<PAGE>

                                                                 Exhibit 10.15.3

Record and Return to:
Clinton A. Poff, Esq.
Poff & Bowman LLC
P.O. Box 24
Hawthorne, New Jersey 07507

                        MORTGAGE MODIFICATION AGREEMENT
                        -------------------------------

     This Agreement made as of the first day of May 2001 between

     PAR PHARMACEUTICAL, INC., a New Jersey corporation, located at 1 Ram Ridge
Road, Spring Valley, New York 10977 (the "Borrower"); and

     HUDSON UNITED BANK, a New Jersey corporation, having its administrative
headquarters at 1000 MacArthur Boulevard, Mahwah, New Jersey 07430, successor in
interest to Urban National Bank (the "Bank");

                              W I T N E S S E T H:
                              -------------------

     WHEREAS:

     A.   The Borrower executed and delivered to the Bank its promissory note in
the original principal amount of $1,340,000.00 dated May 4, 1994 (the "Note");

     B.   Such Note is secured by a mortgage dated May 4, 1994 on property
commonly known as 2 Ram Ridge Road, shown and designated as Lot 1 on a certain
map entitled "Subdivision Map Prepared For Ramapo Development Assoc., Town of
Ramapo, Rockland County, New York," made by Ostertag & McDougall, Surveyors,
dated August 9, 1974, last revised December 20, 1974, and filed in the Rockland
County Clerk's Office on January 14, 1975 as Map No. 4585, which mortgage was
recorded in the Rockland County Registrar's Office on May 13, 1994 in Liber 708
Page 1803, etc (the "Mortgage");

     C.   The outstanding principal balance of the mortgage obligation is
$876,662.81; and

     D.   The Borrower has requested and the Bank has agreed to extend the
maturity date of the Note secured by the Mortgage from "May 1, 2001" to "May 1,
2014" and to make certain other modifications and amendments to the Note and
Mortgage as set forth herein.

     NOW, THEREFORE, in consideration of the above premises and for other good
and valuable consideration, the receipt of which is hereby acknowledged, the
parties agree as follows:

     1.   Notwithstanding anything to the contrary set forth in the Mortgage,
the maturity date of the Note is changed from "May 1, 2001" to "May 1, 2014."

     2.   Further, the interest rate payable on the Note for the period from May
1, 2001 through and including April 30, 2006 shall be eight and one-half (8-1/2)
percent; commencing May 1, 2006 through and including April 30, 2011 the
interest rate payable on the Note shall be at a fixed rate of interest equal to
325 basis points above the interest rate charged by the Federal Home Loan Bank
Board of New York on mortgage loans having a maturity of five (5) years rounded
up to the nearest one-eighth of one (1/8) percent in effect forty-five (45) days
before May 1, 2006; and commencing from May 1, 2011 and continuing until the
Note is paid in full the interest rate payable on the Note shall be at a fixed
rate of interest equal to 325 basis points above the interest rate charged by
the Federal Home Loan Bank Board of New York on mortgage loans having a maturity
of five (5) years rounded up to the nearest one-eighth of one (1/8) percent in
effect forty-five (45) days before May 1, 2011.

     3.   The Borrower shall be responsible for any and all fees incurred by the
Bank in connection with the transactions contemplated by this Agreement
including, without limitation, any mortgage recording tax and the fees and
disbursements of the Bank's counsel.
<PAGE>

     4.   The Borrower does hereby affirm and ratify the extent and validity of
the Note, the Mortgage and all other documents executed by the Borrower
including, but not limited to, any and all commitment letters (all such
documents being herein collectively referred to as, the "Loan Documents"). The
Borrower hereby confirms that such Loan Documents remain in full force and
effect as of the date hereof. The Borrower does hereby represent, warrant and
confirm that there are no defenses, set-offs, rights, claims or causes of action
of any nature whatsoever which the Borrower has or may assert against the Bank
with respect to the Note, the Mortgage securing such Note and/or any of the
other Loan Documents.

     5.   The undersigned Borrower and Guarantor by executing this Agreement,
with respect to any claims arising prior to the date of the execution of this
Agreement, expressly waives any and all right to assert a claim, counterclaim or
defense against the Bank arising out of or in any way connected with the
mortgage transaction between the Bank and the Borrower relating to the mortgaged
premises, whether such claim, counterclaim or defense now exists. The foregoing
waiver shall apply to any action instituted by any of the undersigned and to any
action or proceeding brought against any of the undersigned by the Bank
including, without limitation, any action brought in connection with any
guarantee executed in connection with the Mortgage.

     6.   THE UNDERSIGNED BORROWER BY EXECUTING THIS DOCUMENT ACKNOWLEDGES THAT
ITS HAS HAD FULL AND FAIR OPPORTUNITY TO REVIEW THIS AGREEMENT AND THE DOCUMENTS
REFERRED TO HEREIN WITH INDEPENDENT COUNSEL OF ITS CHOICE AND THAT IT HAS BEEN
INDEPENDENTLY ADVISED AS TO THEIR TERMS AND CONDITIONS WHICH ARE ACCEPTABLE TO
IT. FURTHER, IT CONFIRMS THAT IN DELIVERING THIS AGREEMENT TO THE BANK, IT IS
NOT RELYING ON ANY PROMISE, COMMITMENT, REPRESENTATION OR UNDERSTANDING, EITHER
EXPRESS OR IMPLIED, MADE BY OR ON BEHALF OF THE BANK THAT IS NOT EXPRESSLY SET
FORTH HEREIN, THE EXISTING MORTGAGE DOCUMENTS OR THE DOCUMENTS REFERRED TO
HEREIN. THE BORROWER BY EXECUTING THIS AGREEMENT ACKNOWLEDGES AND UNDERSTANDS
THAT ALL OBLIGATIONS UNDER THE NOTE AND THE MORTGAGE ARE DUE AND PAYABLE ON MAY
1, 2014, UNLESS THE BANK, IN ITS SOLE AND ABSOLUTE DISCRETION, EXTENDS THE
MATURITY DATE OF SUCH OBLIGATION AND THAT THE BANK HAS NOT MADE ANY
REPRESENTATION THAT IT WILL EXTEND THE MATURITY DATE OF SUCH OBLIGATION.

     7.   This Agreement shall be binding on the parties hereto and their
successors and assigns or heirs and personal representatives, as the case may
be.

     IN WITNESS WHEREOF, the parties have executed this document the day and
year first above written.

WITNESS:                                  PAR PHARMACEUTICAL, INC.


/s/ Peter H. Streelman                    by /s/ Dennis J. O'Connor
----------------------                       ----------------------
                                             Dennis J. O'Connor
                                             Vice President, CFO and
                                             Secretary

WITNESS:                                     HUDSON UNITED BANK


/s/ Kristen Hamilton                      by /s/ Peter H. Streelman
--------------------                         ----------------------
                                             Peter H. Streelman
                                             Senior Vice President

<PAGE>

     The undersigned guarantor of performance and payment does hereby approve
all of the terms of this agreement, does hereby approve the execution and
delivery of the agreement by Par Pharmaceutical, Inc. and does hereby
acknowledge and confirm its continuing liability and responsibility to Hudson
United Bank, with respect to the debt referred to in the agreement in accordance
with its guaranty.


WITNESS:                              PHARMACEUTICAL RESOURCES, INC.


/s/ Peter H. Streelman             by /s/ Dennis J. O'Connor
----------------------                ----------------------
                                      Dennis J. O'Connor
                                      Vice President, CFO and
                                      Secretary
<PAGE>

STATE OF NEW YORK  )
                      :  SS.:
COUNTY OF ROCKLAND)


     On this 28 day of June, in the year two thousand and one, before me, the
             --
undersigned, personally appeared Dennis J. O'Connor, personally known to me or
proved to me on the basis of satisfactory evidence to be the individual whose
name is subscribed to the within instrument and acknowledged to me that he
executed same in his capacity and that by his signature on the instrument, the
individual, or the person upon behalf of which the individual acted, executed
the instrument and that such individual made such appearance before the
undersigned in the Town of Spring Valley, County of Rockland, State of New York.
                   ----    -------------            --------           --------



                                   /s/ Peter H. Streelman
                                   ----------------------------------
                                   (Signature and Office of
                                   individual taking acknowledgement)

STATE OF NEW YORK  )
                      )  ss.:
COUNTY OF  ROCKLAND   )

     On this 28 day of June, in the year two thousand and one, before me, the
             --
undersigned, personally appeared Peter H. Streelman personally known to me or
proved to me on the basis of satisfactory evidence to be the individual whose
name is subscribed to the within instrument and acknowledged to me that he
executed same in his capacity and that by his signature on the instrument, the
individual, or the person upon behalf of which the individual acted, executed
the instrument and that such individual made such appearance before the
undersigned in the Town of Spring Valley, County of Rockland, State of New York.
                   ----    -------------



                                   /s/ Kristen Hamilton
                                   ----------------------------------
                                   (Signature and Office of
                                   individual taking acknowledgement)
<PAGE>

STATE OF NEW YORK  )
                        :  SS.:
COUNTY OF ROCKLAND)


     On this 28 day of June, in the year two thousand and one, before me, the
             --
undersigned, personally appeared Dennis J. O'Connor, personally known to me or
proved to me on the basis of satisfactory evidence to be the individual whose
name is subscribed to the within instrument and acknowledged to me that he
executed same in his capacity and that by his signature on the instrument, the
individual, or the person upon behalf of which the individual acted, executed
the instrument and that such individual made such appearance before the
undersigned in the Town of Spring Valley, County of Rockland, State of New York.
                   ----    -------------            --------           --------




                                   /s/ Peter H. Streelman
                                   ----------------------------------
                                   (Signature and Office of
                                   individual taking acknowledgement)
<PAGE>

                          RESTATED MORTGAGE LOAN NOTE


$1,340,000.00                                            Dated as of May 1, 2001
                                                         Hawthorne, New Jersey


     The undersigned, PAR PHARMACEUTICAL, INC., with an address at One Ram Ridge
Road, Spring Valley, New York 10977, promises to pay to the order of Hudson
United Bank, successor in interest to Urban National Bank (the "Bank"), having
its principal office located at 1000 MacArthur Boulevard, Mahwah, New Jersey,
the principal sum of ONE MILLION THREE HUNDRED FORTY THOUSAND and NO/100
(1,340,000.00) DOLLARS as hereinafter provided or so much thereof as may be
outstanding, and to pay interest as hereinafter provided on the unpaid principal
balance of this Note from time to time, from the date hereof until the principal
balance is paid in full.

     1.   The unpaid principal balance shall earn interest (i) during the first
five (5) years of the term of this Note at the fixed rate of eight and one-half
(8-1/2) percent per annum; and (ii) during the next two (2) years of the term
hereof at a fixed rate of 8.5% percent per annum; (iii) during the next five (5)
years of the term of this Note at a fixed rate of interest equal to eight and
one-half (8-1/2) percent per annum; (iv) from May 1, 2006 through and including
April 30, 2011 at a fixed rate of interest equal to 325 basis points above the
interest rate charged by the Federal Home Loan Bank Board of New York on
mortgage loans having a maturity of five (5) years rounded up to the nearest
one-eighth of one (1/8) percent in effect forty-five (45) days before May 1,
2006; and (v) from May 1, 2011 until this Note is paid in full at a fixed rate
of interest equal to 325 basis points above the interest rate charged by the
Federal Home Loan Bank Board of New York on mortgage loans having a maturity of
five (5) years rounded up to the nearest one-eighth of one (1/8) percent in
effect forty-five (45) days before May 1, 2011.

     2.   All computations of interest shall be calculated on the basis of the
actual number of days elapsed divided by 360.

     3.   Payment of principal shall be made in eighty-three equal consecutive
monthly installments of $5,583.33, together with accrued and unpaid interest,
commencing on June 1, 1994 and continuing on the first day of each month
thereafter until May 1, 2001; and commencing on June 1, 2001 and continuing on
the same day of each and every month thereafter, the undersigned shall make a
periodic payment of principal and interest until May 1, 2014 (the "Maturity
Date") at which time the entire unpaid principal balance of this Note together
with all accrued but unpaid interest and all other amounts due under this Note
and the Mortgage shall be immediately due and payable. From June 1, 2001 through
May 1, 2006, the undersigned shall make a periodic payment and interest of
$9,366.05. The periodic payment of principal and interest shall be recalculated
on May 1, 2006 and May 1, 2011 based on the new interest rate then in effect,
the unpaid principal balance of this Note and the remaining term of this Note.

     4.   This Note which replaces and supersedes (but shall not be considered a
repayment of) a note of the undersigned dated May 4, 1994 in the original
principal amount of $1,340,000.00, (the "Prior Note"). Any and all amounts
evidenced by the Prior Note shall hereafter be evidenced by this Note and any
accrued but unpaid interest due and owing under the Prior Note shall be payable
on the first interest payment date hereunder.

     5.   If required by the Bank, on the first day of each month the
undersigned shall pay to the Bank one-twelfth (1/12th) of the sum of (a) the
taxes on the Mortgaged Premises (as defined below and (b) the aggregate premiums
for insurance coverage on the Mortgaged Premises payable within the succeeding
twelve months. The Bank shall hold such monies in an escrow account and apply
same to the payment of taxes and insurance premiums as same become payable.

     6.   As security for the payment of the money owing thereon, as well as the
performance of all items and conditions of this Note, the undersigned has
delivered to the Bank a first mortgage and security agreement of even date
herewith on real property located in the Town of Ramapo, Rockland County, New
York (the "Mortgage"). The real property encumbered by the Mortgage are
hereinafter referred to as the "Mortgaged Premises."  The terms, covenants and
conditions of the Mortgage are hereby made a part of this Note, to the extent
and with the same effect as if set forth herein at length and the undersigned
shall be bound and shall comply with all terms, covenants and conditions of the
Mortgage.
<PAGE>

     7.   The Bank may charge and the undersigned agrees to pay a penalty of
five (5) percent of any installment of interest and/or principal of any portion
thereof which is not paid within fifteen (15) days after the same become due and
payable under this Note.

     8.   Notwithstanding the foregoing, the unpaid balance of the principal
amount owing hereunder, together with interest thereon, shall immediately become
due and payable, at the election of the holder hereof, in the event of:

          (a)  A failure to make any payment of principal or interest hereunder
within ten (10) days after written notice of such non-payment form the Bank to
the undersigned;

          (b)  Failure to observe or perform any term, covenant or condition of
   this Note or the Mortgage (other than with respect to the payment of the
   principal or interest which shall be governed by (a) above) and, if no other
   grace period is applicable, within thirty (30) days after written notice of
   such default from the Ban to the undersigned and/or;

          (c)  Any event of default as defined in the Mortgage.

     9.   In the event of default, the Bank shall have the right immediately,
and without notice or other action, to set-off against the undersigned's
liability to the Bank any money owed by the Bank to the undersigned, whether due
or not, and the Bank shall be deemed to have exercised such right of set-off and
to have made a charge against any such money immediately upon the occurrence of
a default under this Note, even thought the actual book entries may be made at
some time subsequent thereto.

     10.  In addition to any late payment charge which may be due under this
Note, if the debt evidenced hereby is declared immediately due and payable by
the Bank pursuant to the provisions of this Note, or the Mortgage, or if the
debt evidenced hereby is not paid in full on the Maturity Date, the undersigned
shall hereafter pay interest on the principal balance form the date of such
declaration or the Maturity Date, as the case may be, until the date the
principal balance is paid in full, at the rate per annum (calculated for the
actual number of days elapsed on the basis of a 360-day year) equal to five (5)
percent per annum above the interest rate then in effect as set forth herein,
provided, however, that such interest rate shall in no event exceed the maximum
interest rate which the undersigned may by law pay (the "Default Rate").

     11.  This Note is subject to the express condition that at no time shall
the undersigned by obligated or required to pay interest on the principal
balance at the rate which could subject the Bank to either civil or criminal
liability as a result of being in excess of the maximum rate which the
undersigned is permitted by law to contract or agree to pay. If by the terms of
this Note, the undersigned is at any time required or obligated to pay interest
on the principal balance at a rate in excess of such maximum rate, the rate of
interest under this Note shall be deemed to be immediately reduced to such
maximum rate and interest payable hereunder shall be computed at such maximum
rate and interest payable hereunder shall be computed at such maximum rate and
the portion of al prior interest payments in excess of such maximum rate shall
be applied and shall be deemed to have been payments in reduction of the
principal balance.

     12.  Upon the continuance of any default in the payment of any installment
of interest and/or principal due hereunder, or of any portion thereof, or of any
penalty, or upon any default in the performance of any covenant, agreement or
conditions contained in the Mortgage within the time limits established in the
Mortgage, then at the option of the holder hereof, the whole principal sum with
accrued interest shall become and be immediately due and payable without further
notice, demand or presentment for payment.

     13.  Except as otherwise provided in this Note or the Mortgage, the
undersigned and all other parties who at any time may be liable hereon in any
capacity, jointly and severally, waive presentment, demand for payment, protest
and notice of dishonor of this Note, and authorize the Bank without notice, but
only with the consent of the undersigned, to grant extensions in the time of
payment of and reduction or increase in the rate of interest on any money owing
on this Note.

     14.  This Note may be prepaid, at any time, together with interest due to
the date of such prepayment, in increments of $25,000.00 without prepayment
penalty or additional premium.

     15.  The undersigned shall not enter into any additional financing with
respect to the Mortgaged Premises during the term of the loan evidenced by this
Note.
<PAGE>

     16.  The undersigned hereby waives its right to a jury trial.

     17.  This Note shall be construed according to and governed by the laws of
the State of New Jersey.

     18.  This Note may only be modified, amended, changed or terminated by an
agreement in writing signed by the Bank and the undersigned.  No waiver of any
term, covenant or provisions of the Note shall be effective unless given in
writing by the Bank and if so given by the Bank shall only be effective in the
specific instance in which given.

     19.  The undersigned expressly covenants and agrees that it will abide by
the terms and conditions of the commitment letter of the Bank to the undersigned
dated April 13, 1994, to the extent that such terms and conditions have not been
incorporated in this Note or the Mortgage.

     20.  No delay n the part of the Bank in exercising any right or remedy
under this Note or failure to exercise the same shall operate as a waiver in
whole or in part of any such right by or remedy.

     IN WITNESS WHEREOF, the undersigned has hereunto set its hand and seal or
caused these presents to be signed by its proper corporate officers and its
proper corporate seal to be hereto affixed the day and year first written above.

                                   PAR PHARMACEUTICAL, INC.



                                   by: /s/ Dennis J. O'Connor
                                      -------------------------------
                                      Dennis J. O'Connor
                                      Vice President, CFO and
                                      Secretary
<PAGE>

STATE OF NEW YORK  )
                         :  SS.:
COUNTY OF ROCKLAND)


     On this 28 day of June, in the year two thousand and one, before me, the
             --
undersigned, personally appeared Dennis J. O'Connor, personally known to me or
proved to me on the basis of satisfactory evidence to be the individual whose
name is subscribed to the within instrument and acknowledged to me that he
executed same in his capacity and that by his signature on the instrument, the
individual, or the person upon behalf of which the individual acted, executed
the instrument and that such individual made such appearance before the
undersigned in the Town of Spring Valley, County of Rockland, State of New York.
                   ----    -------------            --------           --------



                                   /s/ Peter H. Streelman
                                   ----------------------------------
                                   (Signature and Office of
                                   individual taking acknowledgement)