Document:

<PAGE>

                                                                    Exhibit 10.7

                            FIRST AMENDMENT TO THE
                              SECURITY AGREEMENT

     THIS FIRST AMENDMENT TO THE SECURITY AGREEMENT, dated as of June 20, 2001
(this "Amendment"), by and between SENETEK, plc, a corporation organized under
       ---------
the laws of England (the "Company") and each of the undersigned (each a
                          -------
"Guarantor", and collectively with the Company, the "Grantors") and SILVER CREEK
----------                                           --------
INVESTMENTS, LTD., a British Virgin Islands company, as Collateral Agent for the
benefit of the purchasers (the "Original Purchasers") set forth on Schedule 1 of
                                -------------------                ----------
the Original Purchase Agreement (as defined below) and the Lender (as defined
below) (the "Collateral Agent").
             ----------------

     WHEREAS, the Company and the Original Purchasers have entered into a
Securities Purchase Agreement dated as of April 14, 1999 (the "Original Purchase
                                                               -----------------
Agreement");
---------

     WHEREAS, as collateral security for payment and performance of its Secured
Obligations (as defined in the Security Agreement), the Company and the
Guarantors each granted to the Collateral Agent for the benefit of the Original
Purchasers a security interest in certain of its personal property and assets
pursuant to the terms of the Security Agreement by and between the Company, the
Guarantors and the Collateral Agent, dated as of April 14, 1999 (as the same
from time to time may be amended, modified, supplemented, extended or restated,
the "Security Agreement");
     ------------------

     WHEREAS, Wallington Investments Limited, a corporation organized under the
laws of the British Virgin Islands (the "Lender"), has agreed to extend certain
                                         ------
financial accommodations to the Company in connection with the financing of the
working capital needs of the Company, and Wallington is willing to extend such
financial accommodations to the Company pursuant to the terms of a Revolving
Credit Agreement to be entered into by the Company and Lender (the "Credit
                                                                    ------
Agreement");
---------

     WHEREAS, as a condition to Lender entering into the Credit Agreement and
extending financial accommodations to the Company thereunder, and in
consideration thereof, the Company and the Original Purchasers are (i) entering
into a First Amendment to the Purchase Agreement dated the date hereof (the
"First Amendment"; the Original Purchase Agreement, as amended by the First
 ---------------
Amendment is referred to herein as the "Purchase Agreement") in order to modify
                                        ------------------
certain terms of the Original Purchase Agreement to, among other things, permit
the Company to enter into the Credit Agreement and (ii) amending certain of the
Transaction Documents, including, without limitation, the Security Agreement, to
include the Lender as a secured party thereunder. Capitalized terms used but not
otherwise defined herein shall have the meaning set forth in the Purchase
Agreement;

     WHEREAS, the Lender is unwilling to enter into the Credit Agreement unless
the Company and the Collateral Agent on behalf of the Original Purchasers and
the Lender enter into this Amendment;
<PAGE>

     NOW, THEREFORE, in consideration of the mutual promises hereinafter set
forth and for other good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties hereto, intending to be legally
bound hereby, do hereby agree as follows:

     1.   Amendments to the Security Agreement. (a)  The heading of the Security
          ------------------------------------
Agreement shall be amended and restated to read as follows:

          "THIS SECURITY AGREEMENT, dated as of April 14, 1999, as amended by
     the First Amendment dated June 20, 2001 (this "Agreement"), is made by and
     between SENETEK, plc, a corporation organized under the laws of England
     (the "Company") and each of the undersigned (each a "Guarantor", and
           -------                                        ---------
     collectively with the Company, the "Grantors") and SILVER CREEK
                                         --------
     INVESTMENTS, LTD., a British Virgin Islands company, as Collateral Agent
     (the "Collateral Agent") for the benefit of the purchasers (the "Original
           ----------------
     Purchasers") set forth on Schedule 1 of the Purchase Agreement (as defined
                               ----------
     below) and Wallington Investments Limited, a company organized under the
     laws of the British Virgin Islands (the "Lender").  All capitalized terms
                                              ------
     used but not otherwise defined herein shall have the respective meanings
     assigned thereto in the Purchase Agreement (as defined below) except that
     (i) the term "Purchasers" as used herein shall in all cases be deemed to
     include both the Purchasers and the Lender and (ii) the term "Event of
                                                                   --------
     Default" as used herein shall in all cases be deemed to include both an
     -------
     Event of Default (as defined in the Purchase Agreement) and (ii) an Event
     of Default (as defined in the Credit Agreement)."

          (b) The first paragraph of Section 1 (Grant of Security Interest) of
                                                --------------------------
the Security Agreement is hereby amended and restated as follows:

          "As collateral security for the payment, performance, and satisfaction
     of (i) all the Guarantors' Obligations (as defined in the Guaranty), (ii)
     all of the Company's Obligations (as defined in the Purchase Agreement) and
     (iii) all of the Company's Obligations (as defined under the Credit
     Agreement; (i), (ii) and (iii) collectively, the "Secured Obligations"),
                                                       -------------------
     each Grantor hereby affirms, grants, pledges and assigns to the Collateral
     Agent for the benefit of the Purchasers and grants to the Collateral Agent
     for the benefit of the Purchasers a continuing FIRST priority security
     interest in and to all of the property of such Grantor, subject to
     Permitted Liens, whether now owned or existing or hereafter acquired or
     arising and wheresoever located, including without limitation the
     following:"

     2.  Conditions to Effectiveness.  This Amendment shall become effective
         ---------------------------
only upon the satisfaction or waiver of all of the following conditions
precedent:

     (a)  The parties hereto shall have duly executed and delivered this
Amendment.

                                       2
<PAGE>

     (b)  The Borrower shall have satisfied all conditions to effectiveness
under Section 6 of the First Amendment.

     (c)  The Borrower shall have paid all fees and expenses required to be paid
by it pursuant to Section 5 of the First Amendment.

     3.   Representations and Warranties.  In order to induce the Collateral
          ------------------------------
Agent to enter into this Amendment (on behalf of the Original Purchasers and the
Lender), the Company hereby represents and warrants to the Original Purchasers
and the Lender that the Company has full power, right and legal authority to
execute, deliver and perform its obligations under this Amendment.  The Company
has taken all corporate action necessary to authorize the execution and delivery
of, and the performance of its obligations under, this Amendment.  This
Amendment constitutes a legal, valid and binding obligation of the Company
enforceable against it in accordance with its terms, subject to the effect of
any applicable bankruptcy, insolvency, reorganization or moratorium or similar
laws affecting the rights of creditors generally. The Company hereby ratifies
and reaffirms each of the Security Agreement (as amended hereby) and the other
related documents and all of the Company's covenants, duties and liabilities
thereunder.

     4.   Amendments. This Amendment may not be amended, modified or
          ----------
supplemented except by a subsequent written agreement signed by the parties
hereto.

     5.   Counterparts. This Amendment may be executed simultaneously in any
          ------------
number of counterparts.  Each counterpart shall be deemed to be an original, and
all such counterparts shall constitute one in the same instrument.

     6.   Governing Law.  This Amendment shall be governed by the laws of the
          -------------
State of New York (without giving effect to any conflicts of law rules or
principles).

     7.   Headings.   The headings of this Amendment are included herein for
          --------
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

     8.   Survival of the Security Agreement.  Each reference in the Security
          ----------------------------------
Agreement to "this Agreement," "hereunder," "hereof," "herein" or words of like
import, and each reference to the Security Agreement in any related document
(other than the Security Agreement) shall mean and be a reference to the
Security Agreement as amended hereby. Except as specifically amended by this
Amendment, the Security Agreement shall remain in full force and effect and is
hereby ratified, confirmed and acknowledged by the Company. This Amendment shall
not be deemed to (i) be a consent to any waiver or modification of any term or
condition of the Security Agreement or any document delivered pursuant thereto,
except in each case as expressly provided herein, or (ii) prejudice any right or
rights the Original Purchasers or the Lender may now or in the future have in
connection with the Security Agreement.

      [Signature page follows, remainder of page is intentionally blank]

                                       3
<PAGE>

          IN WITNESS WHEREOF, the parties have duly executed this First
Amendment to the Security Agreement the day and year first written above.

                              GRANTORS:
                              --------

                              SENETEK PLC

                              By: /s/ Frank J. Massino
                                  --------------------
                              Name:  Frank J. Massino
                              Title: President

                              SENETEK DRUG DELIVERY
                              TECHNOLOGIES, INC.

                               By: /s/ Frank J. Massino
                                   --------------------
                               Name:  Frank J. Massino
                               Title: President

                              CARME COSMECEUTICAL
                              SCIENCES, INC.

                              By: /s/ Frank J. Massino
                                  --------------------
                              Name:  Frank J. Massino
                              Title: President

                              SECURED PARTY:
                              -------------

                              SILVER CREEK INVESTMENTS, LTD.
                              as Collateral Agent for the benefit of the
                              Original Purchasers and the Lender

                              By: /s/ Robert T. Tucker
                                  --------------------
                              Name:  Robert T. Tucker
                              Title: Director

           [Signature page to First Amendment to Security Agreement]

                                       4<PAGE>

                                                                    Exhibit 10.8
                            FIRST AMENDMENT TO THE
                               PLEDGE AGREEMENT

     THIS FIRST AMENDMENT TO THE PLEDGE AGREEMENT, dated as of June 20, 2001
(this "Amendment"), by and between SENETEK PLC, a corporation organized under
the laws of England (the "Pledgor"), and SILVER CREEK INVESTMENTS, LTD., a
                          -------
British Virgin Islands company (the "Secured Party"), in its capacity as
                                     -------------
Collateral Agent under that certain Collateral Agency Agreement dated as of
April 14, 1999 as amended by the First Amendment dated the date hereof by and
among the Secured Party, Bomoseen Investments, Ltd., a British Virgin Islands
company ("Bomoseen"), Dandelion Investments, Ltd., a British Virgin Islands
          --------
company ("Dandelion"), and Elstree Holdings, Ltd., a British Virgin Islands
          ---------
company ("Elstree" and together with the Secured Party, Bomoseen and Dandelion,
          -------
the "Original Purchasers") and Wallington Investments Limited, a corporation
     -------------------
organized under the laws of the British Virgin Islands (the "Lender").
                                                             ------

     WHEREAS, the Company and the Original Purchasers have entered into a
Securities Purchase Agreement dated as of April 14, 1999 (the "Original Purchase
                                                               -----------------
Agreement");
---------

     WHEREAS, pursuant to the terms of the Pledge Agreement dated as of April
14, 1999 (the "Pledge Agreement") by and between the Pledgor and the Secured
               ----------------
Party (on behalf of the Original Purchasers), as collateral security for the
payment and performance of the Secured Obligations (as defined therein), the
Pledgor pledged and granted to the Secured Party for the ratable benefit of the
Original Purchasers a security interest the Pledged Stock (as defined in the
Pledge Agreement) including without limitation the Pledged Subsidiaries (as
defined in the Pledge Agreement); and

     WHEREAS, the Lender has agreed to extend certain financial accommodations
to the Pledgor in connection with the financing of the working capital needs of
the Pledgor, and Lender is willing to extend such financial accommodations to
the Pledgor pursuant to the terms of a Revolving Credit Agreement to be entered
into by the Pledgor and the Lender (the "Credit Agreement");
                                         ----------------

     WHEREAS, as a condition to Lender entering into the Credit Agreement and
extending financial accommodations to the Pledgor thereunder, and in
consideration thereof, the Pledgor and the Original Purchasers are (i) entering
into a First Amendment to the Purchase Agreement dated the date hereof (the
"First Amendment"; the Original Purchase Agreement, as amended by the First
----------------
Amendment is referred to herein as the "Purchase Agreement") in order to modify
                                        ------------------
certain terms of the Original Purchase Agreement to, among other things, permit
the Pledgor to enter into the Credit Agreement and (ii) amending certain of the
Transaction Documents, including, without limitation, the Pledge Agreement, to
include the Lender as a secured party thereunder. Capitalized terms used but not
otherwise defined herein shall have the meaning set forth in the Purchase
Agreement;
<PAGE>

     WHEREAS, the Lender is unwilling to enter into the Credit Agreement unless
the Pledgor and the Secured Party on behalf of the Original Purchasers and the
Lender enter into this Amendment;

     NOW, THEREFORE, in consideration of the mutual promises hereinafter set
forth and for other good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties hereto, intending to be legally
bound hereby, do hereby agree as follows:

     1.   Amendments to the Pledge Agreement. (a)  The heading of the Pledge
          ----------------------------------
Agreement shall be amended and restated to read as follows:

          "THIS PLEDGE AGREEMENT, dated as of April 14, 1999, as amended by the
     First Amendment dated June 20, 2001 (this "Agreement"), is made by and
     between SENETEK PLC, a corporation organized under the laws of England (the
     "Pledgor"), and Silver Creek Investments, Ltd., a British Virgin Islands
      -------
     company (the "Secured Party"), in its capacity as Collateral Agent under
                   -------------
     that certain Collateral Agency Agreement dated as of April 14, 1999 as
     amended by the First Amendment dated as of June 20, 2001 by and among the
     Secured Party, Bomoseen Investments, Ltd., a British Virgin Islands company
     ("Bomoseen"), Dandelion Investments, Ltd., a British Virgin Islands company
     ("Dandelion"), and Elstree Holdings, Ltd., a British Virgin Islands company
     ("Elstree" and together with the Secured Party, Bomoseen and Dandelion, the
     "Original Purchasers") and Wallington Investments Limited, a corporation
     organized under the laws of the British Virgin Islands (the "Lender"). All
     capitalized terms used but not otherwise defined herein shall have the
     respective meanings assigned thereto in the Purchase Agreement (as defined
     below) except that (i) the term "Purchasers" as used herein shall in all
     cases be deemed to include both the Original Purchasers and the Lender and
     (ii) the term "Event of Default" as used herein shall in all cases be
     deemed to include both an Event of Default (as defined in the Purchase
     Agreement) and (ii) an Event of Default (as defined in the Credit
     Agreement)."

          (b)  The first paragraph of Section 1 (Pledge of Stock; Other
                                                ----------------------
Collateral) of the Pledge Agreement is hereby amended and restated as follows:
----------

          "As collateral security for the payment, performance, and satisfaction
     of (i) all of the "Obligations" (as defined in the Purchase Agreement) and
     (ii) all of the "Obligations" (as defined under the Credit Agreement; (i)
     and (ii) collectively, the "Secured Obligations"), the Pledgor hereby
                                 -------------------
     pledges and collaterally assigns to the Secured Party, and grants to the
     Secured Party a FIRST priority lien and security interest in, the Pledged
     Stock and all of the following, subject only to Permitted Liens:"

                                       2
<PAGE>

     2.  Conditions to Effectiveness.  This Amendment shall become effective
         ---------------------------
only upon the satisfaction or waiver of all of the following conditions
precedent:

     (a) The parties hereto shall have duly executed and delivered this
Amendment.

     (b) The Pledgor shall have satisfied all conditions to effectiveness under
Section 6 of the First Amendment.

     (c) The Pledgor shall have paid all fees and expenses required to be paid
by it pursuant to Section 5 of the First Amendment.

     3.     Representations and Warranties. In order to induce the Secured Party
            ------------------------------
to enter into this Amendment (on behalf of the Original Purchasers and the
Lender), the Pledgor hereby represents and warrants to the Original Purchasers
and the Lender that the Pledgor has full power, right and legal authority to
execute, deliver and perform its obligations under this Amendment. The Pledgor
has taken all corporate action necessary to authorize the execution and delivery
of, and the performance of its obligations under, this Amendment. This Amendment
constitutes a legal, valid and binding obligation of the Pledgor enforceable
against it in accordance with its terms, subject to the effect of any applicable
bankruptcy, insolvency, reorganization or moratorium or similar laws affecting
the rights of creditors generally. The Pledgor hereby ratifies and reaffirms
each of the Pledge Agreement (as amended hereby) and the other related documents
and all of the Pledgor's covenants, duties and liabilities thereunder.

     4.     Amendments. This Amendment may not be amended, modified or
            ----------
supplemented except by a subsequent written agreement signed by the parties
hereto.

     5.     Counterparts. This Amendment may be executed simultaneously in any
            ------------
number of counterparts.  Each counterpart shall be deemed to be an original, and
all such counterparts shall constitute one in the same instrument.

     6.     Governing Law.  This Amendment shall be governed by the laws of the
            -------------
State of New York (without giving effect to any conflicts of law rules or
principles).

     7.     Headings.   The headings of this Amendment are included herein for
            --------
convenience of reference only and shall not constitute a part of this Amendment
for any other purpose.

     8.     Survival of the Pledge Agreement. Each reference in the Pledge
            --------------------------------
Agreement to "this Agreement," "hereunder," "hereof," "herein" or words of like
import, and each reference to the Pledge Agreement in any related document
(other than the Pledge Agreement) shall mean and be a reference to the Pledge
Agreement as amended hereby. Except as specifically amended by this Amendment,
the Pledge Agreement shall remain in full force and effect and is hereby
ratified, confirmed and acknowledged by the Pledgor. This Amendment shall not be
deemed to (i) be a consent to any waiver or modification of any term or
condition of the Pledge Agreement or any document delivered pursuant thereto,
except in each case as expressly provided herein, or (ii)

                                       3
<PAGE>

prejudice any right or rights the Original Purchasers or the Lender may now or
in the future have in connection with the Pledge Agreement.

[The remainder of this page intentionally left blank.  Signature page follows.]

                                       4
<PAGE>

     IN WITNESS WHEREOF, the parties have duly executed this First Amendment to
the Pledge Agreement on the day and year first written above.

                              PLEDGOR:
                              -------

                              SENETEK PLC, as the Pledgor

                              By: /s/ Frank J. Massino
                                  --------------------
                              Name: Frank J. Massino
                              Title: President

                              SECURED PARTY:
                              -------------

                              SILVER CREEK INVESTMENTS, LTD.,
                              as Collateral Agent for the Original Purchasers
                              and the Lender

                              By: /s/ Robert T. Tucker
                                  --------------------
                              Name: Robert T. Tucker
                              Title: Director

          [Signature page to First Amendment to the Pledge Agreement]

                                       5

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