Document:

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                                                                   Exhibit 10.90

                                 BIOSHIELD (TM)

                          BIOSHIELD TECHNOLOGIES, INC.

                                  June 27, 2000

Jackson, LLC
Wilson, LLC
c/o Citco Trustees (Cayman) Ltd.
Attn: David Sims
Corporate Center, Windwood One
West Bay Road
P.O. Box 31106 SMB
Grand Cayman, Cayman Islands

         RE: BIOSHIELD TECHNOLOGIES, INC. (THE "COMPANY")

Dear Mr. Sims:

         In consideration of and as a condition to the closing of the private
placement by the parties of the Company's $10,000,000 Series B Convertible
Preferred Stock and $50,000,000 Private Equity Credit Agreement (the "2000
Equity Line") of even date herewith, the parties hereto as holders of (i) Series
A Convertible Preferred Stock; (ii) Series B Convertible Preferred Stock; (iii)
common stock, no par value, of the Company ("Common Stock") issuable pursuant to
that certain Private Equity Credit Agreement, dated as of June 1999 and the 2000
Equity Line; (iv) Electronic Medical Distribution, Inc. common stock, par value
$0.0001 per share, which is exchangeable into Common Stock; and (v) Common Stock
issued as a result of (i)-(iv) above ((i)-(v) shall be collectively referred to
as Common Stock Holders") hereby agree as follows:

         1.       Limitation on Sales of Common Stock. The Common Stock Holders
                  and their affiliates agree not to directly or indirectly at
                  any time sell more than 20,000 shares of Common Stock on any
                  Trading Day; provided, however, (i) that if the daily volume
                  of the Common Stock, as reported by Bloomberg on any Trading
                  Day is greater than 100,000 per day and less than 250,000
                  (excluding any Common Stock sold by the Common Stock Holders),
                  then the Common Stock Holders may be permitted to sell a total
                  of 40,000 shares of Common Stock on any such Trading Day; (ii)
                  that if the daily volume of the Common Stock, as reported by
                  Bloomberg on any Trading Day is greater than 250,000 and less
                  than 500,000 shares of Common Stock (excluding any Common
                  Stock sold by the

                5655 Peachtree Parkway, Norcross, Georgia 30092;
                    Tel: (770) 246-2000; Fax: (770) 368-0784
<PAGE>   2
                  Common Stock Holders) then the Common Stock Holders may be
                  permitted to sell a total of 70,000 shares of Common Stock on
                  any such Trading Day; (iii) no sales may be made within the
                  last hour of each Trading Day. Notwithstanding the foregoing
                  limitation on such sales, the holder shall be permitted to
                  sell on any Trading Day without any limitation on such sales
                  in the event that the daily trading volume (excluding any
                  Common Stock sold by the Common Stock Holders) is in excess of
                  500,000 shares on any Trading Day (preceding any Common Stock
                  held by the Common Stock Holder).

         2.       Binding Nature of Agreement. The terms of this letter are
                  intended to be binding on any transferee or assignee of the
                  Common Stock Holders and no such transfer or assignment shall
                  be effective until such transferee or assignee agrees in
                  writing to be bond by the terms of this letter.

         3.       Definitions. Terms not otherwise defined herein shall have the
                  meaning set forth in the Articles of Amendment of the Company
                  dated as of June 14, 2000.

         4.       Counterparts. This agreement may be executed in counterparts,
                  which together shall constitute a single instrument.

                                      BIOSHIELD TECHNOLOGIES, INC.

                                      By: _____________________________
                                      Name:
                                      Title:

Accepted and agreed to this 15 day of June, 2000.

JACKSON, LLC

HOLDER OF ELECTRONIC MEDICAL DISTRIBUTION, INC. COMMON STOCK

By: _______________________________________
Name:
Title:

                5655 Peachtree Parkway, Norcross, Georgia 30092;
                    Tel: (770) 246-2000; Fax: (770) 368-0784
<PAGE>   3
JACKSON LLC

BUYER OF COMMON STOCK OF BIOSHIELD TECHNOLOGIES, INC. JUNE 1999 PRIVATE EQUITY
LINE AND HOLDER OF COMMON STOCK

By: _______________________________________
Name:
Title:

WILSON LLC

HOLDER OF BIOSHIELD TECHNOLOGIES, INC. SERIES A PREFERRED STOCK

By: _______________________________________
Name:
Title:

                5655 PEACHTREE PARKWAY, NORCROSS, GEORGIA 30092;
                    TEL: (770) 246-2000; Fax: (770) 368-0784<PAGE>   1
                                                                   Exhibit 10.91

                              OFFICER'S CERTIFICATE

         The undersigned, Timothy C. Moses, hereby certifies that he is the
President and Chief Executive Officer of BioShield Technologies, Inc., a Georgia
corporation (the "COMPANY") and that, as such, he is authorized to execute, this
Officer's Certificate on behalf of the Company and with reference to that
certain Securities Purchase Agreement dated as of June 14, 2000, (the
"AGREEMENT")

         1. The representations and warranties made by the Company in Section 3
of the Agreement are true and correct as of the date of this Certificate. The
capitalization of the Company disclosed on Schedule 3(c) of the Agreement has
not changed.

         2. All of the Company's obligations specified in the Agreement to be
satisfied at or prior to a Closing thereunder have been satisfied or performed.

         3. There have been no adverse change in the business, affairs,
prospects, operations, properties, assets or condition of a Company since June
30, 1999, the date of the Company's most recent audited financial statements.

         IN WITNESS WHEREOF, the undersigned has executed this certificate on
June 14, 2000.

                                  BIOSHIELD TECHNOLOGIES, INC.

                                  By:______________________________________
                                  Name:    Timothy C. Moses
                                  Title:   President and Chief Executive Officer<PAGE>   1
                                                                   Exhibit 10.92

                           TRANSFER AGENT INSTRUCTIONS

                          BIOSHIELD TECHNOLOGIES, INC.

                                 June 14, 2000

American Stock Transfer
40 Wall Street
New York, New York  10005

ATTN: WILBERT MYLES

Dear Mr. Myles:

         Reference is made to that certain Securities Purchase Agreement, of
even date herewith, by and among BioShield Technologies, Inc., a Georgia
corporation (the "COMPANY"), and each of the subscribers listed in Exhibit "A"
attached hereto (collectively, the "HOLDERS") pursuant to which the Company is
issuing to the Holders an aggregate of 200 shares of Series B Preferred Stock,
no par value, of the Company (the "PREFERRED SHARES"). This letter shall serve
as our irrevocable authorization and direction to you (provided that you are the
transfer agent of the Company at such time) to issue shares (the "CONVERSION
SHARES") of Common Stock, no par value (the "COMMON STOCK"), of the Company to
or upon the order of a Holder from time to time upon (i) surrender to you of a
properly completed and duly executed Conversion Notice, in the form attached
hereto as Exhibit I, which has been properly agreed and acknowledged by the
Company as indicated by the signature of a duly authorized officer of the
Company thereon and (ii) certificates representing Preferred Shares being
converted (or an indemnification undertaking with respect to such shares in the
case of their loss, theft or destruction). So long as you have previously
received: (i) written confirmation from counsel to the Company that a
registration statement covering resales of the Conversion Shares has been
declared effective by the U.S. Securities and Exchange Commission (the "SEC")
under the Securities Act of 1933, as amended (the "1933 ACT"), and (ii) a copy
of such Registration Statement, Certificates representing the Conversion Shares
shall not bear any legend restricting transfer of the Conversion Shares thereby
and should not be subject to any stop-transfer restriction. However, if you have
not previously received (i) written confirmation from counsel to the Company
that a registration statement covering resales of the Conversion Shares has been
declared effective by the Securities and Exchange Commission under the
Securities Act of 1933, as amended, and (ii) a copy of such registration
statement, then the certificates representing the Conversion Shares shall bear
the following legend:

         "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
         REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE
         STATE SECURITIES LAWS. THE SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT
         AND MAY NOT BE OFFERED FOR SALE, SOLD, TRANSFERRED OR ASSIGNED IN THE
         ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER
         THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE
<PAGE>   2
         SECURITIES LAWS, OR AN OPINION OF COUNSEL, IN A REASONABLY ACCEPTABLE
         FORM, THAT REGISTRATION IS NOT REQUIRED UNDER SAID ACT OR APPLICABLE
         STATE SECURITIES LAWS OR UNLESS SOLD PURSUANT TO RULE 144 UNDER SAID
         ACT."

provided, however, that the Company may from time to time notify you to place
stop transfer restrictions on the certificates for the Conversion Shares in the
event a registration statement covering the Conversion Shares is subject to
amendment for events then current.

         An opinion of counsel to the Company that the issuance of the
Conversion Shares to the Holders will be exempt from registration under the 1933
Act is attached hereto as Exhibit II.

         Please be advised that the Holders are relying upon this letter as an
inducement to enter into the Securities Purchase Agreement and, accordingly,
each Holder is a third party beneficiary to these instructions.

         Should you have any questions concerning this matter please contact me
at (770) 326-9890.

                                       Very truly yours,

                                       BIOSHIELD TECHNOLOGIES, INC.

                                       By:_____________________________________
                                       Name:

                                       Its:

ACKNOWLEDGED AND AGREED:

TRANSFER AGENT

By:______________________________________
Name: ___________________________________
Title: ____________________________________
Date: ____________________________________

Enclosure

cc: Holders
<PAGE>   3
                                   EXHIBIT "A"

                               SCHEDULE OF BUYERS

--------------------------------------------------------------------------------

                                                               NUMBER OF SERIES
                                                               B PREFERRED
BUYER'S NAME           ADDRESS/FACSIMILE NUMBER OF BUYER       SHARES

--------------------------------------------------------------------------------

WILSON LLC             c/o Citco Trustees (Cayman) Ltd.        500
                       Attn: David Sims
                       Corporate Centre, Windwood One
                       West Bay Road
                       P.O. Box 31106 SMB
                       Grand Cayman, Cayman Islands
                       284-494-4771
--------------------------------------------------------------------------------
<PAGE>   4
                                    EXHIBIT I

                          BIOSHIELD TECHNOLOGIES, INC.

                                CONVERSION NOTICE

         Reference is made to the Amendments to the Articles of Incorporation of
BioShield Technologies, Inc.. (the "AMENDMENT"). In accordance with and pursuant
to the Amendment, the undersigned hereby elects to convert the number of shares
of Series B Convertible Preferred Stock, no par value per share (the "SERIES B
PREFERRED SHARES"), of BioShield Technologies, Inc., a Georgia corporation (the
"COMPANY"), indicated below into shares of Common Stock, no par value per share
(the "COMMON STOCK"), of the Company, by tendering the stock certificate(s)
representing the share(s) of Series B Preferred Shares specified below as of the
date specified below.

         The undersigned acknowledges that any sales by the undersigned of the
securities issuable to the undersigned upon conversion of the Series B Preferred
Shares shall be made only pursuant to (i) a registration statement effective
under the Securities Act of 1933, as amended (the "ACT"), or (ii) advice of
counsel that such sale is exempt from registration required by Section 5 of the
Act.

                                             Date of Conversion:

                                             -----------------------------------

                                             Number of Series B
                                             Preferred Shares to be converted

                                             -----------------------------------

                                             Stock certificate no(s). of Series
                                             B Preferred Shares to be converted:

                                             -----------------------------------

Please confirm the following information:

                                             Conversion Price:

                                             -----------------------------------

                                             Ten Days Comprising Pricing Period
                                             and Three Lowest Prices:

                                             -----------------------------------

                                             Number of shares of Common
                                             Stock to be issued:

                                             -----------------------------------
<PAGE>   5
please issue the Common Stock into which the Series B Preferred Shares are being
converted in the following name and to the following address:

                                   Issue to:(1)

                                   ---------------------------------------------

                                   ---------------------------------------------
                                   Facsimile Number:

                                   ---------------------------------------------

                                   Authorization:

                                   ---------------------------------------------
                                   By:
                                      ------------------------------------------

                                   Title:
                                         ---------------------------------------
                                   Dated:
                                         ---------------------------------------

ACKNOWLEDGED AND AGREED:

BIOSHIELD TECHNOLOGIES, INC.

By:
   ----------------------------------
Name:
     --------------------------------
Title:
      -------------------------------
Date:
      -------------------------------

---------------
         (1)If other than to the record holder of the Series B Preferred Shares,
any applicable transfer tax must be paid by the undersigned.
<PAGE>   6
                                   EXHIBIT II

                          BIOSHIELD TECHNOLOGIES, INC.

Attached hereto.

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