Document:

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                                                                   Exhibit 10.11
                            FIRST AMENDMENT TO THE
                    PATENT AND TRADEMARK SECURITY AGREEMENT

     THIS FIRST AMENDMENT TO THE PATENT AND TRADEMARK 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 "Grantor", 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 Original
                 -------------------                ----------
Purchase Agreement (as defined below) and the Lender (as defined below).

     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
Obligations (as defined in the Original Purchase Agreement), each of the
Grantors granted to the Original Purchasers a security interest in all of its
patents and trademarks pursuant to the terms of the Patent and Trademark
Security Agreement by and among the Grantors and the Collateral Agent (as the
same from time to time may be amended, modified, supplemented, extended or
restated, the "Patent and Trademark 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 Lender 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 Patent and Trademark
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;
<PAGE>

     WHEREAS, the Lender is unwilling to enter into the Credit Agreement unless
the Grantors and the Collateral Agent 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 Patent and Trademark Security Agreement. (a) The
          ---------------------------------------------------------
heading of the Patent and Trademark Security Agreement shall be amended and
restated to read as follows:

          "THIS PATENT AND TRADEMARK 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 "Grantor", 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").
                                                        ------

          (b)  The fourth "WHEREAS" clause of the Patent and Trademark Security
Agreement is hereby amended and restated in its entirety as follows:

          "WHEREAS, as collateral security for payment and performance of: (i)
     the Company's Obligations under the Purchase Agreement, the Credit
     Agreement, the Lender's Note and any and all related documents; and (ii)
     the Guarantors' Obligations (as defined in the Guaranty (as such Guaranty
     is amended by the First Amendment to the Guaranty dated the date hereof
     from the Guarantors (as defined therein) for the benefit of the Collateral
     Agent (on behalf of the Original Purchasers and the Lender), and as such
     Guaranty is further amended from time to time) (the "Secured Obligations");
                                                          -------------------
     and the Grantors are each willing to grant to the Collateral Agent for the
     benefit of the Purchasers a security interest in all of its patents and
     trademarks; and"

          (c)  Section 1(a) of the Patent and Trademark Security Agreement is
hereby amended and restated in its entirety as follows:

          "Unless otherwise defined herein, each capitalized term used herein
     that is defined in the Purchase Agreement shall have the meaning specified
     for such term in the Purchase Agreement, except that (i) the term

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<PAGE>

     "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)."

     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 Company shall have satisfied all conditions to effectiveness under
Section 6 of the First Amendment.

     (c)  The Company 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), each Grantor hereby represents and warrants to the Original Purchasers
and the Lender that it has full power, right and legal authority to execute,
deliver and perform its obligations under this Amendment.  Each Grantor 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 each Grantor 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. Each Grantor hereby ratifies and reaffirms
the Patent and Trademark Security Agreement (as amended hereby) and the other
related documents and each of its respective covenants, duties and liabilities
thereunder.

     4.   U.S. Patent Office Filing.  The Grantors acknowledge that this
          -------------------------
Amendment shall be filed with the U.S. Patent Office and, at the sole discretion
of the Collateral Agent, may be filed in any other corresponding offices in
other countries and foreign jurisdictions through out the world.  Each Grantor
shall, in accordance with Section 16 and 21 of the Patent and Trademark
Agreement, pay all costs incurred by the Collateral Agent (on behalf of the
Original Purchasers and the Lender) with respect to this Amendment, including
without limitation, the cost of such filings and shall at its own expense do
such further acts and things, and to execute and deliver such additional
conveyances, assignments, financing statements, agreements and instruments, as
the Collateral Agent for the benefit of the Original Purchasers and the Lenders
may at any time reasonably request in connection with the administration or
enforcement of this Agreement.

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<PAGE>

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

     6.   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.

     7.   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).

     8    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.

     9.   Survival of the Security Agreement.  Each reference in the Patent and
          ----------------------------------
Trademark Security Agreement to "this Agreement," "hereunder," "hereof,"
"herein" or words of like import, and each reference to the Patent and Trademark
Security Agreement in any related document (other than the Patent and Trademark
Security Agreement) shall mean and be a reference to the Patent and Trademark
Security Agreement as amended hereby. Except as specifically amended by this
Amendment, the Patent and Trademark Security Agreement shall remain in full
force and effect and is hereby ratified, confirmed and acknowledged by each of
the Grantors. This Amendment shall not be deemed to (i) be a consent to any
waiver or modification of any term or condition of the Patent and Trademark
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 Patent and Trademark Security Agreement.

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

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<PAGE>

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

                              GRANTORS:
                              --------

                              SENETEK, PLC

                              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.

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

  [Signature page to the First Amendment to the Patent and Trademark Security
                                  Agreement]<PAGE>

                                                                   Exhibit 10.12

                          INVESTMENT ADVICE AGREEMENT

          This INVESTMENT ADVICE AGREEMENT (this "Agreement"), is dated as of
June 20, 2001, between Senetek PLC, a company organized under the laws of
England (the "Company") and Scorpion Holdings, Inc., a Delaware limited
liability company ("Scorpion").

          WHEREAS, the Company has executed the First Amendment to the
Securities Purchase Agreement (the "First Amendment"), dated as of June 20,
2001, by and among the Company and the Purchasers (as defined on Schedule 1
thereto);

          WHEREAS, the Company has executed the Revolving Credit Agreement (the
"Credit Agreement"), dated as of June 20, 2001, by and between the Company and
Wallington Investments, Inc. (the "Lender");

          WHEREAS, Scorpion has provided the Company with investment advice in
conjunction with both the First Amendment and the Credit Agreement;

          WHEREAS, in consideration for Scorpion's investment advice, the
Company wishes to pay Scorpion a Transaction Fee (as defined below) in
connection with the First Amendment and a Drawdown Fee (as defined below) in
connection with the Credit Agreement.

          NOW, THEREFORE, in consideration for the investment advice provided to
the Company by Scorpion, and for other good and valuable consideration, the
adequacy and receipt of which is hereby acknowledged, the Company and Scorpion
agree as follows:

          1.   Definitions.
               -----------

          All capitalized terms used but not defined herein have the meaning
assigned to them in the First Amendment and the Credit Agreement.

          2.   Transaction Fee from the First Amendment.
               ----------------------------------------

          (a)  The Company will pay Scorpion within 10 days of the date hereof a
one-time fee equal to five (5%) percent of the aggregate unpaid principal amount
of the Notes (as defined in the First Amendment) on the date hereof (the
"Transaction Fee"). Such Transaction Fee shall be paid by issuing that number of
Ordinary Shares as determined by a fraction, the numerator of which is the
Transaction Fee and the denominator of which is the 10-day average closing price
(for the 10 trading days prior to the date hereof) of the Company's American
Depository Shares ("ADSs") as quoted on any securities exchange or automated
quotation system on which the ADSs may be listed or quoted (the "Transaction Fee
Shares"); provided, however, that in no event shall Ordinary Shares be issued
for less than their nominal value. The Company hereby agrees to pay all stamp
duty reserve taxes, fees to Depositary and all other fees and expenses
associated with converting such Transaction Fee Shares into ADSs in registered
form.
<PAGE>

          (b)  Pursuant to the calculation in Section 2(a) above the Transaction
Fee to be paid by the Company to Scorpion within 10 days of the date hereof
equals Three Hundred Forty-One Thousand Seven Hundred Forty-Seven (341,747)
Ordinary Shares.

          3.   Drawdown Fee from the Credit Agreement.
               --------------------------------------

          The Company shall pay a drawdown fee to Scorpion on the date of each
Borrowing (as defined in the Credit Agreement) equal to five (5%) percent of the
principal amount of such Borrowing (the "Drawdown Fee"); provided, however, that
in no event shall the aggregate amount of all Drawdown Fees paid hereunder
exceed $50,000.  Such Drawdown Fee shall be paid, at the Company's discretion to
Scorpion (an affiliate of the Lender), either (i) in cash or (ii) by issuing
that number of Ordinary Shares as determined by a fraction, the numerator of
which is the Drawdown Fee and the denominator of which is the 10-day average
closing price (for the 10 trading days prior to the date of such Borrowing) of
the Company's ADSs as quoted on any securities exchange or automated quotation
system on which the ADSs may be listed or quoted (the "Drawdown Fee Shares");
provided, however, that in no event shall Ordinary Shares be issued for less
than their nominal value.  In the event that the Company elects to pay the
Drawdown Fee by issuing Drawdown Fee Shares, as provided in clause (ii) of the
preceding sentence, the Company hereby agrees to pay all stamp duty reserve
taxes, fees to the depositary and all other fees and expenses associated with
converting the Fee Shares into ADSs in registered form.

          4.   Representations of the Company.
               ------------------------------

          The Company hereby confirms as of the date hereof, all of the
representations and warranties made by the Company in the First Amendment and
the Credit Agreement.

          5.   Representations of Scorpion.
               ---------------------------

          Scorpion represents and warrants to the Company as follows:

               (a)  Authorization.  Scorpion has full power and authority to
                    -------------
enter into this Agreement. This Agreement has been duly authorized, executed and
delivered by Scorpion and constitutes its valid and legally binding obligation,
enforceable in accordance with its terms. Neither the execution, delivery of
performance by this Agreement by Scorpion nor the consummation by Scorpion of
the transactions contemplated hereby will result in a violation of, conflict
with, or result in any breach of any of the terms of, or constitute a default
under, any provision of federal, state or local law or foreign law to which
Scorpion is subject, the organizational documents of Scorpion or any mortgage,
indenture, agreement, instrument, judgment, decree, order, rule or regulation or
other restriction to which Scorpion is a party or by which it is bound.

               (b)  Purchase Entirely for Own Account. This Agreement is made
                    ---------------------------------
with Scorpion in reliance upon Scorpion's representation to the Company, which
by Scorpion's execution of this Agreement Scorpion hereby confirms, that the
ADSs, Transaction Fee Shares and Drawdown Fee Shares issuable as contemplated by
this Agreement, (collectively, the "Acquired Securities") will be acquired for
investment for Scorpion's own account, not as a nominee or agent, and not with a
view to the resale or distribution of any part of the Acquired
<PAGE>

Securities in contravention of applicable law, and that Scorpion has no present
intention of selling, granting any participation in, or otherwise distributing
the same. Scorpion does not have any contract, undertaking, agreement or
arrangement with any person to sell, transfer or grant participation to such
person or to any third person in or with respect to any of the Acquired
Securities.

               (c)  Accredited Investor.  Scorpion is, and upon the acquisition
                    -------------------
of the Acquired Securities will be, an "accredited investor" within the meaning
of Rule 501 of Regulation D of the Rules and Regulations of the Securities and
Exchange Commission under the Securities Act of 1933, as amended (the
"Securities Act"). Scorpion has not been organized for the purposes of acquiring
the Acquired Securities.

               (d)  Restricted Securities.  Scorpion understands that the
                    ---------------------
Acquired Securities it is acquiring and may acquire as contemplated by this
Agreement are "restricted securities" within the meaning of Rule 144 under the
Securities Act ("Rule 144") inasmuch as they will be acquired from the Company
in a transaction not involving a public offering and that under the federal
securities laws and applicable regulations such Acquired Securities may be
resold without registration under the Securities Act only in certain limited
circumstances. In this connection, Scorpion represents that it is familiar with
Rule 144 and understands the resale limitations imposed thereby and by the
Securities Act. Scorpion acknowledges that its investment in the Acquired
Securities may be an illiquid investment requiring Scorpion to bear the economic
risk of the investment for an indefinite period.

               (e)  Further Limitations on Disposition.  Without in any way
                    ----------------------------------
limiting the representations set forth above, Scorpion further agrees not to
make any disposition of all or any portion of the Acquired Securities unless and
until the transferee has agreed in writing for the benefit of the Company to be
bound by the terms of this Section 5 (provided and to the extent that such terms
are then applicable and provided that Scorpion is making such disposition in a
transaction other than pursuant to Rule 144 or under an effective registration
statement under the Securities Act and in accordance with any applicable state
securities laws), and

               (i)  Scorpion shall have notified the Company of the proposed
     disposition, and

               (ii) If requested by the Company, Scorpion shall have furnished
     the Company with an opinion of counsel, in form and substance reasonably
     satisfactory to the Company, rendered by a law firm experienced in matters
     involving the sale of securities under federal and state securities laws,
     that such disposition will not require registration of the Acquired
     Securities under the Securities Act or registration or qualification under
     any state securities or "blue sky" law.

               (f)  Legends.  It is understood that the certificates evidencing
                    -------
the Acquired Securities will bear an appropriate legend restricting transfers
substantially in the following form:

          "THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE
          SECURITIES ACT OF 1933, AS AMENDED (THE "ACT")
<PAGE>

          OR ANY APPLICABLE STATE SECURITIES LAWS. THEY MAY NOT BE
          SOLD OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE
          ABSENCE OF A REGISTRATION STATEMENT IN EFFECT WITH RESPECT
          TO THE SECURITIES UNDER THE ACT AND THE REGISTRATION OR
          QUALIFICATION OF THE SECURITIES UNDER APPLICABLE STATE
          SECURITIES LAWS OR AN OPINION OF COUNSEL REASONABLY
          SATISFACTORY TO THE COMPANY, IN FORM AND CONTENT REASONABLY
          SATISFACTORY TO THE COMPANY, THAT REGISTRATION OR
          QUALIFICATION UNDER THE ACT AND STATE SECURITIES LAWS IS NOT
          REQUIRED."

               (g)  Consents.  To Scorpion's knowledge, no consent, approval or
                    --------
authorization of or designation, declaration or filing with any state, federal
or foreign governmental authority on the part of Scorpion is required in
connection with the valid execution and delivery of this Agreement and the
consummation of the transactions contemplated hereby.

               (h)  Disclosure of Information. The Lender represents that it has
                    -------------------------
had an opportunity to ask questions and receive answers form the Company
regarding the Company and its business and prospects and the terms and
conditions of the sale of the Acquired Securities.

          7.   Covenant of the Company.
               -----------------------

          The Company covenants and agrees that it will at all times reserve and
set apart and have, free from preemptive rights, a number of shares of
authorized but unissued Ordinary Shares sufficient to enable it at any time to
fulfill all of its obligations hereunder.  The issuance of such shares has been
duly and validly authorized, and when issued and sold in accordance with this
Agreement, such shares will be duly and validly issued, fully paid and
nonassessable.

          8.   Governing Law.
               -------------

          This Agreement shall be governed by the laws of the State of New York.

                         Signatures on Following Page
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed this Investment
Advice Agreement as of the day and year first set forth above.

                                    SENETEK PLC

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

                                    SCORPION HOLDINGS, INC.

                                    By: /s/ N. Brandolini
                                        -----------------
                                    Name:  N. Brandolini
                                    Title: CEO

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