<PAGE>   1
                                                                   EXHIBIT 10.50

                            SECURED PROMISSORY NOTE



Amount:  $200,000                                            Detroit, Michigan
                                                             February 11, 1997


     FOR VALUE RECEIVED, Caraco Pharmaceutical Laboratories, Ltd., a Michigan
corporation ("Borrower"), promises to pay to the order of David A. Hagelstein,
as Trustee of the David Hagelstein Trust u/a/d October 27, 1993, the address of
which is 1411 N. Woodward, Suite 313, Birmingham, Michigan 48109 ("Lender"), or
at such other place as Lender may designate in writing, the principal sum of
Two Hundred Thousand and 00/100 ($200,000) Dollars, together with interest at
10.0% per annum payable in cash or shares of Common Stock of Borrower as
determined in the sole discretion of Borrower.  This Secured Promissory Note
(the "Note") shall mature, and all principal outstanding hereunder, together
with all accrued and unpaid interest thereon shall be due and payable on (A)
the earlier of (i) March 27, 1997, (ii) the closing of a transaction pursuant
to which Sun Pharmaceutical Industries Limited ("Sun Pharmaceutical") or an
affiliate acquires 5.3 million shares of the Common Stock of Borrower (the
"Proposed Transaction") or (iii) 20 days after delivery of a written notice by
Sun Pharmaceutical to Borrower that Lender does not intend to proceed with
and/or continue negotiations regarding the Proposed Transaction, unless such
failure to proceed constitutes a breach of any legal obligation which Sun
Pharmaceutical may hereafter incur in writing or (B) in any event, upon the
occurrence of a Default as defined pursuant to the Security Agreement (as
defined below).  In the event the outstanding principal and interest hereunder
are not paid when due, then until such principal balance or accrued interest is
paid, the outstanding principal balance and all accrued but unpaid interest
thereon shall bear interest at the rate 12% per annum.

     Notwithstanding any other provision of this Note or any other agreement
between Borrower and Lender, nothing herein shall require the Borrower to pay,
or the Lender to accept, interest in an amount which subjects the holder of
this Note to any penalty or forfeiture under applicable law, and in no event
shall the total of all charges payable hereunder (whether of interest or of
such other charges which may or might be characterized as interest) exceed the
maximum rate permitted to be charged under applicable law.  Should Lender or
any other holder of this Note receive any payment which is or would be in
excess of that permitted to be charged under applicable law, such payment shall
have been, and shall be deemed to have been made in error been made in error
and shall be held as additional cash collateral for the indebtedness evidenced
by this Note.



<PAGE>   2


     All payments on account of indebtedness evidenced by this Note shall be
made not later than 11:00 a.m. Detroit time on the date due hereunder in lawful
money of the United States without setoff or counterclaim whatsoever and
without reduction for, and free from, any and all present or future taxes,
levies, imposts, duties, fees, charges, deductions, withholdings, restrictions
or conditions of any nature imposed by any governmental body, and all payments
shall be first applied to any costs and expenses permitted hereunder, then
accrued and unpaid interest on the outstanding principal balance with the
remainder to be applied to any unpaid principal.

     This Note may be prepaid in whole or in part at any time and from time to
time without premium or penalty.  All payments shall be made in lawful money of
the United States of America.

     This Note is secured by a Security Agreement of even date herewith
("Security Agreement") and an Inter-Creditor Agreement dated January 30, 1997
("Inter-Creditor Agreement"), as each may be amended from time to time.
Reference is hereby made to the Security Agreement and the Inter-Creditor
Agreement with respect to the security given for this instrument.

     Borrower agrees to pay to Lender (or the holder of this Note) (a) all
costs and expenses incurred by the Lender or other holder hereof in collecting
hereon, whether through reorganization, bankruptcy, any other proceeding or
otherwise, (b) attorneys' and consultants fees and expenses in connection with
any proposed refinancing or restructuring of the credit provided in this Note
in the nature of a "work-out" and (c) all fees and expenses, including
attorneys fees, incurred in connection with the collection of this Note or the
enforcement of any of its rights under the Security Agreement or the
Inter-Creditor Agreement.

     Borrower, for itself, its successors, heirs and permitted assigns, and any
other parties now or hereafter liable for the payment hereof, expressly waives
presentment for payment, demand, notice of nonpayment, notice of protest and
protest of this Note, and diligence in collection, bringing suit or
acceleration.  The liability of Borrower to Lender shall be absolute and
unconditional, without regard to the liability of any other party.

     This Note and all rights of Lender hereunder shall inure to the benefit of
Lender's successors and assigns and shall bind Borrower and its successors and
permitted assigns.  Borrower shall be prohibited from assigning its obligations
hereunder or under the Security Agreement or under the Inter-Creditor Agreement
without the written consent of Lender.

     This Note shall be governed by and construed in accordance with the laws
of the State of Michigan.  If any provision of this Note is held by a court of
competent jurisdiction to be invalid, void or unenforceable, the remaining
provisions shall




<PAGE>   3


nonetheless continue in full force and effect without being impaired or
invalidated in any way.

     NEITHER LENDER NOR ANY OF ITS EMPLOYEES, AGENTS OR ATTORNEYS SHALL BE
LIABLE TO BORROWER FOR CONSEQUENTIAL OR SIMILAR DAMAGES ARISING FROM ANY BREACH
OF CONTRACT, TORT OR OTHER WRONG RELATING TO THIS NOTE OR ANY OTHER AGREEMENT
OR DOCUMENT RELATING HERETO.

     BORROWER HEREBY WAIVES TRIAL BY JURY IN ANY LITIGATION IN ANY COURT WITH
RESPECT TO, IN CONNECTION WITH, OR ARISING OUT OF THIS NOTE OR ANY INSTRUMENT
OR DOCUMENT DELIVERED PURSUANT HERETO.  THIS WAIVER IS INFORMED AND FREELY
MADE.

     IN WITNESS WHEREOF, the Borrower has caused this Note to be executed as of
the date and year executed below Borrower's signature.


WITNESSES                       CARACO PHARMACEUTICAL
                                LABORATORIES, LTD.,
                                a Michigan corporation

/s/Jennifer Evans               By:      /s/William R. Hurd
-----------------                        --------------------
                                         William R. Hurd
                                Its:     President

                                Date:    /s/February 12, 1997
                                         --------------------