<PAGE>   1


                                                                     EXHIBIT 4.8

                                 AMENDMENT NO. 6


     THIS AMENDMENT NO. 6, dated as of June 30, 1998 (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 Lenders identified therein, and NationsBank, N.A., as
Paying Agent;

     WHEREAS, the Company has requested the consent of the Paying Agent and
Lenders to (i) the assumption by FMC Trust Finance S.a.r.l. Luxembourg, a
limited liability company organized under the laws of Luxembourg ("FMC TRUST
FINANCE"), or a successor thereof, of the obligations of Holdings with respect
to the 9% Senior Subordinated Notes due December 1, 2006 (the "1996 SUBORDINATED
NOTES") issued to evidence the loans made to Holdings of the proceeds from the
issuance by the FMC Trust of the preferred securities referred to in the
definition of "Refinancing Securities" and the common securities of the FMC
Trust contemplated by clause (xvi) of the definition of Permitted Investments,
(ii) the guaranty by Holdings of the obligations of FMC Trust Finance or its
successor under the 1996 Subordinated Notes and (iii) certain related changes to
the terms of the 1996 Subordinated Notes, the FMC Trust and the related
documentation, which assumption, guaranty and other changes have already been
approved by the holders of the Refinancing Securities;

     WHEREAS, the Company has requested certain other changes to the Credit
Agreement more fully set forth herein;

     WHEREAS, the requested consents and modifications described herein 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:

<PAGE>   2


          1.   The Managing Agents and Required Lenders hereby consent to the
     modification of the Refinancing Securities to permit (i) the assumption by
     FMC Trust Finance S.a.r.l. Luxembourg, a limited liability company
     organized under the laws of Luxembourg and a wholly-owned subsidiary of
     Holdings, of the obligations of Holdings with respect to the 1996
     Subordinated Notes, (ii) the guaranty by Holdings of the obligations under
     the 1996 Subordinated Notes, (iii) the adoption of provisions which,
     subject to the provisions of the Credit Agreement, would permit Holdings or
     any wholly-owned subsidiary of Holdings (other than the Company and its
     Subsidiaries) to assume the obligations of the note issuer thereunder, and
     (iv) certain related changes to the terms of the 1996 Subordinated Notes,
     the FMC Trust and the related documentation, a description of which is
     attached as Exhibit A attached hereto, or such other form not materially
     adverse to the interests of the Lenders, and waive compliance with any
     provisions of the Credit Agreement to the extent that such modification
     would conflict with such provisions.

          2.   In Section 1.1,

          (a)  The following definitions are hereby amended or added to read as
          follows:

                    "Refinancing Securities" means (i) the $360,000,000
               Aggregate Liquidation Amount of 9% Trust Preferred Securities Due
               2006 issued by the FMC Trust pursuant to its Amended and Restated
               Declaration of Trust dated as of November 27, 1996, as it may be
               amended, restated or modified as permitted by Section 8.9, and
               (ii) the 1996 Subordinated Notes.

                    "1996 Subordinated Notes" means the 9% Senior Subordinated
               Notes due December 1, 2006 issued to evidence the loans made to
               Holdings of the proceeds from the issuance by the FMC Trust of
               its 9% Trust Preferred Securities Due 2006 and the common
               securities of the FMC Trust issued to Holdings, pursuant to the
               Senior Subordinated Indenture, dated as of November 27, 1996
               among Holdings, the Subsidiary Guarantors therein defined, and
               State Street Bank and Trust Company, as successor trustee to
               Fleet National Bank, as it may be amended, supplemented or
               otherwise modified to permit the assumption of the obligations of
               the note issuer thereunder by a wholly-owned Subsidiary of
               Holdings (other than the Company and its Subsidiaries) or
               Holdings and as permitted by Section 8.9, as such Notes may be
               assumed by any Subsidiary of Holdings.

          (b)  The definition of "Consolidated Fixed Charges" is hereby amended
          by inserting the following at the end thereof:

                    "; it being understood and agreed that any payment in
               respect of any Permitted Genu(beta)schein Transaction during such
               period shall not be a Consolidated Fixed Charge notwithstanding
               classification or 


                                       2

<PAGE>   3


               reclassification of the investment securitization issued in
               connection with such Permitted Genu(beta)schein Transaction as
               indebtedness under GAAP."

          (c)  The second proviso to the definition of "Material Subsidiary" is
          hereby amended as follows:

                    (i) by deleting the words "the subordinated notes given by
               Holdings to the FMC Trust in connection with the Refinancing
               Securities" in clause (i) thereof and inserting a reference to
               the "1996 Subordinated Notes" in place thereof; and

                    (ii) by deleting clause (ii) thereof and substituting the
               following therefor:

                    "(ii) for purposes of determining whether any special
               purpose wholly-owned Subsidiary of Holdings that issues or
               assumes Refinancing Securities, Additional Subdebt and/or
               Additional Subdebt Securities is a Material Subsidiary hereunder,
               the proceeds of such Refinancing Securities and/or Additional
               Subdebt Securities shall not be considered as assets for purposes
               hereof, to the extent that such proceeds have been lent or
               contributed to another member of the Consolidated Group, and any
               interest in respect of any such loan shall not be considered for
               the purposes of determining Consolidated EBITDA under this
               definition."

          (d)  The definition of "Permitted Investments" is hereby amended as
          follows:

                    (i) by deleting the words "the loan by the FMC Trust to
               Holdings of the proceeds of the Refinancing Securities (as
               described in the description of Refinancing Securities in
               Schedule 1.1)" from clause (xvi) thereof and inserting a
               reference to "the 1996 Subordinated Notes" in their place; and

                    (ii) by deleting clause (xvii) thereof and substituting
               therefor the following:

                    "(xvii) Investments by Holdings and its Subsidiaries (other
               than the Company or its Subsidiaries) in FMC Finance or any
               wholly-owned Subsidiary of Holdings that issues or assumes
               Refinancing Securities, Additional Subdebt and/or Additional
               Subdebt Securities;"

          (e)  Section 8.10(b) is hereby amended by inserting the following
          sentence at the end thereof:

                    "In addition, Holdings shall not make or permit its
               Subsidiaries to make payments in connection with any put or call
               option relating to investment securities issued under any
               Permitted Genu(beta)schein Transaction; provided that Holdings
               and its Subsidiaries (other than FUSA, the Company and their
               Subsidiaries) may make such payments in 


                                       3

<PAGE>   4

               an aggregate amount of up to $75 million so long as no Default or
               Event of Default shall exist before or after giving effect
               thereto."

          3.   The Paying Agent, with the consent and at the discretion of the
     Required Lenders, hereby consents to the Amendment by and between Holdings
     and State Street Bank and Trust Company, as successor trustee and
     collateral agent to Fleet National Bank, to the Pledge and Security
     Agreement dated as of November 27, 1996 by and between Holdings and Fleet
     National Bank, in substantially the form annexed hereto as Exhibit B, or
     such other form not less favorable in any material respect to the Lenders.

          4.   Section 7.9(a) is hereby amended by adding the words "minus (v) 
     any loss (calculated as the difference between the book value of the
     disposed assets and the net purchase price of such assets) resulting from
     the disposal of the Company's homecare and diagnostic businesses" at the
     end of the first sentence thereof.

          5.   Section 8.1(f) is hereby amended by (i) adding the words 
     "Holdings and" before the words "Foreign Subsidiaries" in the first line
     thereof and (ii) adding the words "and no more than $50,000,000 of such
     Funded Debt may be incurred, created or assumed by Holdings (except as a
     Guaranty Obligation)" at the end of clause (iii) of the proviso.

          6.   In clause (A) of the proviso to Section 8.4(c)(vi) the reference
     to "two and one half percent (2 1/2%)" is amended and increased to read
     "five percent (5%)".

          7.   In connection with the sale of the Company's homecare and
     diagnostic businesses:

          (i)  NMC Homecare, Inc. is hereby released from its obligations under
     the guaranty.

          (ii) losses from or on account of operations, discontinuation of
     operations and/or disposal of assets on account of the sale of the
     Company's homecare and diagnostic business, net of related tax effects, to
     the extent not considered extraordinary items, shall be excluded from
     Consolidated Net Income for purposes of determining the Consolidated
     Leverage Ratio and the Consolidated Fixed Charge Coverage Ratio.

          8.   The Lenders hereby waive compliance with the provisions of the
     Credit Agreement as in effect before the execution and delivery of this
     Amendment No. 6 to the extent, and only to the extent, that any transaction
     or action of any member of the Consolidated Group would have been permitted
     by the provisions of the Credit Agreement as amended hereby.

     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.


                                       4
<PAGE>   5


     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]



                                       5
<PAGE>   6


     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 J. Lipps
                                     --------------------------------------
                                  Name: Ben J. Lipps
                                  Title: President


                                  FRESENIUS MEDICAL CARE AG


                                  By: /s/ Udo Werle
                                     --------------------------------------
                                  Name:  Udo Werle
                                  Title: CEO


                                  By /s/ Dr. D. Blumenhagen
                                     --------------------------------------
                                  Name: Dr. D. Blumenhagen
                                  Title: Treasurer


                                  NMC DO BRASIL LTDA.,
                                  a Brazil corporation


                                  By /s/ Joao Padrinsui
                                     --------------------------------------
                                  Name: Joao Padrinsui
                                  Title:   Manager


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

                                  By /s/ Manuel Huete Mendez
                                     --------------------------------------
                                  Name: Manuel Huete Mendez
                                  Title: Board Member


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


                                  By /s/ William F. Grieco
                                     --------------------------------------
                                  Name: William F. Grieco
                                  Title: Assistant Secretary



                                       6
<PAGE>   7


                                  NMC CENTRO MEDICO NACIONAL, LDA.,
                                  a Portuguese corporation

                                  By /s/ Michael John Allen
                                     --------------------------------------
                                  Name: Michael John Allen
                                  Title: Board Member


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


                                  By /s/ M. Guasco
                                     --------------------------------------
                                  Name:  M. Guasco
                                  Title: President


                                  FRESENIUS USA, INC.,
                                  a Massachusetts corporation


                                  By /s/ Heinz J. Schmidt
                                     --------------------------------------
                                  Name: Heinz J. Schmidt
                                  Title: Vice President


                                  FRESENIUS MEDICAL CARE DEUTSCHLAND GmbH,
                                  a German corporation


                                  By /s/ Udo Werle   /s/ Dr. D. Blumenhagen
                                     --------------------------------------
                                  Name: Udo Werle    Dr. D. Blumenhagen
                                  Title: CEO         Treasurer


                                  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/ Dr. E. Gatti
                                     --------------------------------------
                                  Name: Dr. E. Gatti
                                  Title: Board Member




                                       7
<PAGE>   8


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

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


                                 FRESENIUS MEDICAL CARE MAGYAROSZA KfG,
                                 a Hungarian corporation


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


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


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


                                 NATIONAL MEDICAL CARE, INC.,
                                 a Delaware corporation


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


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


                                 By /s/ Heinz J. Schmidt
                                    --------------------------------------
                                 Name: Heinz J. Schmidt
                                 Title: Treasurer


                                 NMC HOMECARE, INC.,
                                 a Delaware corporation


                                 By /s/ Heinz J. Schmidt
                                    --------------------------------------
                                 Name: Heinz J. Schmidt
                                 Title: Treasurer



                                       8
<PAGE>   9

                                  LIFECHEM, INC.,
                                  a Delaware corporation

                                  By /s/ Heinz J. Schmidt
                                     --------------------------------------
                                  Name: Heinz J. Schmidt
                                  Title: Treasurer


                                  FRESENIUS MEDICAL CARE AG,
                                  a German corporation


                                  By /s/ Udo Werle   /s/ Dr. D. Blumenhagen
                                     --------------------------------------
                                  Name: Udo Werle    Dr. D. Blumenhagen
                                  Title: CEO         Treasurer


                                  FRESENIUS USA, INC.,
                                  a Massachusetts corporation


                                  By /s/ Heinz J. Schmidt
                                     --------------------------------------
                                  Name: Heinz J. Schmidt
                                  Title: Vice President


                                  FRESENIUS MEDICAL CARE DEUTSCHLAND
                                  GmbH, a German corporation


                                  By /s/ Udo Werle   /s/ Dr. D. Blumenhagen
                                     --------------------------------------
                                  Name: Udo Werle    Dr. D. Blumenhagen
                                  Title: CEO         Treasurer


                                  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


                                  FRESENIUS SECURITIES, INC.,
                                  a California corporation


                                  By /s/ Heinz J. Schmidt
                                     --------------------------------------
                                  Name: Heinz J. Schmidt
                                  Title: Vice President



                                       9
<PAGE>   10


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





                                       10
<PAGE>   11

                                    EXHIBIT A

       Description of Transactions Relating to the 1996 Subordinated Notes

SUPPLEMENTAL INDENTURES

     Set forth below is a description of the Amendments to the Indenture to be
contained in one or more supplemental indentures which, if effected, would
substitute LuxCo, a limited liability company (Societe a responsabilite limitee)
organized under the laws of Luxembourg (the "Note Issuer"), as obligor under the
Indenture for Fresenius Medical Care. Fresenius Medical Care will
unconditionally guarantee the obligations of LuxCo so that the Holders will have
the same creditors' rights as currently exist with respect to the Company. The
discussion below is qualified in its entirety by reference to the Indenture and
the supplemental indentures.

     All references to the Company relating solely to it in its capacity as (i)
primary obligor of the Securities or (ii) issuer of the Securities, shall become
references to the Note Issuer, which term will be defined. References to the
Company in the covenants that do not specifically relate to it in its capacity
as primary obligor of the Securities and other references relating to its role
as Sponsor under the Declaration will remain references to the Company. Certain
references to the Company will become references to both the Company and the
Note Issuer where applicable.

     The definitions of "Intercreditor Agreement" and "Pledge Agreement" will be
amended to clarify that they refer to such agreements as amended or supplemented
from time to time.

     The term "Subsidiary Guarantors" will be replaced by "Guarantors" which
will be defined to mean the Subsidiary Guarantors and the Company, and an
unconditional guarantee of the Note Issuer's obligations, subordinated to the
same extent as the Company's present obligations with respect to the Securities,
by Fresenius Medical Care will be added.

     The term "Successor" will be added to refer to a successor to the Note
Issuer.

     The term "Guaranty" will replace the term "Subsidiary Guaranty" and be
defined to mean the Guarantee by a Guarantor of the Note Issuer's obligations
with respect to the Securities.

     The definition of "Company" will be revised to mean Fresenius Medical Care
AG, a stock corporation (Aktiengesellschaft) organized under the laws of the
Federal Republic of Germany, and its permitted successors and assigns.

     The terms "Guarantor Blockage Notice," "Guarantor Payment Blockage Period"
and "Guarantor Senior Subordinated Payment" will replace the terms "Subsidiary
Guarantor Blockage Notice," "Subsidiary Guarantor Payment Blockage Period" and
"Subsidiary Guarantor Senior Subordinated Payment."

     The definition of "Tax Event" will be conformed to that in the amendment to
the Declaration contemplated hereby.


<PAGE>   12

     Section 3.3 will be amended to enable any duly authorized officer or
officers of the Note Issuer to execute the Securities.

     Sections 3.12, 4.1(3), 4.3(3), 10.19(a) and 11.7(b), relating to certain
tax matters, and Sections 5.1(6) and (7), relating to bankruptcy events of
default, will be amended to cover circumstances that could arise from the Note
Issuer being formed under a different jurisdiction than that of the Company.

     Section 8.1(4) and Section 8.1(6), concerning exceptions to the prohibition
against merger or consolidation, will be deleted. Accordingly, Section 8.1(5)
will become Section 8.1(4) and Section 8.1(7) will become Section 8.1(5). A
provision similar to Section 8.1(4) will be added to Section 8.2 concerning
mergers or consolidations of the Guarantors as a condition to any merger or
consolidation of the Company. A new Section 8.1(6) will be added to permit
merger or consolidation when such merger or consolidation is permitted under the
Declaration and does not give rise to any breach or violation of the
Declaration.

     Section 8.3 will be amended to add a first paragraph providing that the
Company or a wholly-owned Subsidiary (a "Successor") may assume the obligations
of the Note Issuer under the Securities by executing and delivering to the
Trustee (a) a supplemental indenture which subjects such Person to the
provisions (including the representations and warranties) of the Indenture as a
Note Issuer and (b) an Opinion of Counsel (as defined in the Indenture) to the
effect that such supplemental indenture has been duly authorized and executed by
such Person and constitutes the legal, valid, binding and enforceable obligation
of such Person, subject to customary exceptions; provided, that the assumption
of such obligations by the Successor shall not cause the Trust to fail or cease
to be classified for U.S. federal income tax purposes as a grantor trust or
another entity which is not subject to U.S. federal income tax at the entity
level and the assets and income of which are treated for U.S, federal income tax
purposes as held and derived directly by holders of interests in the Trust and,
provided, further, that the Company will continue to unconditionally guarantee,
on a senior subordinated basis, the obligations of such Successor. The Successor
will succeed to, and be substituted for, and may exercise every right and power
of, the Note Issuer under the Indenture with the same effect as if the Note
Issuer therein, and the former Note Issuer will be discharged from all
obligations and covenants under the Indenture and the Securities. The references
to "Surviving Person" in the old second paragraph (new third paragraph) of
Section 8.3 will be amended to refer to "Surviving Person or Successor."

     The Subsidiary Guaranty provisions set forth in Article XIII will be
revised to effect the following Amendments, (i) the term "Guarantors" will
replace the term "Subsidiary Guarantors" wherever it appears; (ii) the term
"Note Issuer" will replace the term "Company" wherever it appears, except in the
description of the parties to the Profit and Loss Pooling Agreement dated August
21, 1996 therein described; and (iii) references to "this Guaranty" will replace
references to "this Subsidiary Guaranty."

     Conforming changes will be made to the form of guaranty set forth in
Section 2-6 and the form of Securities set forth in Article III.


<PAGE>   13


AMENDMENTS TO THE DECLARATION

     Set forth below is a description of the Amendments to the Declaration
which, if effected, would substitute the reference to the Note Issuer for
references to Fresenius Medical Care when Fresenius Medical Care is referred to
solely in its capacity as issuer of the Securities. The discussion below is
qualified in its entirety by reference to the Declaration and the Amendment to
the Declaration.

     The definition of the term "Note Issuer" will be added.

     The definition of "Notes" will be amended to delete the reference to the
"Sponsor" contained therein.

     The definition of the term "Sponsor" will be amended to refer to the Note
Issuer rather than the Company in certain circumstances where it relates solely
to the issuer of the Securities.

     The definition of the term "Tax Event" will be amended to cover
circumstances that could arise from the Note Issuer being formed under a
different jurisdiction than that of the Company.

     Section 2.7(d) relating to operating the Trust so that it is not taxed as a
corporation and so that the Securities will be treated as indebtedness for tax
purposes, will be amended to cover circumstances that could arise from the Note
Issuer being formed under a different jurisdiction than that of the Company.

     Each of Section 6.1(b) and Section 6.1(c) relating to limitations on voting
rights will be amended by inserting, at the end of the first sentence of each
such section, a proviso to the effect that the Indenture cannot be amended in
any way which would cause the Trust to fail or cease to be classified for
purposes of United States federal income taxation as other than a grantor trust
or other entity which is not subject to United States federal income tax at the
entity level and the assets and income of which are treated for United States
federal income tax purposes as held and derived directly by holders of interests
in the entity.

     Section 9.4(e) relating to redemption of the Securities in lieu of
distribution thereof to the Holders following a Tax Event (as defined therein)
in certain tax circumstances will be amended to cover circumstances that could
arise from the Note Issuer being formed under a different jurisdiction than that
of the Company.


AMENDMENT TO THE GUARANTEE AGREEMENT

     The Amendment to the Guarantee Agreement, if effected, would clarify that
references to the Indenture are references to the Indenture as amended or
supplemented from time to time.


<PAGE>   14


AMENDMENT TO THE PLEDGE AGREEMENT

     The Amendment to the Pledge Agreement, if effected, would amend the
definition of the term "Secured Obligations" to include amounts owed by the
Company under its obligations as a guarantor, rather than the issuer, of the
Securities. The Amendment to the Pledge Agreement requires the consent of the
Senior Bank Agent (as defined in the Intercreditor Agreement).


AMENDMENTS TO THE INTERCREDITOR AGREEMENT

     The Amendment to the Intercreditor Agreement, if effected, would clarify
that references to the Pledge Agreement are references to the Pledge Agreement
as amended from time to time.



<PAGE>   15


                                    EXHIBIT B

               Form of Amendment to Pledge and Security Agreement


                                  AMENDMENT TO
                          PLEDGE AND SECURITY AGREENMNT

     THIS AMENDMENT TO PLEDGE AND SECURITY AGREEMENT ("Amendment") dated as of
_____________, 1998, by and between Fresenius Medical Care AG, as Pledgor
("Company") and State Street Bank and Trust Company, as successor trustee and
collateral agent to Fleet National Bank (in such capacity, together with its
successors in such capacity, "Collateral Trustee") under the Indenture, hereby
amends the Pledge and Security Agreement dated as of November 27, 1996 by and
between Company and Collateral Trustee (as such agreement may be amended or
supplemented from time To time, the "Pledge Agreement"). Capitalized terms used
herein and not defined shall have the meanings ascribed to such terms in the
Pledge Agreement.

                                    RECITALS

     WHEREAS, Company and Collateral Trustee desire to amend the Pledge
Agreement to clarify the Pledge Agreement in connection with amendments to the
Indenture; and

     WHEREAS, the consent of the Senior Bank Agent and a majority of the Holders
has been obtained;

     NOW, THEREFORE, for and in consideration of the promises and of the mutual
covenants herein contained and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties agree as
follows:


                                    ARTICLE I
                          AMENDMENT TO PLEDGE AGREEMENT

     SECTION 1.01.  Definition of Secured obligations. The definition of 
"Secured Obligations is hereby amended to read as follows,

           "Secured Obligations" shall mean all amounts from time to 
           time owing to the Holders of the Securities or the                 
           Collateral Trustee by the Company under its Guarantee or           
           under the Indenture."                                              
           

<PAGE>   16


                                   ARTICLE II
                                  MISCELLANEOUS

     SECTION 2.01.  Section 6.06 of the Pledge Agreement. This Amendment meets
the requirements of Section 6.06 of the Pledge Agreement concerning amendments,
including compliance with Section 9.2 of the Indenture. Upon execution and
delivery of this Amendment, the terms and conditions of this Amendment shall be
part of the terms and conditions of the Pledge Agreement for any and all
purposes, and all the terms and conditions of both shall be read together as
though they constitute one and the same instrument, except that in case of
conflict, the provisions of this Amendment will control.

     SECTION 2.02.  Full Force and Effect. Except as they have been modified in
this Amendment, each and every term and provision of the Pledge Agreement shall
continue in full force and effect, and all references to the Pledge Agreement in
the Pledge Agreement shall be deemed to mean the Pledge Agreement as
supplemented and amended pursuant hereto.

     SECTION 2.03.  Counterparts. This Amendment maybe executed in any number of
counterparts and in separate counterparts, each of which when so executed shall
be deemed to be an original, but all of which counterparts shall together
constitute but one and the same instrument.

     SECTION 2.04.  Governing Law. This Amendment shall be governed by and
construed in accordance with the laws of the State of New York without giving
effect to principles of conflicts of laws.

     SECTION 2.05.  Headings. The headings of the Articles and Sections of this
Amendment have been inserted for convenience of reference only, and are not to
be considered a part hereof and shall in no way modify or restrict any of the
terms and provisions hereof


         [The remainder of this page has been intentionally left blank]


<PAGE>   17



     IN WITNESS WHEREOF, the parties have caused this Amendment to be duly
executed as of the day and year first above written.


                                      FRESENIUS MEDICAL CARE AG


                                      By: ______________________________________
                                           Name:
                                           Title:

                                      By: ______________________________________
                                           Name:
                                           Title:


                                      STATE STREET BANK AND TRUST
                                      COMPANY, as Collateral Trustee

                                      By: ______________________________________
                                           Name:
                                           Title: