<PAGE>

                                                                   EXHIBIT 10.20

                                       1

================================================================================

                                   Amendment
                                       to
                              Amended and Restated
                              Investment Agreement

                                     among

                               MSF HOLDING LTD.,

                         MEDICAL SYSTEMS FINANCE S.A.,

                                  ESTOLUR S.A,

                        HEALTHCARE SYSTEMS FINANCE S.A.,

                            MSF/HSF ARGENTINA S.A.,

                                      and

      NEDERLANDSE FINANCIERINGS-MAATSCHAPPIJ VOOR ONTWIKKELINGSLANDEN N.V.



                              Dated July 19, 2001

================================================================================
<PAGE>

                                  AMENDMENT TO
                              AMENDED AND RESTATED
                              INVESTMENT AGREEMENT


     AGREEMENT, dated July 19, 2001, among MSF HOLDING LTD., a company organized
and existing under the laws of the Commonwealth of the Bahamas ("MSF Holding"),
MEDICAL SYSTEMS FINANCE S.A. ("MSF"), ESTOLUR S.A. ("Estolur"), HEALTHCARE
SYSTEMS FINANCE S.A. ("HSF"), each of them a sociedad anonima, organized and
                                             -------- -------
existing under the laws of Uruguay, and MSF/HSF ARGENTINA S.A., a sociedad
                                                                  --------
anonima organized and existing under the laws of Argentina, formerly known as
-------
Sistemas Financieros S.A. and as MSF Argentina S.A. ("MSF Argentina"), and
NEDERLANDSE FINANCIERINGS-MAATSCHAPPIJ VOOR ONTWIKKELINGSLANDEN N.V., a limited
liability company organized and existing under the laws of The Netherlands
("FMO").

     WHEREAS:

     (A) Pursuant to an Amended and Restated Investment Agreement dated April
27, 1998, as amended and restated as of September 29, 1998 and as further
amended (as amended from time to time, the "Investment Agreement") among the
parties hereto, FMO has made a loan to the Co-Borrowers (as such term and other
terms used herein are defined in Section 1) in the aggregate principal amount of
up to twenty-five million Dollars ($25,000,000).

     (B) FMO and the Co-Borrowers have agreed to amend the Investment Agreement
as provided herein.

     NOW, THEREFORE, the parties agree as follows:

     Section 1.  Definitions.  All capitalized terms used in this Agreement
(including the preamble and recitals) and not otherwise defined herein, unless
the context otherwise requires, have the respective meanings given to such terms
in the Investment Agreement.

     Section 2.  Amendments to the Investment Agreement.

     (a) Section 1.01 of the Investment Agreement is amended by inserting in
such section in alphabetical order the following additional definitions:
<PAGE>

                                       2

          "Contract Repurchase Guarantee Agreement" an agreement among DVI
Financial, Oferil and the Co-Borrowers, in form and substance acceptable to FMO,
(i) obligating Oferil to purchase Defaulted Receivables in an amount in each
fiscal Year at least equal to the difference between two percent (2%) of Net
Financed Assets and the amount of the Lease/Loan Loss Reserve at a price equal
to the amount of such Defaulted Receivables and (ii) providing for the payment
for each Defaulted Receivable purchased by the reduction of the principal amount
of the loans outstanding under the Stand-by Loan Facility Agreement by the
amount of such Defaulted Receivable;

          "Defaulted Receivable" any Lease/Loan Receivable in respect of which
any amount is due and unpaid for one hundred eighty-one (181) days or more;

     (b)  Section 1.02 of the Investment Agreement is amended by inserting in
such section in alphabetical order the following additional definition:

          "Debt to Equity Ratio" the result obtained by dividing Debt by
Shareholders' Equity;

     (c)  Section 3.07(a)(i) of the Investment Agreement is amended to reach as
follows:

          (i) the Co-Borrowers simultaneously pay all accrued interest and
     Maintenance Amount (if any) on the amount of the Loan to be prepaid
     together with (A) a prepayment premium in an amount equal to one and one-
     half percent (1.5%) of the amount of the Loan being prepaid and (B) all
     other amounts then due and payable under this Agreement.

     (d)  Section 7.02(b) of the Investment Agreement is amended to read as
follows:

          (b) cause the Eligible Co-Borrowers to maintain on a consolidated
     basis a diversified vendor portfolio, with no single vendor
<PAGE>

                                       3

     providing more than (i) 50% of the equipment financed pursuant to Eligible
     Leases/Loans in the MSF Portfolio from July 1, 2002 through June 30, 2003,
     and (ii) 40% of such equipment thereafter;

     (e)  Section 7.03(b) of the Investment Agreement is amended to read as
follows:

          (b) maintain, on an aggregate basis, a diversified vendor lease
     portfolio, with no single vendor representing more than (i) fifty percent
     (50%) of the equipment financed pursuant to Eligible Leases/Loans in the
     MSF Portfolio from July 1, 2002 through June 30, 2003, and (ii) forty
     percent (40%) of such equipment thereafter;

     (f)  Section 7.02(c) of the Investment Agreement is amended to read as
follows:

          (c) maintain a Lease/Loan Loss Reserve of at least (i) one percent
     (1%) of Net Financed Assets during Fiscal Year 1999, (ii) one and one-half
     percent (1.5%) of Net Financed Assets during Fiscal Year 2000, and (iii)
     two percent (2%) of Net Financed Assets in Fiscal Year 2001 and thereafter;
     provided, that in Fiscal Year 2001 and thereafter, MSF Holding may maintain
     a Lease/Loan Loss Reserve of at least one-half percent (0.5%) of Net
     Financed Assets if (A) the Contract Repurchase Guarantee Agreement is in
     full force and effect, (B) in each such Fiscal Year, Oferil has purchased
     from the Eligible Co-Borrowers pursuant to the Contract Repurchase
     Guarantee Agreement an amount of Defaulted Receivables at least equal to
     the difference between two percent (2%) of Net Financed Assets and the
     amount of the Lease/Loan Loss Reserve, each Defaulted Receivable so
     purchased has been paid for by the reduction of the principal amount of the
     loans outstanding under the Stand-by Loan Facility Agreement by the amount
     of such Defaulted Receivable, and DVI Financial has delivered to the Co-
     Borrowers evidence of the satisfaction of the loans so canceled, (C) the
     amount of loans outstanding under the Stand-by Loan Facility Agreement
     after giving effect to any repurchase of and payment for Defaulted
     Receivables is at least equal to the difference between two percent (2%) of
     Net Financed Assets and the amount of the Lease/Loan Loss Reserve, and (D)
     and all loans outstanding under the Stand-by Loan Facility Agreement are
     subordinated on terms acceptable to FMO to all amounts payable under this
     Agreement;

     (g)  Section 7.03(c) of the Investment Agreement is amended to read as
follows:

<PAGE>

                                       4

          (c) maintain, on an aggregate basis, a Lease/Loan Loss Reserve of at
     least (i) one percent (1%) of Net Financed Assets during Fiscal Year 1999,
     (ii) one and one half percent (1.5%) of Net Financed Assets during Fiscal
     Year 2000, and (iii) two percent (2.0%) of Net Financed Assets in Fiscal
     Year 2001 and thereafter; provided, that in Fiscal Year 2001 and
     thereafter, the Eligible Co-Borrowers may maintain on an aggregate basis a
     Lease/Loan/Loss Reserve of at least one-half percent (0.5%) of Net Financed
     Assets if (A) the Contract Repurchase Guarantee Agreement is in full force
     and effect, (B) in each Fiscal Year, Oferil has repurchased from the
     Eligible Co-Borrowers pursuant to the Contract Repurchase Guarantee
     Agreement an amount of Defaulted Receivables at least equal to the
     difference between two percent (2%) of Net Financed Assets and the amount
     of the Lease/Loan Loss Reserve, each Defaulted Receivable so purchased has
     been paid for by the reduction of the principal amount of the loans
     outstanding under the Stand-by Loan Facility Agreement by the amount of
     such Defaulted Receivable, and DVI Financial has delivered to the Co-
     Borrowers evidence of the satisfaction of the loans so canceled, (C) the
     amount of loans outstanding under the Stand-by Loan Facility Agreement
     after giving effect to any repurchase of and payment for Defaulted
     Receivables is at least equal to the difference between two percent (2%) of
     Net Financed Assets and the amount of the Lease/Loan Loss Reserve, and (D)
     all loans outstanding under the Stand-by Loan Facility Agreement are
     subordinated on terms acceptable to FMO to all amounts payable under this
     Agreement; and

     (h)  Section 7.04(a) of the Investment Agreement is amended to read as
follows:

          Section 7.04.  Negative Covenants.  Unless FMO otherwise agrees, each
     of the Co-Borrowers shall not:

     (a)  incur, assume or permit to exist any indebtedness except:

          (i)    the Loan;

          (ii)   the IFC Loan;

          (iii)  that part of Short-term Debt which is Indebtedness for Money
                 Borrowed incurred from commercial and/or investment banks in
                 the ordinary course of business, not exceeding at any one time
                 outstanding the equivalent of
<PAGE>

                                       5

                 twenty percent (20%) of the sum of (A) the aggregate principal
                 amount of Eligible Leases/Loans in the MSF Portfolio plus (B)
                 the value of the Cash Collateral pledged to FMO and IFC under
                 the Trustee Account and Security Agreement and in which FMO and
                 IFC have perfected and registered first priority security
                 interests;

          (iv)   other loans contemplated in the Financial Plan; and

          (v)    additional Debt which would not result in the Debt to Equity
                 Ratio exceeding 8:1; provided, that, at the time of incurring
                 such Debt, and after giving effect to the incurrence of such
                 Debt, no Event of Default or Potential Event of Default has
                 occurred and is continuing and that such additional Debt is not
                 secured by any assets comprising the FMO/IFC Security;

     Section 3.  Miscellaneous.

     (a)  Each of the Co-Borrowers agrees to deliver to FMO such opinions of
counsel as it may reasonably request with respect to this Agreement.

     (b)  All references in the Investment Agreement to "this Agreement",
"herein", "hereof", "hereunder", "hereto" or expressions of like meaning shall
be references to the Investment Agreement, as amended by this Agreement.

     (c)  Except as amended hereby, the Investment Agreement shall remain in
full force and effect.

     (d)  Each of the Co-Borrowers hereby restates, as if set forth herein at
length, and confirms, as of the date hereof, the representations and warranties
made by it in Article V of the Investment Agreement.

     (e)  The Co-Borrowers shall pay to FMO or as FMO may direct the reasonable
fees and expenses of  FMO's counsel in New York, the Bahamas, Uruguay,
Argentina, Mexico and elsewhere incurred in connection with (i) the preparation
and/or review, execution and, where appropriate, translation and registration of
this Agreement, and any other documents related to this Agreement; and (ii) the
giving of any legal opinions required by FMO in connection herewith.
<PAGE>

                                       6

     (f) This Agreement is governed by, and shall be construed in accordance
with, the laws of the State of New York, United States of America.

     (g) This Agreement may be executed in several counterparts, each of which
shall be considered an original, but all of which together shall constitute one
and the same agreement.

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

                              MSF HOLDING LTD.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative



                              MEDICAL SYSTEMS FINANCE S.A.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative



                              ESTOLUR S.A.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative

<PAGE>

                                       7

                              HEALTHCARE SYSTEMS FINANCE S.A.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative



                              MSF/HSF ARGENTINA S.A.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative


                              NEDERLANDSE FINANCIERINGS-MAATSCHAPPIJ
                              VOOR ONTWIKKELINGSLANDEN N.V.



                              By: _____________________________________
                                  Name:
                                  Authorized Representative


                              By: _____________________________________
                                  Name:
                                  Authorized Representative