<PAGE>   1


                                                                    EXHIBIT 10.2

                                 AMENDMENT NO. 4


         THIS AMENDMENT NO. 4, dated as of August 26, 1997 (the "AMENDMENT")
relating to the Credit Agreement referenced below, by and among NATIONAL MEDICAL
CARE, INC., a Delaware corporation, certain subsidiaries and affiliates party to
the Credit Agreement and identified on the signature pages hereto, and
NATIONSBANK, N.A., as Paying Agent for and on behalf of the Lenders. Terms used
but not otherwise defined shall have the meanings provided in the Credit
Agreement.

                               W I T N E S S E T H

         WHEREAS, a $2.5 billion credit facility has been extended to National
Medical Care, Inc. and certain subsidiaries and affiliates pursuant to the terms
of that Credit Agreement dated as of September 27, 1996 (as amended and
modified, the "CREDIT AGREEMENT") among National Medical Care, Inc., the other
Borrowers, Guarantors and the Lenders identified therein, and NationsBank, N.A.,
as Paying Agent;

         WHEREAS, the Company has made plans to refinance and replace its
existing $200 million receivables securitization program with a $204 million
receivables securitization program;

         WHEREAS, the Company has requested certain modifications described
herein in connection therewith which require the consent of the Required
Lenders; and

         WHEREAS, the Required Lenders have consented to the requested
modifications on the terms and conditions set forth herein and have authorized
the Paying Agent to enter into this Amendment on their behalf to give effect to
this Amendment;

         NOW, THEREFORE, IN CONSIDERATION of these premises and other good and
valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the parties hereto agree as follows:

         A. The Credit Agreement is amended and modified in the following 
respects:

                  1. The Managing Agents and the Required Lenders hereby consent
to the structure, terms and tenor of the proposed securitization transaction as
structured by NationsBanc Capital Markets, Inc. on the terms attached as
SCHEDULE 1.

                  2. The following definitions in Section 1.1 are amended or
added to read as follows:

                  "EXCLUDED SECURITIZATION TRANSACTION" means the accounts
         receivable financing facility of the Company contemplated by the Trade
         Receivables Purchase and Sale Agreement dated as of December 30, 1991
         among Bio-Medical Applications Management Co., Inc., as seller, and
         Ciesco, L.P., as investor, and Citicorp North America, Inc., as agent,
         as amended and supplemented, and any Permitted Receivables Financing
         entered into in replacement thereof, but only to the extent of
         $204,000,000 in aggregate Attributed Principal Amount (any greater
         amount being subject to the mandatory prepayment provisions of Section
         3.3(b)(iii) hereof).

                  "SECURITIZATION SUBSIDIARY" means a special purpose subsidiary
         or affiliate established in connection with a Permitted Receivables
         Financing.

                  3. The lead-in language in Section 7.11(a) is amended to read
as follows:

         "If a Domestic Subsidiary of NMC (and, if Holdings is a Guarantor, of
         Holdings), other than a Securitization Subsidiary, which is a Material
         Subsidiary is not a Credit Party hereunder, then the Company will
         promptly notify the Paying Agent thereof and cause such Material
         Subsidiary to become a Credit party hereunder by"

                  4. The reference in section 8.1(e) to "$200,000,000" is
increased and amended to read "$204,000,000".


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<PAGE>   2


         B. Except as modified hereby, all of the terms and provisions of the
Credit Agreement (and Exhibits and Schedules) remain in full force and effect.

         C. The Company agrees to pay all reasonable costs and expenses of the
Paying Agent in connection with the preparation, execution and delivery of this
Amendment, including without limitation the reasonable fees and expenses of
Moore & Van Allen, PLLC.

         D. This Amendment may be executed in any number of counterparts, each
of which when so executed and delivered shall be deemed an original and its
shall not be necessary in making proof of this Amendment to produce or account
for more than one such counterpart.

         E. This Amendment, and the Credit Agreement as amended hereby, shall be
governed by and construed and interpreted in accordance with the laws of the
State of New York.

                  [Remainder of Page Intentionally Left Blank]




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<PAGE>   3


         IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart
of this Amendment to be duly executed and delivered as of the date first above
written.

BORROWERS:                NATIONAL MEDICAL CARE, INC.,
                                   a Delaware corporation

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President

                                   FRESENIUS MEDICAL CARE AG

                                   By /s/ Gerd Krick
                                      ------------------------------------------
                                   Name:  Gerd Krick
                                   Title: Management Board Member

                                   By /s/ Udo Werle
                                      ------------------------------------------
                                   Name:  Udo Werle
                                   Title: Management Board Member

                                   NMC DO BRASIL LTDA.,
                                   a Brazil corporation

                                   By /s/ Joao Pedrinelli
                                      ------------------------------------------
                                   Name:  Joao Pedrinelli
                                   Title: General Manager

                                   NATIONAL MEDICAL CARE OF SPAIN, S.A.,
                                   a Spanish corporation

                                   By /s/ Dwight Morgan
                                      ------------------------------------------
                                   Name:  Dwight Morgan
                                   Title: Managing Director

                                   NATIONAL MEDICAL CARE OF TAIWAN, INC.,
                                   a Delaware corporation

                                   By /s/ Dwight Morgan
                                      ------------------------------------------
                                   Name:  Dwight Morgan
                                   Title: Managing Director




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<PAGE>   4



                                   NMC CENTRO MEDICO NACIONAL, LDA.,
                                   a Portuguese corporation

                                   By /s/ Dwight Morgan
                                      ------------------------------------------
                                   Name:  Dwight Morgan
                                   Title: Managing Director

                                   NMC DE ARGENTINA, S.A.,
                                   an Argentine corporation

                                   By /s/ Joao Pedrinelli
                                      ------------------------------------------
                                   Name:  Joao Pedrinelli
                                   Title: General Manager

                                   FRESENIUS USA, INC.,
                                   a Massachusetts corporation

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President

                                   FRESENIUS MEDICAL CARE DEUTSCHLAND GmbH,
                                   a German corporation

<TABLE>
                                   <S>                                                  <C>
                                   By /s/ Gerd Krick                                    By: /s/  Dietmar Blumenhagen
                                      ------------------------------------------            -----------------------------------
                                   Name:  Gerd Krick                                    Name:  Dietmar Blumenhagen
                                   Title: Chief Executive Officer                       Title: Treasurer

</TABLE>

                                   FRESENIUS MEDICAL CARE GROUPE FRANCE
                                   (formerly known as Fresenius Groupe
                                   France S.A.), a French corporation

                                   By /s/ Udo Werle
                                      ------------------------------------------
                                   Name:  Udo Werle
                                   Title: Board Member

                                   FRESENIUS MEDICAL CARE HOLDING, S.p.A.,
                                   an Italian corporation

                                   By /s/ E. Gatti
                                      ------------------------------------------
                                   Name:  E. Gatti
                                   Title: Board Member





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<PAGE>   5




                                   FRESENIUS MEDICAL CARE ESPANA S.A.,
                                   a Spanish corporation

                                   By /s/ E. Gatti
                                      ------------------------------------------
                                   Name:  E. Gatti
                                   Title: Board Member

                                   FRESENIUS MEDICAL CARE MAGYAROSZA KfG,
                                   a Hungarian corporation

                                   By /s/ N. Erhard
                                      ------------------------------------------
                                   Name:  N. Erhard
                                   Title: Board Member

PAYING AGENT:                      NATIONSBANK, N.A.,
                                   as Paying Agent for and on behalf of the 
                                   Lenders

                                   By /s/ Ashley M. Crabtree
                                      ------------------------------------------
                                            Ashley M. Crabtree
                                            Senior Vice President

GUARANTORS:               FRESENIUS NATIONAL MEDICAL CARE
                                   HOLDINGS, INC., a New York corporation 
                                   formerly known as WRG-NY

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President

                                   NATIONAL MEDICAL CARE, INC.,
                                   a Delaware corporation

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President

                                   BIO-MEDICAL APPLICATIONS MANAGEMENT CO.,
                                   INC., a Delaware corporation

                                   By /s/ Geoffrey W. Swett
                                      ------------------------------------------
                                   Name:  Geoffrey W. Swett
                                   Title: President



                                       44
<PAGE>   6



                                   NMC HOMECARE, INC.,
                                   a Delaware corporation

                                   By /s/ Michael J. Sicilian
                                      ------------------------------------------
                                   Name:  Michael J. Sicilian
                                   Title: Vice President

                                   LIFECHEM, INC.,
                                   a Delaware corporation

                                   By /s/ Geoffrey W. Swett
                                      ------------------------------------------
                                   Name:  Geoffrey W. Swett
                                   Title: President

                                   FRESENIUS MEDICAL CARE AG,
                                   a German corporation

<TABLE>
                                   <S>                                                  <C>
                                   By /s/ Gerd Krick                                    By: /s/ Dietmar Blumenhagen
                                      ------------------------------------------            ------------------------------------
                                   Name:  Gerd Krick                                    Name:  Dietmar Blumenhagen
                                   Title: Chief Executive Officer                       Title: Treasurer
</TABLE>

                                   FRESENIUS USA, INC.,
                                   a Massachusetts corporation

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President

                                   FRESENIUS MEDICAL CARE DEUTSCHLAND
                                   GmbH, a German corporation

<TABLE>
                                   <S>                                                  <C>
                                   By /s/ Gerd Krick                                    By: /s/ Dietmar Blumenhagen
                                      ------------------------------------------            ------------------------------------
                                   Name:  Gerd Krick                                    Name:  Dietmar Blumenhagen
                                   Title: Chief Executive Officer                       Title: Treasurer
</TABLE>

                                   FRESENIUS MEDICAL CARE GROUPE
                                   FRANCE, a French corporation
                                   (formerly known as Fresenius Groupe
                                   France S.A.)

                                   By /s/ Udo Werle
                                      ------------------------------------------
                                   Name:  Udo Werle
                                   Title: Board Member




                                       45
<PAGE>   7


                                   FRESENIUS SECURITIES, INC.,
                                   a California corporation

                                   By /s/ Ben Lipps
                                      ------------------------------------------
                                   Name:  Ben Lipps
                                   Title: President







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<PAGE>   8



                           CONSENT TO AMENDMENT NO. 4


NationsBank, N.A., as Paying Agent
101 N. Tryon Street, 15th Floor
NC1-001-15-04
Charlotte, North Carolina 28255
Attn:  Carol Lindsay, Agency Services

         Re:      Credit Agreement dated as of September 27, 1996 (as amended 
                  and modified, the "CREDIT AGREEMENT") among National Medical
                  Care, Inc., the other Borrowers, Guarantors and Lenders
                  identified therein and NationsBank, N.A., as Paying Agent.
                  Terms used but not otherwise defined shall have the meanings
                  provided in the Credit Agreement.

                  Amendment No. 4 dated August 26, 1997 (the "SUBJECT
                  AMENDMENT") relating to the Credit Agreement

Ladies and Gentlemen:

         This should serve to confirm our receipt of, and consent to, the
Subject Amendment. We hereby authorize and direct you, as Paying Agent for the
Lenders, to enter into the Subject Amendment on our behalf in accordance with
the terms of the Credit Agreement upon your receipt of such consent and
direction from the Required Lenders, and agree that Company and the other Credit
Parties may rely on such authorization.

                                         Sincerely,



                                         -----------------------------
                                                [Name of Lender]

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





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<PAGE>   9


                                   SCHEDULE 1

                    Description of Securitization Transaction


















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