Document:

<PAGE>   1
                                                                    EXHIBIT 10.5

                              EMPLOYMENT AGREEMENT

         This EMPLOYMENT AGREEMENT (the "AGREEMENT") is made and entered into
this 16th day of October, 1993, by and between ZONAGEN, INC., a Delaware
corporation (hereinafter referred to as the "COMPANY," which term shall for all
purposes be deemed to include its successors and assigns), and LOUIS PLOTH, JR.
(the "EXECUTIVE").

                                   WITNESSETH

         WHEREAS, the Company desires to employ the Executive as its Chief
Financial Officer on the terms and subject to the conditions set forth herein,
and the Executive desires to accept such employment.

         NOW, THEREFORE, in consideration of the mutual covenants, promises and
agreements contained herein, and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, the parties hereto
agree as follows:

         1.       EMPLOYMENT.

                  (a)      The Company hereby employs the Executive and the
                           Executive hereby accepts employment as the Chief
                           Financial Officer of the Company, subject to the
                           direction of the Board of Directors and the Company's
                           officers designated by the Board of Directors, and
                           shall perform and discharge well and faithfully the
                           duties and responsibilities that are assigned to him
                           by the Board of Directors. The Executive agrees to
                           devote such of his time, attention and energy to the
                           business of the Company, and any of its subsidiaries
                           or affiliates, as may be required to perform the
                           duties and responsibilities assigned to him by the
                           Board of Directors to the best of his ability and
                           with requisite diligence. If the Executive is
                           appointed a director or elected to another executive
                           officer position of the Company or any subsidiary
                           thereof during the term of this Agreement, the
                           Executive will serve in such capacity without further
                           compensation.

                  (b)      The Executive agrees to comply in all material
                           respects, at all times during the Executive Period
                           (as defined in Section 2 hereof), with all applicable
                           policies, rules and regulations of the Company.

         2.       TERM. Subject to the terms hereof, this Agreement shall
                  commence on the date hereof (the "EXECUTION DATE") and shall
                  terminate on the second anniversary of the Execution Date;
                  provided, that this Agreement will automatically renew for
                  successive one-year periods unless written notice of
                  termination is given to the Executive by the Company not less
                  than sixty (60) days before the expiration of the term hereof
                  or any renewal period then in effect. The term of this
                  Agreement shall include any such renewal periods and shall be
                  referred to herein as the "EXECUTIVE PERIOD."

<PAGE>   2

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 2 OF 7

         3.       COMPENSATION. For all services rendered under this Agreement,
                  the Company agrees to pay to Executive during the Executive
                  Period:

                  (i)    A base monthly salary of $7,916.00, payable in equal
                         semi-monthly installments or on any other periodic
                         basis consistent with the Company's payroll procedures,
                         subject only to such payroll and withholding deductions
                         as are required by applicable federal and state laws.

         4.       FRINGE BENEFITS: EXPENSES.

                  (a)      So long as the Executive is employed by the Company,
                           the Executive shall participate in all employee
                           benefit plans sponsored by the Company for its
                           executive employees, including, but not limited to,
                           vacation policy, health insurance, dental insurance
                           and pension or profit-sharing plans; provided,
                           however, that the nature, amount and limitations of
                           such plans shall be determined from time to time by
                           the Board of Directors of the Company.

                  (b)      The Company agrees to propose to the Compensation
                           Committee of the Board of Directors that the
                           Executive be granted stock options under the
                           Company's Amended and Restated 1993 Employee and
                           Consultant Stock Option Plan (the "Plan") to purchase
                           up to 25,000 shares of the Company's common stock,
                           par value $.01 per share (the "Common Stock"), at an
                           exercise price equal to the closing sale price of a
                           share of Common Stock, as reported by the NASDAQ
                           Market, on the date of grant (which date shall be no
                           later than the date of this Agreement), with such
                           option to (i) vest in accordance with the Company's
                           customary vesting schedule for stock options and (ii)
                           automatically vest in full on a Change in Control (as
                           defined in the Plan) of the Company.

                  (c)      The Company agrees to reimburse the Executive for all
                           reasonable out-of-pocket expenses incurred by him in
                           the performance of his duties, subject to the
                           submission of appropriate documentation in accordance
                           with the Company's expense reimbursement policy as in
                           existence from time to time.

         5.       CONFIDENTIAL INFORMATION AND NON- COMPETITION. The Executive
                  shall execute and comply with the Proprietary Information and
                  Inventions and Non-Competition Agreement in the form attached
                  as Exhibit A hereto and incorporated herein by reference.

<PAGE>   3

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 3 OF 7

         6.       TERMINATION.

                  (a)      At any time during the Executive Period, the Company
                           may, at its sole discretion, discharge the Executive,
                           with or without "cause". Such termination shall be
                           effective on delivery of written notice to the
                           Employee of the Company's election to terminate this
                           Agreement under this Section 6. For purposes of this
                           Agreement, the following events shall constitute
                           "CAUSE": (i) the conviction of the Executive by a
                           court of competent jurisdiction of a crime involving
                           moral turpitude; (ii) the commission, or attempted
                           commission, by the Executive of an act of fraud on
                           the Company; (iii) the misappropriation, or attempted
                           misappropriation, by the Executive of any funds or
                           property of the Company; (iv) the continued and
                           unreasonable failure by the Executive to perform in
                           any material respect his obligations under the terms
                           of this Agreement; (v) the knowing engagement by the
                           Executive, without the written approval of the Board
                           of Directors, in any direct, material conflict of
                           interest with the Company without compliance with the
                           Company's conflict of interest policy; (vi) the
                           knowing engagement by the Executive, without the
                           written approval of the Board of Directors, in any
                           activity which competes with the business of the
                           Company or which would result in a material injury to
                           the Company; or (vii) the knowing engagement by the
                           Executive in any activity that would constitute a
                           material violation of the provisions of the Company's
                           Insider Trading Policy or Business Ethics Policy, if
                           any, then in effect.

                           If the Company terminates the Executive's employment
                           under this Agreement for reasons other than Cause,
                           then the Company shall, subject to the terms of this
                           Section 6, pay to the Employee (or his estate or
                           representative, as appropriate) an amount equal to
                           six (6) months compensation at his then current
                           salary, payable bi-monthly or in accordance with the
                           Company's payroll procedures, and shall continue to
                           provide benefits in the kind and amounts provided up
                           the date of termination for the 6-month period,
                           including, without limitation, continuation of any
                           Company-paid benefits as described in Section 5 of
                           this Agreement for the Executive and his family.
                           Under no circumstances shall the Executive be
                           entitled to any compensation or continuation of
                           benefits for any period of time following his
                           termination if his termination is for Cause. If the
                           Company terminates the Executive's employment under
                           this Agreement for reasons other than Cause, the
                           Executive agrees to accept, in full settlement of any
                           and all claims, losses, damages and other demands
                           that the Executive may have arising out of such
                           termination as liquidated damages and not as a
                           penalty, the six-month salary payments and
                           continuation of Company-paid benefits as set forth
                           above. The

<PAGE>   4

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 4 OF 7

                           Executive hereby waives any and all rights that he
                           may have to bring any cause of action or proceeding,
                           as a result of such termination, except to enforce
                           the Company's obligation to pay amounts owing
                           pursuant to this Section 6.

                  (b)      This Agreement will terminate automatically on the
                           earliest to occur of: (i) the death or disability of
                           the Executive; (ii) the voluntary retirement of the
                           Executive; or (iii) the expiration of the Executive
                           Period unless otherwise renewed.

                  (c)      If at any time during the term of this Agreement, the
                           Executive is unable to perform effectively his duties
                           hereunder because of physical or mental disability,
                           the Company shall continue payment of compensation as
                           provided in Section 3 hereof during the first
                           six-month period of such disability to the extent not
                           covered by the Company's disability insurance
                           policies. On the expiration of such six-month period,
                           the Company, at its sole discretion, may continue
                           payment of the Executive's salary for such additional
                           periods as the Company elects or may terminate this
                           Agreement without any further obligations thereunder.
                           If the Executive should die during the term of this
                           Agreement, the Executive's employment and the
                           Company's obligations hereunder shall terminate as of
                           the last day of the month in which the Executive's
                           death occurs.

                  (d)      Notwithstanding the terms of Section 6(a) above, the
                           Executive shall be obligated to actively pursue
                           employment following termination of his employment to
                           be entitled to be paid the continuation of salary
                           provided in Section 6(a), and the Company's
                           obligation to pay any such continuation of salary
                           shall terminate at such time as the Executive
                           commences employment with another employer; provided,
                           however, that nothing herein shall obligate the
                           Executive to pursue or accept employment for a
                           position that is not commensurate with his current
                           position at the Company or otherwise acceptable to
                           him.

                  (e)      At any time during the term of this Agreement, the
                           Executive may terminate this Agreement by giving at
                           least thirty days written notice to the Company of
                           his intent to terminate this Agreement, with the date
                           of termination to be specified in such notice.

                  (f)      If this Agreement is terminated by the Executive
                           pursuant to Section 6(e) hereof, then the Company
                           will have no obligation to pay any amount to the
                           Executive other than amounts earned or accrued
                           pursuant to Section 3 hereof, but which have not yet
                           been paid, as of the date of termination.

<PAGE>   5

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 5 OF 7

         7.       ASSIGNMENT BY EXECUTIVE. Except as otherwise expressly
                  provided herein, the Executive agrees for himself, and on
                  behalf of his executors and administrators, heirs, legatees,
                  distributees and any other person or persons claiming any
                  benefits under him by virtue of this Agreement, that this
                  Agreement and the rights, interests and benefits hereunder
                  shall not be assigned, transferred, pledged or hypothecated in
                  any way by the Executive or any executor, administrator, heir,
                  legatee, distributee or person claiming under the Executive by
                  virtue of this Agreement and shall not be subject to
                  execution, attachment or similar process. Any attempt at
                  assignment, transfer, pledge or hypothecation or other
                  disposition of this Agreement or of such rights, interests and
                  benefits contrary to the foregoing provision, or the levy of
                  any attachment or similar process thereupon, shall be null and
                  void and without effect.

         8.       SUCCESSORS OF THE COMPANY. This Agreement shall be binding on
                  and inure to the benefit of any Successor (as hereinafter
                  defined) of the Company and any such Successor shall be deemed
                  substituted for the Company under the terms of this Agreement.
                  As used in this Agreement, the term "SUCCESSOR" shall include
                  any person, firm, corporation or other business entity which
                  at any time, whether by merger, purchase or otherwise,
                  acquires all or substantially all of the assets or businesses
                  of the Company; but no such substitution shall relieve such
                  companies of their original obligations hereunder. This
                  Agreement may not otherwise be assigned by the Company without
                  the Executive's consent to any person, firm, corporation,
                  limited liability company, trust or other entity.

         9.       NOTICES. All notices or other communications that are required
                  or may be given under this Agreement shall be in writing and
                  shall be deemed to have been duly given when delivered in
                  person, transmitted by telecopier or mailed by registered or
                  certified first class mail, postage prepaid, return receipt
                  requested, to the parties hereto at the address set forth
                  below (as the same may be changed from time to time by notice
                  similarly given) or the last known business or residence
                  address of such other person as may be designated by either
                  party hereto in writing.

<PAGE>   6

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 6 OF 7

                                    If to the Company:

                                    Zonagen, Inc.
                                    2408 Timberloch Place, Suite B-4
                                    The Woodlands, Texas  77380
                                    Attn:  Joseph S. Podolski

                                    If to the Executive:

                                    Louis Ploth, Jr.
                                    Route 25, Box 110
                                    Ponderosa Pines
                                    Conroe, Texas  77385

         10.      WAIVER OF BREACH. A waiver by the Company or the Executive of
                  a breach of any provision of this Agreement by the other party
                  shall not operate or be construed as a waiver of any other
                  breach by the other party.

         11.      GOVERNING LAW. This Agreement shall be governed by and
                  construed in accordance with the laws of the State of Texas.

         12.      SEVERABILITY. If any provision of this Agreement shall, for
                  any reason, be held to violate any applicable law, and so much
                  of said Agreement is held to be unenforceable, then the
                  invalidity of such specific provision herein shall not be held
                  to invalidate any other provision herein which shall remain in
                  full force and effect.

         13.      AMENDMENT. This Agreement constitutes and contains the entire
                  agreement of the parties and supersedes any and all prior
                  negotiations, correspondence, understandings and agreements
                  between the parties respecting the subject matter hereof. This
                  Agreement may be modified only by an agreement in writing
                  executed by all the parties hereto.

         14.      HEADINGS. The section and subsection headings contained in
                  this Agreement are for reference purposes only and shall not
                  affect in any way the meaning or interpretation of this
                  Agreement.

         15.      COUNTERPARTS. This Agreement may be executed in any number of
                  counterparts, each of which shall be deemed an original, and
                  all of which together shall constitute one instrument.

         16.      CUMULATIVE REMEDIES. All rights and remedies hereunder are
                  cumulative and are in addition to all other rights and
                  remedies provided by law, agreement or otherwise.

<PAGE>   7

EMPLOYMENT AGREEMENT
LOUIS PLOTH, JR.

PAGE 7 OF 7

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
of the date first written above.

                                  COMPANY:

                                  ZONAGEN, INC.

                                  /s/  Joseph S. Podolski
                                  ------------------------------------------
                                       Joseph S. Podolski
                                       President and Chief Executive Officer

                                  EXECUTIVE:

                                  /s/   Louis Ploth, Jr.
                                  ------------------------------------------
                                        Louis Ploth, Jr.<PAGE>   1
                                                                   EXHIBIT 10.22

                                 FIRST AMENDMENT
                                     TO THE
                                  ZONAGEN, INC.
                   AMENDED AND RESTATED 1993 STOCK OPTION PLAN

This First Amendment (the "Amendment") to the Zonagen, Inc. (the "Company")
Amended and Restated 1993 Employee and Consultant Stock Option Plan (the "Plan")
is executed pursuant to Section 14 of the Plan. All capitalized and undefined
terms used herein shall have the meanings ascribed to such terms in the Plan.

         WHEREAS, the Company's Board of Directors (the "Board") is authorized
by Section 14 of the Plan to amend the Plan from time to time, subject to any
required stockholder approval of any such amendments; and

         WHEREAS, at a meeting on March 5, 1999 the Board approved (i) setting
the number of shares of the Company's common stock, par value $.001 per share
(the "Common Stock"), for which options may be granted under the Plan at
2,000,000 shares and (ii) extending the term of the Plan to May 13, 2003; and

         WHEREAS, at a meeting held on May 13, 1999, the Company's stockholders
approved the Amendment.

         NOW, THEREFORE, in order to amend Sections 3 and 19 of the Plan as
authorized by the Board and approved by the stockholders:

         1.       The second paragraph of Section 3 of the Plan is hereby
                  revised in its entirety to read as follows:

                  "The Committee may grant Options, shares of Restricted Stock
                  and Stock Bonuses under the Plan with respect to a number of
                  shares of Common Stock that in the aggregate does not exceed
                  2,000,000. The Company will, during the term of this Plan,
                  reserve and keep available for issuance a sufficient number of
                  shares of Common Stock to satisfy the requirements of the
                  Plan."

         2.       The last sentence of Section 19 of the Plan is hereby revised
                  in its entirety to read as follows:

                  "No Options, shares of Restricted Stock or Stock Bonuses may
                  be granted under the Plan after May 13, 2003."

         3.       Except as amended hereby, the terms and provisions of the Plan
                  shall remain in full force and effect, and the Plan and this
                  Amendment shall be read, taken and construed as one and the
                  same instrument.

         IN WITNESS WHEREOF, and as conclusive evidence of the adoption of the
foregoing Amendment to the Plan by the Board of the Company and approval and
adoption thereof by the stockholders of the Company, the Company has caused this
Amendment to be duly executed in its name and behalf by its proper officers
thereunto duly authorized as of the 13th day of May, 1999.

                                        ZONAGEN, INC.

                                        By:    /s/  F. Scott Reding
                                           ------------------------------
                                        Name:  F. Scott Reding
                                             ----------------------------
                                        Title: CFO
                                              ---------------------------

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00006-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00006-of-00352.parquet"}]]