<PAGE>   1
                                                                    EXHIBIT 10-B

                                    AMENDMENT
                                       TO
                     PRIVATE EQUITY LINE OF CREDIT AGREEMENT

         AMENDMENT TO PRIVATE EQUITY LINE OF CREDIT AGREEMENT, dated as of
______________, 1997 ("Amendment"), among DEERE PARK CAPITAL MANAGEMENT, an
Illinois limited liability company (the "Investor Agent"), BARTHOLOMEW
INVESTMENT, L.P., an Illinois limited partnership (together with the Investor
Agent, the "Investors"), and ZILA, INC., a Delaware corporation (the "Company").

                                R E C I T A L S:

         A.       The parties have heretofore entered into that certain Private
Equity Line of Credit Agreement dated as of April 30, 1997 (the "Credit
Agreement").

         B.       The parties desire to amend the Credit Agreement for the
purpose of clarification, as set forth herein.

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

         1.       AMENDMENTS. The Credit Agreement is hereby amended as follows:

                  (a)      SECTION 1.4 is hereby amended in its entirety to read
         as follows:

                           Section 1.4 "Closing Date" shall mean, with respect
                  to each purchase and sale of Common Stock pursuant to this
                  Agreement, (i) with respect to the Initial Shares, the fifth
                  Trading Day following the Subscription Date, and (ii) with
                  respect to Option Shares, an Optional Purchase Date, provided
                  in each case that all conditions to the applicable Closing
                  have been satisfied.


                                        1


<PAGE>   2


                  (b)      SECTION 1.15 is hereby amended in its entirety to
         read as follows:

                           Section 1.15 "Market Price" shall mean (i) with
                  respect to sale of the Initial Shares, the closing bid price
                  (as reported by Bloomberg, L.P.) of the Company's Common Stock
                  on the Trading Day immediately preceding the Subscription Date
                  and (ii) with respect to Repricing Events and sale of Optional
                  Shares, the average of the closing bid price (as reported by
                  Bloomberg, L.P.) of the Company's Common Stock over the
                  10-Trading Day period commencing on the First Effective Date,
                  the Second Effective Date, and the applicable Optional
                  Purchase Date.

                  (c)      SECTION 1.17 is hereby amended in its entirety to
         read as follows:

                           Section 1.17 "Optional Purchase Date" shall mean,
                  during the Commitment Period, the third Trading Day following
                  delivery to the Investor Agent of an Optional Purchase Notice
                  pursuant to Section 2.6 on which the Company elects to sell
                  Common Stock to the Investors, in conformity with the
                  provisions of this Agreement.

                  (d)      SECTION 2.5(d) is hereby amended by deleting the
         second sentence thereof and inserting in lieu thereof the following:

                           Delivery of certificates to escrow shall occur (i)
                  three (3) business days following the Subscription Date, the
                  First or Second Effective Date, as applicable, or (ii)
                  concurrently with the delivery of an Optional Purchase Notice
                  pursuant to Section 2.5(c).

         2.       RATIFICATION. Except as otherwise amended herein, the parties
hereby ratify and affirm the Credit Agreement in all respects.

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


                                        2


<PAGE>   3


DEERE PARK CAPITAL MANAGEMENT                   ZILA, INC.


By:___________________________                  By:____________________________
Its:_____________________________               Its:____________________________

BARTHOLOMEW INVESTMENT, L.P.


By:______________________________
Its:______________________________


                                        3