPLOYEE agrees that if the EMPLOYER determines that EMPLOYEE
     has breached any of the covenants set forth in Section 7 at any time, the
     EMPLOYER shall have the right, notwithstanding anything herein to the
     contrary, to discontinue any or all amounts otherwise payable to EMPLOYEE
     hereunder. Such termination of employment or discontinuance of payments
     shall be in addition to and shall not limit any and all other rights and
     remedies that the EMPLOYER may have against EMPLOYEE.

b)   RIGHT TO INJUNCTION. EMPLOYEE acknowledges that a breach of the covenants
     set forth in Section 7 hereof will cause irreparable damage to the EMPLOYER
     with respect to which the EMPLOYER's remedy at law for damages will be
     inadequate. Therefore, in the event of breach or anticipatory breach of the
     covenants set forth in this section by EMPLOYEE, EMPLOYEE and the EMPLOYER
     agree that the EMPLOYER shall be entitled to the following particular forms
     of relief, in addition to remedies otherwise available to it at law or
     equity: (i) injunctions, both preliminary and permanent, enjoining or
     retraining such breach or anticipatory breach and EMPLOYEE hereby consents
     to the issuance thereof forthwith and without bond by any court of
     competent jurisdiction; and (ii) recovery of all reasonable sums expended
     and costs, including reasonable attorney's fees, incurred by the EMPLOYER
     to enforce the covenants set forth in this section.

c)   SEPARABILITY OF COVENANTS. The covenants contained in Section 7 hereof
     constitute a series of separate covenants, one for each applicable State in
     the United States and the District of Columbia, and one for each applicable
     foreign country. If in any judicial proceeding, a court shall hold that any
     of the covenants set forth in Section 7 exceed the time, geographic, or
     occupational limitations permitted by applicable laws, EMPLOYEE and the
     EMPLOYER agree that such provisions shall and are hereby reformed to the
     maximum time, geographic, or occupational limitations permitted by such
     laws. Further, in the event a court shall hold unenforceable any of the
     separate covenants deemed included herein, then such unenforceable covenant
     or covenants shall be deemed eliminated from the provisions of this
     Agreement for the purpose of such proceeding to the extent necessary to
     permit the remaining separate covenants to be enforced in such proceeding.
     EMPLOYEE and the EMPLOYER further agree that the covenants in Section 7
     shall each be construed as a separate agreement independent of any other
     provisions of this Agreement, and the existence of any claim or cause of
     action by Employee against the Company whether predicated on this Agreement
     or otherwise, shall not constitute a defense to the enforcement by the
     Company of any of the covenants in Section 7.

9.   FMC DOCUMENTS AND EQUIPMENT. All documents and equipment relating to the
     business of FMC, whether prepared by EMPLOYEE or otherwise coming into
     EMPLOYEE's possession, are the exclusive property of FMC, and must not be
     removed from the premises of FMC except as required in the course of
     employment. Any such documents and equipment must be returned to FMC when
     EMPLOYEE leaves the employment of FMC.

10.  WITHHOLDING OF TAXES. The EMPLOYER may withhold from any compensation and
     benefits payable under this Agreement all applicable federal, state, local,
     or other taxes.

                                       5
<PAGE>   6

11.  ENTIRE AGREEMENT AND AMENDMENTS. This Agreement shall constitute the entire
     agreement between the parties and supersedes all existing agreements
     between them, whether oral or written, with respect to the subject matter
     hereof. Any waiver, alteration, or modification of any of the provisions of
     this Agreement, or cancellation or replacement of this Agreement shall be
     accomplished in writing and signed by the respective parties.

12.  NOTICES. Any notice, consent, request or other communication made or given
     in connection with this Agreement shall be in writing and shall be deemed
     to have been duly given when delivered or mailed by registered or certified
     mail, return receipt requested, to those listed below at their following
     respective addresses or at such other address as each may specify by notice
     to the others:

                  To the Employer:

                        Fresenius Medical Care North America
                        Corporate Headquarters
                        Two Ledgemont Center
                        95 Hayden Avenue
                        Lexington, MA 02420-9192
                        Attention:  Vice President, Human Resources

                  To Employee:

                        At the address for Employee set forth above

13.  GOVERNING LAW. This Agreement shall be construed in accordance with, and
     the rights of the parties shall be governed by, the laws of the
     Commonwealth of Massachusetts.

14.  SEPARABILITY. If any term or provision of this Agreement is declared
     illegal or unenforceable by any court of competent jurisdiction and cannot
     be modified to be enforceable, such term or provision shall immediately
     become null and void, leaving the remainder of this Agreement in full force
     and effect.

IN WITNESS WHEREOF, the parties have caused this Agreement to be executed by the
undersigned duly authorized persons as of the day and year first stated above.

                                   NATIONAL MEDICAL, INC. D/B/A
                                   FRESENIUS MEDICAL CARE
                                   NORTH AMERICA,

WITNESS                            EMPLOYER

/s/ Brian O'Connell            By: /s/ Ben Lipps                         4/20/00
------------------------           -------------------------             -------
                                   Ben J. Lipps                           (DATE)
                                   Chief Executive Officer

WITNESS                            JERRY A. SCHNEIDER

/s/ Patricia Hanna                 /s/ Jerry A. Schneider                 4/3/00
------------------------           -------------------------              ------
                                   (Employee Signature)                   (DATE)

                                       6

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