<PAGE>
                                                                   Exhibit 10.67

AS EXECUTED
-----------

                        CONFIDENTIAL TREATMENT REQUESTED
                        --------------------------------

         AMENDMENT NUMBER 3 TO DEVELOPMENT, LICENSE AND SUPPLY AGREEMENT

     This Amendment to the Development, License, Supply Agreement (the
"Amendment") is effective as of the 19th day of May 1999 between Elan
Corporation plc, a corporation organized under the laws of Ireland ("Elan") and
Schein Pharmaceutical, Inc., a Delaware corporation ("Schein").

                                  INTRODUCTION

     A. Elan and Schein entered into a Development, License and Supply
Agreement, dated March 31, 1998, as amended by Amendment Number 1 and Amendment
Number 2 to the Development, License and Supply Agreement (the "Agreement").

     B. The parties wish to amend the Agreement in accordance with the terms of
this Amendment.

     NOW, THEREFORE, in consideration of the mutual covenants and promises
herein contained, and for other good and valuable consideration, it is agreed as
follows:

     1. DEFINITIONS AND INCORPORATION.

     1.1. Unless otherwise defined, all terms used herein shall have the meaning
ascribed to them in the Agreement, and the terms and provisions of the Agreement
are incorporated herein by reference as though set forth in full.

     1.2. In this Amendment unless the context otherwise requires:

* shall mean * of *.

* Settlement Agreement shall mean the Settlement Agreement and Release
dated * between Elan and *.

* Suit shall mean the civil complaint which was prosecuted by Elan against *
in the * captioned * Elan * Settlement Agreement) whereby, inter alia,

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

<PAGE>

(i)  Elan * Elan's *; and

(ii) * Elan's * verapamil * to * Elan.

Branded Verapamil shall mean a pharmaceutical product containing sustained
release formulations of verapamil hydrochloride in dosage strengths of 120
milligrams, 180 milligrams, 240 milligrams and 360 milligrams which is
manufactured by Elan under its NDA 19-614 and is marketed under (i) the
* or (ii) any other brand name. Branded Verapamil shall not include Generic
Verapamil (as defined below).

First Generic shall mean the first generic A Rated substitute product for
* in the Territory.

* shall mean * of *.

* Settlement Agreement shall mean the Settlement Agreement, dated *, between *
and Elan.

* Suit shall mean the civil action which was prosecuted by Elan and * against
* in the United States District Court for the * alleging that * infringed
Elan's U.S. Patent No. *.

* shall mean * of *.

* shall mean Branded Verapamil marketed under the * brand name.

     2. AMENDMENTS. The parties agree as follows with respect to the
pharmaceutical product containing sustained release formulations of verapamil
hydrochloride in dosage strengths of 120 milligrams, 180 milligrams, 240
milligrams and 360 milligrams manufactured by Elan under its NDA 19-614
("Generic Verapamil"):

          2.1. Generic Verapamil shall be included in the definition of "DSDF"
(and thereby also included in the definition of "Product") under the terms and
conditions of the Agreement provided however, that the exclusive license granted
to Schein for Generic Verapamil pursuant to Clause 2.1 of the Agreement shall be
limited to generic prescription use in the Territory. For the avoidance of
doubt, Schein shall have no rights (i) to sell Generic Verapamil as a Branded
Verapamil for prescription or over the counter non-prescription use in the
Territory, or (ii) to sell Generic Verapamil for over the counter
non-prescription use in the Territory.

          2.2. With respect to Generic Verapamil, the Parties hereby expressly
agree that

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

                                       2

<PAGE>

Clauses 3.2, 3.3.2, 3.3.3, 3.3.4, 3.3.5, 3.3.6 and 10.3 of the Agreement
shall not apply and have no force or effect.

          2.3. Subject to the provisions of Clauses 2.4 and 2.5 of this
Amendment, Elan, at its option, shall be entitled to institute proceedings for
any alleged Defense Infringement or Enforcement Infringement in respect of any
infringements of the Elan Patent Rights with respect to Generic Verapamil at its
own expense and for its own benefit. In the event that Elan does not wish to
institute such enforcement or defense proceedings, Elan has granted * the
right, at its option and at its sole discretion, subject to the provisions of
Clauses 2.4 and 2.5 of this Amendment, to institute enforcement or defense
proceedings at its own expense and for its own benefit. In the event that Elan
or * does not wish to institute such enforcement or defense proceedings,
Elan shall promptly notify Schein of such decision and Schein shall, at its
option and at its sole discretion, subject to the provisions of Clauses 2.4 and
2.5 of this Amendment, have the right to institute enforcement or defense
proceedings at its own expense and for its own benefit. The non litigating Party
shall cooperate with the other Party.

          2.4. * SETTLEMENT AGREEMENT

               2.4.1. Pursuant to the * Settlement Agreement, Elan and
* settled the * Suit, and Elan * Elan's * verapamil * verapamil *.

               2.4.2. *, Elan * Elan's * verapamil * Elan *, Elan *.

               2.4.3. Schein acknowledges Elan's covenants as described in
Clauses 2.4.1. and 2.4.2. and agrees to be bound, and (where applicable) to
cause any of its subsequent assignees and exclusive licensees to be bound, by
the covenant * Schein * Schein * Elan's * verapamil *. For the avoidance of
doubt, Schein's rights to bring any such defense proceedings shall be subject
to the prior rights of Elan and * as set out in Clause 2.3.

               2.4.4. At the request of Elan, Schein shall (and shall procure
that any other necessary parties shall) execute and deliver all such documents,
acts and things with Elan,

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

                                       3

<PAGE>

* or any third party as may reasonably be required subsequent to the signing
of this Agreement to give effect to Schein' agreement under Clause 2.4.3.

               2.4.5. Elan acknowledges that pursuant to the * Settlement
Agreement, * Elan * Elan * verapamil * Elan * verapamil *. Elan * Elan *
verapamil * Elan.

          2.5. * SETTLEMENT AGREEMENT

               2.5.1. Pursuant to the * Settlement Agreement, Elan and *
settled the * Suit, and Elan * Elan's * verapamil *.

               2.5.2. *, Elan *.

               2.5.3. Schein acknowledges Elan's covenants as described in
Clauses 2.5.1. and 2.5.2. and agrees to be bound, and (where applicable) to
cause any of its subsequent assignees and exclusive licensees to be bound, by
the covenant * Schein * Schein * Elan's * verapamil *. For the avoidance of
doubt, Schein's rights to bring any such defense proceedings shall be subject
to the prior rights of Elan and * as set out in Clause 2.3.

               2.5.4. At the request of Elan, Schein shall (and shall procure
that any other necessary parties shall) execute and deliver all such documents,
acts and things with Elan, * or any third party as may reasonably be required
subsequent to the signing of this Agreement to give effect to Schein's
agreement under Clause 2.5.3.

               2.5.5. Elan * Elan * Elan * Elan's *.

          2.6. Elan has licensed * to sell * in the Territory. The said

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

                                       4

<PAGE>

licence excludes the right of * to provide for, market or sell a generic
substitute of *. Schein hereby acknowledges and confirms that Clause 4.3 of
the Agreement shall in no way restrict Elan or * from selling * in the
Territory.

          2.7. * shall be payable to Elan for Generic Verapamil under the
Agreement, including, without limitation, the cost for Pivotal Bio PK Study,
pharmacokinetic studies and related assays, stability data generation,
clinical studies and compilation and submission of dossiers required for
registration, and market pack stability studies. Furthermore, in no event,
shall Elan shall be obliged to incur any such development fees or perform any
development work on Generic Verapamil.

          2.8. Elan has secured FDA Approval for Verelan and shall be
responsible for submitting the filing with the FDA to seek approval to appoint
Schein as the distributor of Generic Verapamil in the Territory under the
* FDA Approval. Schein shall co-operate and provide all reasonable assistance
to Elan in obtaining such appointment. In the event that Schein packages
Generic Verapamil, Schein shall be responsible for obtaining all FDA and
other approvals necessary for Schein to package Generic Verapamil into final
market packaging, and to provide Elan with the appropriate documentation
relating to the packaging section of the * FDA Approval.

          2.9. Elan and Schein shall confer on the manufacture of Launch Stocks
and all related matters associated with the launch of Generic Verapamil in the
Territory provided however, that notwithstanding the foregoing, Schein shall be
obliged in any event to market Generic * within * of the first commercial sale
of the First Generic in the Territory, and provided further, that Schein
shall have received in advance of such launch, an agreed quantity of Launch
Stocks of Generic Verapamil in final market packaged form with the Schein
label. The provisions of Clauses 8.7 and 9 of the Agreement shall be amended
in accordance with this paragraph with respect to Generic Verapamil but only
to the extent that any such provisions conflict with this paragraph.

          2.10. The Parties agree that delivery of consignments of Generic
Verapamil shall be effected by Elan FOB Gainesville, Georgia. The Parties shall
agree whether Generic Verapamil is to be supplied by Elan in bulk or final
market packaged form with the Schein label. If the Generic Verapamil is to be
supplied in bulk form, Schein shall be responsible for the packaging of Generic
Verapamil into final market packaging.

          2.11. In consideration of the license of the Elan Patent Rights
granted to Schein under this Amendment, Schein shall pay to Elan a * license
fee with respect to Generic Verapamil in the aggregate amount of *, which
shall be due upon the Date of First Commercial Sale of Generic Verapamil in
the Territory. For the avoidance of doubt, Schein shall have no further
obligation * for Generic Verapamil. The provisions of Clause 10.2 of the
Agreement shall not apply and have no force or effect with respect to Generic
Verapamil.

          2.12. In the event that Generic Verapamil is supplied by Elan to
Schein in final

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

                                       5

<PAGE>

market packaged form, such Product shall be supplied to Schein at *. For the
avoidance of doubt, in such event, * shall include the fully allocated costs
of packaging Generic Verapamil into final market packaged form.

          2.13. In the event that Generic Verapamil is supplied by Elan to
Schein in bulk form, such Product shall be supplied to Schein at * provided
however, that any costs incurred by Schein in packaging Generic Verapamil
into final market packaged form shall not be a deductible expense in
calculating the Profit for Generic Verapamil.

          2.14. Subject to the following sentence, Elan shall be entitled to
receive a royalty of * of the Profit of Generic Verapamil in accordance with
Clause 10.5 of the Agreement. In the event that Schein fails to market Generic
Verapamil within * of commercial sale of the First Generic solely due to
the failure of Elan to supply launch stocks of Generic Verapamil to Schein in
accordance with Clause 2.9 hereof, the royalty payable to Elan on Generic
Verapamil shall be * of Profit.

          2.15. In addition to the rights of termination provided for in Clauses
12.3, 12.4 (other than Clause 12.4.4 for which this Clause 2.15 is substituted
in lieu thereof as regards Generic Verapamil only) and elsewhere in the
Agreement, in the event that the net price payable to Elan for Generic Verapamil
(that is the price of Generic Verapamil and the percentage of Profit) is, or
in Elan's reasonable opinion is likely to be, less than * for Generic
Verapamil, then Elan shall be entitled to terminate the license granted to
Schein for Generic Verapamil under this Amendment, provided however, such
termination right may only be exercised after the cumulative Profit retained
by Schein on sales of Generic Verapamil (after payment of the royalty due to
Elan with respect to such sales pursuant to Clause 10.5 of the Agreement), is
equal to, or greater than, *.

     3. REAFFIRMATION OF THE AGREEMENT AND OTHER DOCUMENTS. Except as modified
herein, all of the covenants, terms and conditions of the Agreement, and all
documents, instruments and agreements executed in conjunction therewith remain
in full force and effect and are hereby ratified and reaffirmed in all respects.
In the event of any conflict, inconsistency or incongruity between the terms and
conditions of this Amendment and the covenants, terms and conditions of the
Agreement or any documents, instruments or agreements executed in conjunction
therewith, the terms and conditions of this Amendment shall govern and control.

     4. COUNTERPARTS. This Amendment may be executed in two or more
counterparts, each of which together shall constitute an original but which,
when taken together, shall constitute but one instrument.

     IN WITNESS WHEREOF, this Amendment is executed as of the day and year first
above written.

----------
*    Material omitted pursuant to a request for confidential treatment. The
     omitted material has been filed separately with the Securities and Exchange
     Commission.

                                       6

<PAGE>

                              ELAN CORPORATION, PLC

                              By:  /s/ Seamus Mulligan
                                   ------------------------------------
                              Name: Seamus Mulligan
                                    -----------------------------------
                              Title: Illegible
                                     ----------------------------------


                              SCHEIN PHARMACEUTICAL, INC.

                              By:  /s/ Paul Kleutghen
                                   ------------------------------------
                              Name: Paul Kleutghen
                                    -----------------------------------
                              Title: Senior Vice President
                                     ----------------------------------