Document:

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                                                                   Exhibit 10.72

4 March 1999

Mr K Kasses
Genta Incorporated
99 Hayden Avenue
Lexington
MA 02421
USA

Dear Ken

THE GENTA - JAGO JOINT VENTURE

The parties have been discussing a means of resolving their involvement in Genta
Jago Technologies BV (the Joint Venture) and the several agreements in being
between them concerning its operation and activities.

Genta is evaluating the fiscal and other consequences of acquiring SkyePharma's
interest in the Joint Venture. Regardless of the outcome of such evaluation, the
parties hare agreed to operate the activities of the Joint Venture in accordance
with what follows notwithstanding anything contained in the several agreements
referred to above. For the avoidance of doubt, SkyePharma shall mean all members
of the SkyePharma Group of Companies, on whose behalf SkyePharma commits.
SkyePharma is referred to as "Skye" hereafter.

1.   The Parties  waive, release and hold each other harmless and each of
     their respective partners, affiliates, shareholders, directors, officers,
     agents, advisors, representatives, employees, counsel and controlling
     persons within the meaning of the Securities Act of 1933, as amended (the
     "Act"), from any and all losses, liabilities, claims, damages and expenses,
     whether known or unknown, contingent or matured (collectively, the
     "Claims") whatsoever in any way related to, arising out of or in connection
     with (i) any and all unpaid development costs accrued as of the date
     hereof, (ii) the certain notes executed by the Joint Venture in favour of
     Genta for the funding of development and operational costs, and (iii) any
     and all obligations and/or responsibilities under the agreements set forth
     in Schedule A, including, without limitation, specifically Genta shall be
     released in all respects from the funding obligations under any such
     agreements.

2.   Henceforth, and pending the outcome of Genta's evaluation (mentioned
     above) and/or such other agreement as may be made between the parties, Skye
     shall benefit from all rights and become responsible for all obligations
     under existing development and license agreements between the Joint Venture
     and independent third parties, including Apothecon (now terminated),
     Brightstone and Krypton. Skye shall be solely responsible for the further
     development, marketing, distribution, manufacturing and funding of the
     Joint Venture products listed in Schedule B of the Restated Geomatrix
     License Agreement ("JV Products"), now being Schedule B to this agreement.
     In order to enable these  provisions to work Skye is hereby given authority
     to commit the Joint Venture in

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     all particulars, with third parties and without need of any further
     assurance from Genta or the signature of any of its officers.

3.   In consideration of the foregoing, the Joint Venture shall have a vested
     interest in the qualified income share from the license revenues of Skye
     relating to JV Products (the "Qualified  Income Share"), including license
     fees, milestones, royalties and other payments made in respect of a license
     granted in respect of the JV Products ("License Income"), but excluding
     reasonable and documented reimbursements by independent third parties for
     development costs and expenses of Skye. The Qualified Income Share shall be
     as follows:

     (a)   For JV Products for which the Joint Venture  and/or Skye have
           initiated development prior to the date hereof (as set forth
           of Schedule B), that:

           (i)   have been, or are in the future, licensed to independent third
                 parties, the Qualified Income Share of the Joint Venture
                 shall be equal to one hundred  percent (100%) of the License
                 Income; and

           (ii)  have been, or are in the future, licensed to an affiliate
                 company within the Skye group, the Qualified Income Share of
                 the Joint Venture shall be based on the terms for payments
                 owed to the Joint Venture pursuant to the license agreement
                 for  Naproxen entered into on 25th October 1996 between the
                 Joint Venture and Krypton Ltd., a wholly owned subsidiary of
                 Skye.

     (b)   For JV Products for which no development has occurred prior to
           the date hereof (as set forth in  Schedule C), that are in the
           future licensed to independent third parties or affiliates of Skye:

           (i)   within eighteen (18) months, then the Qualified Income Share
                 of the Joint Venture shall be 100% of the License Income; and

           (ii)  thereafter, the Qualified Income Share of the Joint Venture
                 shall be sixty-six percent (66%) of the License Income; and

           (iii) 3.(a)(ii) above shall apply to the determination of licence
                 income for licences to affiliate companies within the Skye
                 Group.

     (c)   For JV Products for which no development has occurred prior to
           the date hereof (as set forth in Schedule C), Skye is entitled
           to deduct from License Income actually received from independent
           third parties for each such product worked on prior to the
           execution of the development/license agreement with such
           independent third party up to an aggregate amount of CHF 500,000 per
           product/license to cover unreimbursed development fees that are
           incurred for such products.

4.   Until the date that is nineteen (19) years from the date hereof, all
     Qualified License Income shall be paid by Skye immediately upon receipt
     into an escrow account in the
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     name of the JV Company,  jointly controlled (for payments out) by Genta and
     Skye or their nominees (the "Escrow Account"). Any amounts received in the
     Escrow Account shall be disbursed to the Parties and Vecap Venture Capital
     Partners AG ("Vecap") pursuant to the Distribution List attached hereto as
     Schedule  D. Upon full  recovery of all amounts set forth for the credit of
     each of the Parties and Vecap, Genta and Skye shall each receive fifty
     percent (50%) of all additional Qualified License Income.

5.   Subject to the further agreement between the parties the Joint Venture
     shall be maintained by an independent third party (appointed by agreement),
     on behalf of the parties, on a minimal basis, with only those functions
     performed by it or in relation to it, which are strictly  necessary  for
     purposes of this agreement, and/or to maintain the integrity of its
     Corporate being (audit and registration fees, etc). For avoidance of doubt
     such independent third party will invoice both Genta and Skye for 50% each
     of any necessary costs and expenses, reasonably incurred in the fulfillment
     of this paragraph 5.

Both parties acknowledge that this agreement represents an interim solution and
that it shall obtain until they are able to resolve the relationship between
them to their mutual satisfaction.

If the foregoing accurately reflects your understanding of what we have agreed,
will you please evidence accordingly by signing and returning one copy of this
agreement.

Yours sincerely

PETER WARBURTON
COMPANY SECRETARY & INTERNATIONAL COUNSEL

FOR:  GENTA INCORPORATED

BY: _________________________________       DATE: ____________________________
NAME:
TITLE:<PAGE>   1
                                                                    Exhibit 4.10

                                 AMENDMENT NO. 8

      THIS AMENDMENT NO. 8, dated as of June 30, 1999 (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 modification of certain covenants and
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:

      1. Section 8.1 of the Credit Agreement is hereby amended by deleting the
word "and" from the end of clause (i) thereof, deleting the period from the end
of clause (vi) thereof and inserting "; and" in its place and inserting the
following immediately thereafter as a new clause (n):

            "(n) in addition to other indebtedness permitted by this Section
      8.1, Indebtedness of Holdings and its Subsidiaries owed to Fresenius AG or
      any of its Subsidiaries in an aggregate principal amount not to exceed
      $400 million at any time outstanding; provided, that such Indebtedness
      shall be subordinated to the Obligations on terms no less favorable to the
      Lenders than the terms of the subordinated debt related to and included
      within the definition of Refinancing Securities, the Additional Subdebt,
      and the related guaranties; it being understood and agreed that any
      Indebtedness that has been subordinated to the payment of the Obligations
      pursuant to the provisions hereof shall not be considered a
<PAGE>   2
      Subordinated Debt Transaction for purposes of Section 3.3 or Subordinated
      Debt for purposes of Section 8.9."

      2. The Lenders hereby waive compliance with the provisions of the Credit
Agreement as in effect before the execution and delivery of this Amendment No. 8
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.

      3. This Amendment shall be effective upon receipt by the Paying Agent of
(i) copies of this Amendment executed by the Company and the other members of
the Consolidated Group identified on the signature pages hereto, and (ii) the
consent of the Required Lenders to this Amendment.

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

      5. 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.

      6. 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.

      7. 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.

                                       2
<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/ Dr. Emanuele Gotti
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti
                              Title: Member of the Board of Management

                              By /s/ Dr. Werner Brandt
                                 -----------------------------------------------
                              Name:  Dr. Werner Brandt
                              Title: Member of the Board of Management

                              NMC DO BRASIL LTDA.,
                              a Brazil corporation

                              By /s/ Joao Pedrinelli
                                 -----------------------------------------------
                              Name:  Joao Pedrinelli
                              Title: Member of the Board of Directors

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

                              By /s/ Dr. Emanuele Gotti   /s/ Dr. Andrea Stopper
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti,      Dr. Andrea Stopper
                              Title: Board Member             Board Member

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

                              By /s/ Roberto Fuste        /s/ Betty Na
                                 -----------------------------------------------
                              Name:  Roberto Fuste            Betty Na
                              Title: Members of the Board of Directors
<PAGE>   4
                              NMC CENTRO MEDICO NACIONAL, LDA.,
                              a Portuguese corporation

                              By /s/ Ricardo Da Silva     /s/ John Allen
                                 -----------------------------------------------
                              Name:  Ricardo Da Silva,        John Allen
                              Title: Board Members

                              FRESENIUS MEDICAL CARE ARGENTINA, S.A.,
                              as successor by merger to
                              NMC DE ARGENTINA, S.A.,
                              an Argentine corporation

                              By /s/ Dr. Guido Yagupsky   /s/ Horst Radthe
                                 -----------------------------------------------
                              Name:  Dr. Guido Yagupsky,      Horst Radthe
                              Title: Board Members

                              FRESENIUS USA, INC.,
                              a Massachusetts corporation

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

                              FRESENIUS MEDICAL CARE DEUTSCHLAND GmbH,
                              a German corporation

                              By /s/ Dr. Emanuele Gotti
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti
                              Title: Board Member

                              By /s/ Dr. Werner Brandt
                                 -----------------------------------------------
                              Name:  Dr. Werner Brandt
                              Title: Board Member

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

                              By /s/ Udo Werle            /s/ Heinz Henrici
                                 -----------------------------------------------
                              Name:  Udo Werle                Heinz Henrici
                              Title: Board Members
<PAGE>   5
                              FRESENIUS MEDICAL CARE HOLDING, S.p.A.,
                              an Italian corporation

                              By /s/ Dr. Emanuele Gotti   /s/ Dr. Andrea Stopper
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti       Dr. Andrea Stopper
                              Title: Board Members

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

                              By /s/ Dr. Emanuele Gotti   /s/ Manuel Gluete
                                 -----------------------------------------------
                              Name:  Dr. Emanuel Gotti        Manuel Gluete
                              Title: Board Members

                              FRESENIUS MEDICAL CARE MAGYAROSZA KfG,
                              a Hungarian corporation

                              By /s/ Norman Erhard
                                 -----------------------------------------------
                              Name:  Norman Erhard
                              Title: Board Member

GUARANTORS:                   FRESENIUS 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/ Marc Lieberman
                                 -----------------------------------------------
                              Name:  Marc Lieberman
                              Title: Assistant Treasurer
<PAGE>   6
                              LIFECHEM, INC.,
                              a Delaware corporation

                              By /s/ Marc Lieberman
                                 -----------------------------------------------
                              Name:  Marc Lieberman
                              Title: Assistant Treasurer

                              FRESENIUS MEDICAL CARE AG,
                              a German corporation

                              By /s/ Dr. Emanuele Gotti
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti
                              Title: Member of the Management Board

                              By /s/ Dr. Werner Brandt
                                 -----------------------------------------------
                              Name:  Dr. Werner Brandt
                              Title: Member of the Management Board

                              FRESENIUS USA, INC.,
                              a Massachusetts corporation

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

                              FRESENIUS MEDICAL CARE DEUTSCHLAND
                              GmbH, a German corporation

                              By /s/ Dr. Emanuele Gotti
                                 -----------------------------------------------
                              Name:  Dr. Emanuele Gotti
                              Title: Board Member

                              By /s/ Dr. Werner Brandt
                                 -----------------------------------------------
                              Name:  Dr. Werner Brandt
                              Title: Board Member

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

                              By /s/ Udo Werle            /s/ Heinz Henrici
                                 -----------------------------------------------
                              Name:  Udo Werle                Heinz Henrici
                              Title: Board of Directors
<PAGE>   7
                              FRESENIUS SECURITIES, INC.,
                              a California corporation

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

                              NEOMEDICA, INC.,
                              a Delaware corporation

                              By /s/ Gary Scher
                                 -----------------------------------------------
                              Name:  Gary Scher
                              Title: Vice-President

                              FMC FINANCE S.A.,
                              a Luxembourg corporation

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

                              FMC TRUST FINANCE S.a.r.l. LUXEMBOURG,
                              a Luxembourg corporation

                              By /s/ Dr. Andrea Stopper
                                 -----------------------------------------------
                              Name:  Dr. Andrea Stopper
                              Title: Board Member

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

                              By /s/ Ashley M. Crabtree
                                 -----------------------------------------------
                              Name:  Ashley M. Crabtree
                              Title: Senior Vice President
<PAGE>   8
                           CONSENT TO AMENDMENT NO. 8

NationsBank, N.A., as Paying Agent
101 N. Tryon Street, 15th Floor
NC1-001-15-04
Charlotte, North Carolina 28255
Attn:  Cindy Harmon, 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. 8 dated June 30, 1999 (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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