<PAGE>

                                                                    Exhibit 10.2

                              FOURTH AMENDMENT TO
                        RECEIVABLES PURCHASE AGREEMENT
                        ------------------------------

     This Fourth Amendment to Receivables Purchase Agreement, dated as of
February 2, 2001 (this "Amendment"), is among D&K RECEIVABLES CORPORATION, a
Delaware corporation ("Seller"), D&K HEALTHCARE RESOURCES, INC., a Delaware
corporation ("Parent"), BLUE KEEL FUNDING, LLC, a Delaware limited liability
company ("Purchaser"), and FLEET NATIONAL BANK, a national banking association,
as administrator for Purchaser (in such capacity, the "Administrator").

                                  BACKGROUND

     1.   Seller, Parent, Purchaser and the Administrator are parties to that
certain Receivables Purchase Agreement, dated as of August 7, 1998, as amended
by the First Amendment to Receivables Purchase Agreement, dated as of December
17, 1998, by the Second Amendment to Receivables Purchase Agreement, dated as of
June 1, 1999, and by the Third Amendment to Receivables Purchase Agreement,
dated as of March 31, 2000 (the "Receivables Purchase Agreement").

     2.   The parties hereto desire to amend the Receivables Purchase Agreement
in certain respects as set forth herein.

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto hereby agree as follows:

     SECTION 1.  Definitions. Capitalized terms used in this Amendment and not
otherwise defined herein shall have the meanings assigned thereto in the
Receivables Purchase Agreement.

     SECTION 2.  Purchase Limit. Section 1.01 of the Receivables Purchase
Agreement is hereby amended by deleting the number "$75,000,000" where it
appears in clause (a) thereof and substituting therefor the phrase "$100,000,000
for the period from February 2, 2001 until April 1, 2001 and $75,000,000 from
and after April 1, 2001".

     SECTION 3.  Dynamic Loss Reserve Percentage. The definition of "Dynamic
Loss Reserve Percentage" that appears in Appendix A to the Receivables Purchase
Agreement is hereby amended by deleting the word "three" where it appears in the
description of the Loss Horizon therein and substituting therefor the word
"two".

     SECTION 4.  Loss Reserve. The definition of "Loss Reserve" that appears in
Appendix A to the Receivables Purchase Agreement is hereby amended by deleting
the number "8%" where it appears in clause (A)(1) thereof and substituting
therefor the number "10%".
<PAGE>

     SECTION 5.  Representations and Warranties. Each of Parent and Seller
hereby represents and warrants that, after giving effect to this Amendment, (i)
the representations and warranties contained in Article VI of the Receivables
Purchase Agreement are true and correct on and as of the date hereof and shall
be deemed to have been made on such date (except that any such representation or
warranty that is expressly stated as being made only as of a specified earlier
date shall be true and correct in all material respects as of such earlier date)
and (ii) no Liquidation Event or Unmatured Liquidation Event has occurred and is
continuing.

     SECTION 6.  Effectiveness. This Amendment shall become effective upon the
receipt by the Administrator of (i) copies of this Amendment duly executed by
Seller and Parent, (ii) the fee required to be paid in connection herewith as
set forth in the fee letter dated as of the date hereof with the Administrator
and (iii) a certificate of the Secretary or Assistant Secretary of each of
Seller and Parent certifying (A) that the certificate of incorporation and by-
laws of such Person previously delivered to the Administrator have not been
amended, except as set forth in such certificate, or revoked, (B) that attached
thereto are resolutions of its Board of Directors approving this Amendment and
(C) the names and true signatures of the officers authorized on its behalf to
execute and deliver this Amendment.

     SECTION 7.  Miscellaneous. The Receivables Purchase Agreement, as amended
hereby, remains in full force and effect. Any reference to the Receivables
Purchase Agreement from and after the date hereof shall be deemed to refer to
the Receivables Purchase Agreement as amended hereby. This Amendment may be
executed in counterparts, each of which when so executed shall be deemed to be
an original and all of which when taken together shall constitute one and the
same agreement. This Amendment shall be governed by, and construed in accordance
with, the laws of the State of New York. Seller, on demand, shall pay, or
reimburse the Administrator for, all of the costs and expenses, including legal
fees and disbursements, incurred by the Administrator or Purchaser in connection
with this Amendment.


                 [REMAINDER OF PAGE LEFT INTENTIONALLY BLANK]
<PAGE>

     IN WITNESS WHEREOF, each of the undersigned has caused this Amendment to be
executed and delivered by its duly authorized officer as of the date first above
written.



                             D&K RECEIVABLES CORPORATION


                             By:  /s/ Thomas S. Hilton
                                      ----------------
                             Name:    Thomas S. Hilton
                                      ----------------
                             Title:   Senior Vice President & CFO
                                      ---------------------------



                             D&K HEALTHCARE RESOURCES, INC.


                             By:  /s/ Thomas S. Hilton
                                      ----------------
                             Name:    Thomas S. Hilton
                                      ----------------
                             Title:   Senior Vice President & CFO
                                      ---------------------------



                             BLUE KEEL FUNDING, LLC, as Purchaser


                             By:  /s/ Bernard J. Angelo
                                      -----------------
                             Name:    Bernard J. Angelo
                                      -----------------
                             Title:   Vice President
                                      --------------



                             FLEET NATIONAL BANK, as the Administrator


                             By:  /s/ Paul Schmieder
                                      --------------
                             Name:    Paul Schmieder
                                      --------------
                             Title:   Vice President
                                      --------------