<PAGE>
                                                                     Exhibit 4.8


                                                                  EXECUTION COPY

                        SECOND AMENDMENT dated as of March 25, 2000 (this
                  "Amendment"), to the Amended and Restated Credit Agreement
                  dated as of November 6, 1998, as amended by the Waiver and
                  First Amendment dated as of February 7, 2000 (as amended by
                  the First Amendment and Consent dated as of March 15, 2000 and
                  the Second Amendment dated as of March 24, 2000) (the "Credit
                  Agreement"), among SCHEIN PHARMACEUTICAL, INC., a Delaware
                  corporation (the "Borrower"), the lenders party hereto (the
                  "Lenders") and THE CHASE MANHATTAN BANK, a New York banking
                  corporation, as administrative agent for the Lenders (in such
                  capacity, the "Administrative Agent"), as issuing bank and as
                  collateral agent.

            A. Pursuant to the Credit Agreement, the Lenders and the Issuing
Bank have extended credit to the Borrower, and have agreed to extend credit to
the Borrower, in each case pursuant to the terms and subject to the conditions
set forth therein.

            B. The Borrower has requested that the Credit Agreement be amended
as set forth herein.

            C. The Required Lenders are willing to amend the Credit Agreement
pursuant to the terms and subject to the conditions set forth herein.

            D. Capitalized terms used and not otherwise defined herein shall
have the meanings assigned to them in the Credit Agreement.

            In consideration of the premises and the agreements, provisions and
covenants herein contained, the parties hereto hereby agree, on the terms and
subject to the conditions set forth herein, as follows:

            SECTION 1. Certain Amendments to Credit Agreement.

            (a) Section 1.01 of the Credit Agreement is hereby amended as
follows:

                  (i) by inserting the following sentence at the end of the
            definition of "Net Income":

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                                                                               2


                  "For the fiscal quarter ended (i) December 25, 1999, Net
                  Income shall be determined without giving effect to a
                  restructuring charge in a pre-tax amount not to exceed
                  $87,000,000 to be recorded by the Borrower as of December 25,
                  1999 and (ii) March 25, 2000, Net Income shall be determined
                  without giving effect to a severance charge in a pre-tax
                  amount not to exceed $3,500,000 to be recorded by the Borrower
                  as of March 25, 2000.".

                  (ii) by inserting the following sentence at the end of the
            definition of "Net Worth":

                  "Notwithstanding the foregoing, for the fiscal quarter ended
                  (i) December 25, 1999, Net Worth shall be determined without
                  giving effect to a restructuring charge in an after-tax amount
                  not to exceed $52,200,000 and (ii) March 25, 2000, Net Worth
                  shall be determined without giving effect to a severance
                  charge in an after-tax amount not to exceed $2,500,000.".

            (b) Section 6.14 of the Credit Agreement is hereby amended and
restated in its entirety as follows:

            "SECTION 6.14. Leverage Ratio. Permit the Leverage Ratio as of any
date during any period specified below to be in excess of the ratio set forth
below next to such period:

                  Period                                  Ratio
                  ------                                  -----

            From and including the last day of
            fiscal 1996 to but excluding the
            last day of the second fiscal
            quarter of 1997                           6.50 to 1.00

            From and including the last day of
            the second fiscal quarter of 1997
            to but excluding the last day of
            the third fiscal quarter of 1997          6.00 to 1.00

            From and including the last day of
            the third fiscal quarter of 1997 to
            but excluding the last day of
            fiscal 1997                               5.75 to 1.00

            From and including the last day of
            fiscal 1997 to but excluding the
            last day of the second fiscal
            quarter of 1998                           5.25 to 1.00

            From and including the last day of
            the second fiscal quarter of 1998
            to but excluding the last day of          5.00 to 1.00
            the third fiscal quarter of 1998

            From and including the last day of
            the third fiscal quarter of 1998 to
            and including the last day of
            fiscal 1998                               4.50 to 1.00

<PAGE>
                                                                               3


            From and including the first day of
            fiscal 1999 to but excluding the
            last day of the third fiscal
            quarter of 1999                           5.00 to 1.00

            From and including the last day of
            the third fiscal quarter of 1999 to
            and including the last day of
            fiscal 1999                               4.25 to 1.00

            From and including the first day of
            the first fiscal quarter of 2000 to
            and including the last day of the
            first fiscal quarter of 2000              5.60 to 1.00

            From and including the first day of
            the second fiscal quarter of 2000
            to and including the last day of
            the second fiscal quarter of 2000         5.60 to 1.00

            From and including the first day of
            the third fiscal quarter of 2000 to
            and including the last day of the
            third fiscal quarter of 2000              4.50 to 1.00

            From and including the first day of
            the fourth fiscal quarter of 2000
            to and including the last day of
            the fourth fiscal quarter of 2000         3.50 to 1.00

            Thereafter                                3.50 to 1.00".

            (c) Section 6.16 of the Credit Agreement is hereby amended and
restated in its entirety as follows:

                  "SECTION 6.16. Working Capital. Permit the ratio of Current
      Assets to Current Liabilities as of the last day of any fiscal quarter
      ending (i) at or before the end of fiscal 2000 to be less than 1.50 to
      1.00, or (ii) after the end of fiscal 2000 to be less than 1.75 to 1.00,
      provided that Indebtedness incurred under the Senior Floating Rate Notes
      shall in no event be classified as Current Liabilities for purposes of
      this Section.".

            (d) Section 6.17 of the Credit Agreement is hereby amended and
restated in its entirety as follows:

                  "SECTION 6.17. Fixed Charge Coverage Ratio. Permit the Fixed
      Charge Coverage Ratio as of any date during any period specified below to
      be less than the ratio set forth below next to such period:

                  Period                                  Ratio
                  ------                                  -----

            From and including the last day of
            fiscal 1996 to but excluding the
            last day of                               1.00 to 1.00

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                                                                               4


            fiscal 1997

            From and including the last day of
            fiscal 1997 to and including the          1.10 to 1.00
            last day of fiscal 1998

            From and including the first day of
            fiscal 1999 to but excluding the
            last day of the second fiscal
            quarter of 1999                           0.75 to 1.00

            From and including the last day of
            the second fiscal quarter of 1999
            to but excluding the last day of
            the third fiscal quarter of 1999          0.80 to 1.00

            From and including the last day of
            the third fiscal quarter of 1999 to
            and including the last day of
            fiscal 1999                               0.90 to 1.00

            From and including the first day of
            the first fiscal quarter of 2000 to
            and including the last day of the
            first fiscal quarter of 2000              0.50 to 1.00

            From and including the first day of
            the second fiscal quarter of 2000
            to and including the last day of
            the second fiscal quarter of 2000         0.50 to 1.00

            From and including the first day of
            the third fiscal quarter of 2000 to
            and including the last day of the
            third fiscal quarter of 2000              0.50 to 1.00

            From and including the first day of
            the fourth fiscal quarter of 2000
            to and including the last day of
            the fourth fiscal quarter of 2000         0.60 to 1.00

            Thereafter                               1.50 to 1.00".

            (e) Section 6.18 of the Credit Agreement is hereby amended and
restated in its entirety as follows:

                  "SECTION 6.18. Interest Expense Coverage Ratio. Permit the
      Interest Expense Coverage Ratio as of any date during any period specified
      below to be less than the ratio set forth below next to such period:

                  Period                                  Ratio
                  ------                                  -----

            From and including the last day of
            the third fiscal quarter of 1998 to
            and including the last day of
            fiscal 1998                               2.50 to 1.00

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                                                                               5


            From and including the first day of
            fiscal 1999 to and including the
            last day of the second fiscal
            quarter of 1999                           2.25 to 1.00

            From and including the first day of
            the third fiscal quarter of 1999 to
            and including the last day of the
            third fiscal quarter of 1999              2.50 to 1.00

            From and including the first day of
            the fourth fiscal quarter of 1999
            to and including the last day of
            the fourth fiscal quarter of 1999         2.75 to 1.00

            From and including the first day of
            the first fiscal quarter of 2000 to
            and including the last day of the
            first fiscal quarter of 2000              1.80 to 1.00

            From and including the first day of
            the second fiscal quarter of 2000
            to and including the last day of
            the second fiscal quarter of 2000         1.80 to 1.00

            From and including the first day of
            the third fiscal quarter of 2000 to
            and including the last day of the
            third fiscal quarter of 2000              2.00 to 1.00

            From and including the first day of
            the fourth fiscal quarter of 2000
            to and including the last day of
            the fourth fiscal quarter of 2000         2.50 to 1.00

            Thereafter                                2.75 to 1.00".

                  SECTION 2. Certain Agreements of the Company. (a) For purposes
      of this Section, "Additional Financing" shall mean any combination of
      committed credit facilities, equity, junior-lien financing, asset sales
      (provided that such sale complies with the terms of the Credit Agreement)
      and subordinated debt obtained no later than May 1, 2000, in an aggregate
      amount of at least $40,000,000 with a maturity of no sooner than January
      2, 2001 and otherwise on terms reasonably satisfactory to the Required
      Lenders.

            (b) The Borrower agrees to pay to each Lender, through the
      Administrative Agent, on the Effective Date, an amendment fee (i) equal to
      0.25% of the sum of such Lender's outstanding Term Loan and Revolving
      Credit Commitment (whether used or unused on such date), provided that
      such Lender shall have executed this Amendment on or prior to 3:00 p.m.,
      New York City time, on March 31, 2000, and (ii) with respect to any Lender
      not subject to clause (i) above, 0.125% of the sum of such Lender's
      outstanding Term Loan and Revolving Credit Commitment (whether used or
      unused on such date) ((i) and (ii), collectively, the "Amendment Fee").

<PAGE>
                                                                               6


            (c) In the event that the Borrower does not obtain the Additional
      Financing, the Borrower agrees as follows:

            (i) Notwithstanding the definition of "Applicable Percentage" or any
            other provision of the Credit Agreement, the Borrower agrees that
            (i) the "Eurodollar Spread" shall be (w) 3.500% from the Effective
            Date through April 30, 2000, (x) 4.000% from May 1, 2000 through
            August 31, 2000, (y) 4.250% from September 1, 2000 through December
            31, 2000, and (z) 4.500% thereafter and (ii) the "ABR Spread" shall
            be (w) 2.500% from the Effective Date through April 30, 2000, (x)
            3.000% from May 1, 2000 through August 31, 2000, (y) 3.250% from
            September 1, 2000 through December 30, 2000, and (z) 3.500%
            thereafter.

            (ii) The Borrower agrees that it shall pay to each Lender, through
            the Administrative Agent, on May 1, 2000, a fee equal to 0.50% of
            the sum of such Lender's outstanding Term Loan and Revolving Credit
            Commitment (whether used or unused on such date).

            (iii) The Borrower agrees that it shall pay to each Lender, through
            the Administrative Agent, on September 1, 2000, a fee equal to 0.25%
            of the sum of such Lender's outstanding Term Loan and Revolving
            Credit Commitment (whether used or unused on such date).

            (iv) The Borrower agrees that it shall pay to each Lender, through
            the Administrative Agent, on December 31, 2000, a fee equal to 0.25%
            of the sum of such Lender's outstanding Term Loan and Revolving
            Credit Commitment (whether used or unused on such date).

            (d) In the event that the Borrower does obtain the Additional
      Financing, the Borrower agrees as follows:

            (i) Notwithstanding the definition of "Applicable Percentage" or any
            other provision of the Credit Agreement, the Borrower agrees that
            (i) the "Eurodollar Spread" shall be (x) 3.500% from the Effective
            Date through August 31, 2000, (y) 4.000% from September 1, 2000
            through December 31, 2000, and (z) 4.250% thereafter and (ii) the
            "ABR Spread" shall be (x) 2.500% from the Effective Date through
            August 31, 2000, (y) 3.000% from September 1, 2000 through December
            30, 2000, and (z) 3.250% thereafter.

            (ii) The Borrower agrees that it shall pay to each Lender, through
            the Administrative Agent, on September 1, 2000, a fee equal to 0.25%
            of the sum of such Lender's outstanding Term Loan and Revolving
            Credit Commitment (whether used or unused on such date).

            (iii) The Borrower agrees that it shall pay to each Lender, through
            the Administrative Agent, on December 31, 2000, a fee equal to 0.25%
            of the sum of such Lender's outstanding Term Loan and Revolving
            Credit Commitment (whether used or unused on such date).

<PAGE>
                                                                               7


            (e) The Borrower agrees to use its best efforts promptly to obtain
      the Additional Financing.

            (f) The Borrower agrees, not later than two weeks after the end of
      each month, to deliver to the Administrative Agent, (i) a three-month
      projection of cash flows with respect to the Borrower and its consolidated
      Subsidiaries, with weekly projections for the first month of the
      forecasting period and monthly projections for the second and third months
      of the forecasting period and (ii) concurrently with the delivery of the
      projections referred to in clause (i), a statement reconciling the
      previous months' actual cash flows with the projections previously
      delivered for that month.

            (g) Without limiting the obligations of the Borrower under Section
      9.05 of the Credit Agreement, the Borrower agrees from time to time upon
      demand to pay the reasonable fees and the out-of-pocket expenses of (i)
      financial advisors retained by the Administrative Agent on behalf of the
      Lenders and (ii) such additional counsel, including, without limitation,
      Wachtell, Lipton, Rosen & Katz, and other consultants as the
      Administrative Agent shall deem it advisable to retain to provide advice
      to the Administrative Agent and the Lenders.

                  SECTION 3. Representations and Warranties. The Borrower
      represents and warrants to each of the Lenders and the Administrative
      Agent that:

                  (i) After giving effect to this Amendment, the representations
            and warranties set forth in Article III of the Credit Agreement are
            true and correct in all material respects with the same effect as if
            made on and as of the date hereof.

                  (ii) After giving effect to this Amendment, no Event of
            Default or Default has occurred and is continuing.

                  SECTION 4. Conditions to Effectiveness of Amendments. The
      amendments set forth herein shall become effective as of the date of this
      Amendment, but only upon the satisfaction of the following conditions (the
      date on which the last of such conditions is satisfied being called the
      "Effective Date"):

                  (a) the Administrative Agent shall have received counterparts
            of this Amendment that, when taken together, bear the signatures of
            the Borrower and the Required Lenders;

                  (b) the Administrative Agent shall have received in
            immediately available funds the Amendment Fee referred to in Section
            2; and

                  (c) the representations and warranties set forth in Section 3
            shall be true and correct.

                  SECTION 5. Credit Agreement. Except as expressly set forth
      herein, this Amendment shall not by implication or otherwise limit,
      impair, constitute a waiver of, or otherwise affect the rights and
      remedies of the Lenders and the Administrative Agent under the Credit
      Agreement, or alter, modify, amend or in any way affect any of the terms,
      conditions, obligations, covenants or agreements contained in the Credit
      Agreement, all of which are ratified and affirmed in all respects and
      shall continue in full force and effect. This Amendment shall apply and be
      effective only with respect to the

<PAGE>
                                                                               8


      provisions of the Credit Agreement specifically referred to herein. The
      agreements set forth in this Amendment shall be deemed for all purposes to
      be covenants contained in Article VI of the Credit Agreement as amended
      hereby, and the failure of the Borrower to perform any of such agreements
      in accordance with the terms thereof shall constitute an Event of Default
      under the Credit Agreement as so amended. This Amendment shall constitute
      a "Loan Document" for all purposes of the Credit Agreement and the other
      Loan Documents.

                  SECTION 6. Expenses. The Borrower agrees to reimburse the
      Administrative Agent for (a) the fees and expenses referred to in Section
      2 and (b) its out-of-pocket expenses reasonably incurred in connection
      with this Amendment, including the reasonable fees, charges and
      disbursements of Cravath, Swaine & Moore, counsel for the Administrative
      Agent.

                  SECTION 7. Applicable Law. THIS AMENDMENT SHALL BE GOVERNED
      BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

<PAGE>
                                                                               9


                  SECTION 8. Counterparts. This Amendment may be executed in two
      or more counterparts, each of which shall constitute an original but all
      of which when taken together shall constitute but one contract. Delivery
      of an executed counterpart of a signature page of this Amendment by
      facsimile shall be effective as delivery of a manually executed
      counterpart of this Amendment.

                  IN WITNESS WHEREOF, the parties hereto have caused this
      Amendment to be duly executed by their respective authorized officers as
      of the day and year first written above.

                                        SCHEIN PHARMACEUTICAL, INC.,

                                        by

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

<PAGE>

                                        THE CHASE MANHATTAN BANK, individually
                                        and as Administrative Agent, Collateral
                                        Agent and Issuing Bank,


                                        by

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

<PAGE>

                                        THE BANK OF NOVA SCOTIA,

                                        by


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

<PAGE>

                                        BANK OF TOKYO-MITSUBISHI TRUST COMPANY,

                                        by


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

<PAGE>

                                        BAYERISCHE HYPOTHEKEN-UND WECHSEL-BANK
                                        AKTIENGESSELLSCHAFT, NEW YORK BRANCH,

                                        by


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

                                        by


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

<PAGE>

                                        COMERICA BANK,

                                        by


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

<PAGE>

                                        COMMERCIAL LOAN FUNDING TRUST I,

                                                    by: LEHMAN COMMERCIAL PAPER,
                                                    INC., not in its individual
                                                    capacity but solely as
                                                    Administrative Agent

                                        by


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

<PAGE>


                                        COOPERATIEVE CENTRALE RAIFFEIFEN-
                                        BOERENLEENBANK, B.A., "RABOBANK
                                        NEDERLAND", NEW YORK BRANCH,

                                        by

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

                                        by

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

<PAGE>

                                        DEUTSCHE BANK, A.G., NEW YORK AND/OR
                                        CAYMAN ISLAND BRANCHES,

                                        by

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

                                        by

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

<PAGE>

                                        DG BANK DEUTSCHE
                                        GENOSSENSCHAFTSBANK, CAYMAN
                                        ISLAND BRANCH,

                                        by


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

                                        by


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

<PAGE>

                                        FIRST UNION NATIONAL BANK,

                                        by


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

<PAGE>


                                        FLEET BANK, N.A. (formerly known as
                                        NatWest Bank, N.A.),

                                        by

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

<PAGE>

                                        KEYBANK NATIONAL ASSOCIATION,

                                        by

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


<PAGE>

                                        MELLON BANK, N.A.,

                                        by


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

<PAGE>


                                        PNC BANK, N.A.,

                                        by

                                            ------------------------------------
                                            Name:
                                            Title:
<PAGE>

                                        SOCIETE GENERALE, NEW YORK BRANCH,

                                        by

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


<PAGE>

                                        SUMMIT BANK,

                                        by


                                            ------------------------------------
                                            Name:
                                            Title:
<PAGE>

                                        AG CAPITAL FUNDING PARTNERS, L.P.,

                                        by


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

<PAGE>

                                        BEAR STEANS & CO. INC.,

                                        by


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