<PAGE>


                                                                   Exhibit 4.4.3
                                                                   -------------

  THIRD AMENDMENT TO CREDIT AGREEMENT AND LOAN DOCUMENTS AND WAIVER OF DEFAULTS
  -----------------------------------------------------------------------------

         This Third Amendment to Credit Agreement and Loan Documents and Waiver
of Defaults (this "Agreement") is entered into as of January 25, 2002 by and
between COMERICA BANK - CALIFORNIA, successor in interest to Imperial Bank, a
California banking corporation, ("Bank") and SYNBIOTICS CORPORATION, a
California corporation, ("Borrower"). This Agreement is made with reference to
the following facts:

                                    RECITALS
                                    --------

         A.  Borrower is currently indebted to Bank pursuant to the Loan
Documents (as defined below). Borrower acknowledges that it is in default under
the Loan Documents as set forth in Section I.C. below, and Borrower desires,
inter alia, that Bank restructure Borrower's payment obligations and waive the
----- ----
specified defaults in exchange for certain financial accommodations to be
provided to Borrower by Redwood West Coast, LLC ("Redwood") (as defined below).

         B.  Bank is willing to waive such defaults and restructure Borrower's
payment obligations only to the degree set forth herein, and only in accordance
with the terms and conditions set forth in this Agreement.

         C.  THIS AGREEMENT ADDRESSES THE DEBTS AND/OR OBLIGATIONS OF BORROWER
TO BANK WHICH ARE FULLY DESCRIBED HEREIN. THIS AGREEMENT DOES NOT PERTAIN TO ANY
OTHER INDEBTEDNESS AND/OR OBLIGATIONS OF BORROWER (OR ANY OTHER PARTIES) TO BANK
NOT SPECIFICALLY ADDRESSED IN THIS AGREEMENT. ALL TERMS AND PROVISIONS OF ANY
AGREEMENTS BETWEEN BORROWER AND BANK INCLUDING, BUT NOT LIMITED TO, THE LOAN
DOCUMENTS, NOT SPECIFICALLY MODIFIED HEREIN, SHALL REMAIN IN FULL FORCE AND
EFFECT IN ACCORDANCE WITH THEIR ORIGINAL TERMS.

                                    AGREEMENT
                                    ---------

         NOW, THEREFORE, in consideration of (i) the above recitals and the
mutual promises contained in this Agreement; (ii) the execution of this
Agreement and all documents, instruments and agreements required to be executed
in accordance with this Agreement; (iii) the satisfaction of all Conditions
Precedent set forth in Section VIII. below; and (iv) other and further valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, it
is hereby agreed as follows:

         I.  Acknowledgment Of The Existing Indebtedness And The Loan Documents.
             ------------------------------------------------------------------

         A.  The Credit Agreement and Other Loan Documents.
             ---------------------------------------------

             1. On or about April 12, 2000, Borrower and Bank entered into that
         certain Credit Agreement (as amended, restated, modified, supplemented
         or revised from time to time, the "Credit Agreement"), pursuant to
         which Borrower promised to pay Bank the principal amount of up to Ten
         Million Dollars ($10,000,000.00), together with interest on the funds

                                       -1-

<PAGE>

         disbursed thereunder at the rate provided for in the promissory notes
         described below. The Credit Agreement was amended pursuant to a First
         Amendment to Credit Agreement dated as of April 18, 2000 ("First
         Amendment"), and by a Second Amendment to Credit Agreement dated as of
         November 14, 2000 ("Second Amendment").

                2. Pursuant to the Credit Agreement, Borrower executed and
         delivered to Bank a (a) Promissory Note in the principal amount of Six
         Million Dollars ($6,000,000.00) (as amended, restated, modified,
         supplemented or revised from time to time, the "Term Note") and a (b)
         Revolving Note in the principal amount of Four Million Dollars
         ($4,000,000.00) (as amended, restated, modified, supplemented or
         revised from time to time, the "Revolving Note"). Pursuant to the
         Second Amendment, Borrower executed and delivered to Bank a new Term
         Note in the principal amount of Six Million Three Hundred Thousand
         Dollars ($6,300,000.00) (The Term Note and Revolving Note, as amended,
         restated, modified, supplemented or revised from time to time, are
         referred to herein collectively as the "Notes").

                3. Also pursuant to the Credit Agreement: (a) Borrower executed
         and delivered to Bank: (i) that certain Commercial Security Agreement
         dated as of April 12, 2000 (as amended, restated, modified,
         supplemented or revised from time to time, the "Commercial Security
         Agreement"); (ii) that certain Commercial Pledge and Security Agreement
         dated as of April 12, 2000 (as amended, restated, modified,
         supplemented or revised from time to time, the "Commercial Pledge
         Agreement"); (iii) that certain Patent Security Agreement dated as of
         April 12, 2000 (as amended, restated, modified, supplemented or revised
         from time to time, the "Patent Security Agreement"); and (iv) that
         certain Trademark Security Agreement dated as of April 12, 2000 (as
         amended, restated, modified, supplemented or revised from time to time,
         the "Trademark Security Agreement"); and (b) W3Commerce LLC, a Delaware
         limited liability company, executed and delivered to Bank a Commercial
         Security Agreement dated as of April 12, 2000 (as amended, restated,
         modified, supplemented or revised from time to time, the "W3C
         Commercial Security Agreement"). The Credit Agreement, Commercial
         Security Agreement, Commercial Pledge Agreement, Patent Security
         Agreement, Trademark Security Agreement and W3C Commercial Security
         Agreement each grant Bank a valid, perfected, first priority security
         interest in the property described therein as collateral (the
         "Collateral") securing the Borrower's obligations to Bank under the
         Loan Documents.

                4. On or about April 12, 2000, Borrower executed and delivered
         to Bank two form UCC-1 financing statements. Bank filed the financing
         statements with the office of the Secretary of State of California.
         Bank has filed the Patent Security Agreement and the Trademark Security
         Agreement with the United States Patent and Trademark Office.

                5. Borrower has delivered to Bank a warrant to purchase stock
         dated December 1, 2000 granting to Bank stock warrants in Borrower for
         a total of 250,000 shares of Borrower's Common Stock, on terms and
         conditions more fully set forth therein.

                6. The documents referenced above and all documents, security
         agreements and written amendments, notes and so forth related thereto
         are hereinafter collectively referred to as "Loan Documents." Upon
         execution and delivery of the Amended Promissory Note (defined below),
         it shall be deemed one of the Loan Documents. All capitalized terms not
         defined herein shall have the meaning described in the Loan Documents.

                                       -2-

<PAGE>

              7. The Borrower acknowledges that the Loan Documents constitute
         duly authorized, valid, binding, fully perfected and continuing
         agreements and obligations of Borrower to Bank, enforceable in
         accordance with their respective terms; and that Borrower has no
         claims, cross-claims, counterclaims, setoffs or defenses of any kind or
         nature which would in any way reduce or offset its obligations to Bank
         under the Loan Documents as of the date of this Agreement.

         B.   Existing Indebtedness. Borrower acknowledges and agrees that the
              ---------------------
current outstanding principal balance owed to Bank under the Loan Documents is
Seven Million One Hundred and Thirty-two Thousand Dollars ($7,132,000.00) (the
"Existing Principal Amount"). The amount owed under the Loan Documents includes
the Existing Principal Amount, plus interest accrued thereon from December 31,
2001 to January 25, 2002 in the amount of Thirty-Four Thousand Four Hundred
Seventy-One and 33/100s Dollars ($34,471.33), together with the Bank's costs,
expenses and reasonable attorneys' fees (collectively, the "Existing
Indebtedness"). The Existing Principal Amount shall be evidenced by the Amended
Promissory Note (defined below). All attorneys' fees and costs incurred by Bank
through and including January 25, 2002, in an amount not exceeding One Hundred
Sixty Thousand Dollars ($160,000.00), and all interest accrued to January 25,
2002, shall be paid by Borrower upon execution of this Agreement.

         C.   Defaults Under Credit Agreement and Other Loan Documents;
              ---------------------------------------------------------
Remedies.
--------
Borrower acknowledges and agrees that Borrower is in default under the terms and
conditions of the Loan Documents in that, inter alia, Borrower failed to:
                                          ----- ----
maintain compliance with financial covenants and to eliminate over advances
(collectively, the "Defaults"). Borrower acknowledges and agrees that but for
this Agreement, the Bank is fully entitled to exercise all of its rights and
remedies under the Loan Documents, including but not limited to foreclosing on
its Collateral. Borrower has no defense at law or equity, including the right of
setoff, to the Bank's claims for repayment of the Existing Indebtedness.

         II.  Limited Scope of Agreement. Nothing contained in this Agreement
              --------------------------
shall be interpreted as or be deemed a release or a waiver by Bank of any of the
terms and conditions of the Loan Documents, or any other documents, instruments
and agreements between the parties hereto except as specifically provided in
this Agreement. Unless specifically modified herein, all other terms and
provisions of the Loan Documents shall remain in full force and effect in
accordance with their original terms, and are hereby ratified and confirmed in
all respects. This Agreement does not constitute a waiver or release by Bank of
any obligations between Borrower and Bank, or a waiver by Bank of any defaults
by Borrower under the Loan Documents, unless expressly so provided herein, nor
between Bank and any other person or entity. The Bank has no duty to advance any
funds under the Loan Documents.

         III. Waiver of Defaults.  Subject to, and effective upon, satisfaction
              ------------------
of the Conditions Precedent set forth in section VIII. hereof:

         A.   Bank hereby waives all past defaults, including without limitation
those described in Section I.C. of this Agreement.

         B.   Borrower acknowledges and agrees that Bank's waiver of Defaults
set forth immediately above concerns only Borrower's Defaults identified in
Section I.C. hereof as existing as of the date of execution of this Agreement
("Existing Defaults"), but not as to any defaults

                                       -3-

<PAGE>

which may arise in the future, or which are unknown to Bank, or which are not
specified in Section I.C. hereof.

         IV.  Amendments to Credit Agreement and Other Loan Documents. Subject
              -------------------------------------------------------
to, and effective upon, satisfaction of the Conditions Precedent set forth in
section VIII. hereof:

         A.   Section 1.01 of the Credit Agreement specifying the Term Loan
Commitment is deleted and replaced with the following:

              1.01  Term Loan Commitment.

              (a)   Subject to the terms and conditions of this Agreement,
         Borrower's Existing Indebtedness shall be consolidated into, and
         evidenced by, an amended and restated Promissory Note in the form
         attached hereto as Exhibit A (the "Amended Promissory Note"). The
         principal amount of the Amended Promissory Note shall be equal to the
         Existing Principal Amount. The interest rate, maturity date and other
         terms of the Term Loan are set forth in the Amended Promissory Note.

              (b)   Notwithstanding the foregoing, Borrower shall make the
         following principal reduction in addition to the principal payments
         specified in the Amended Promissory Note: Borrower shall pay an
         additional principal payment equal to one-half (50%) of the amount by
         which Borrower's EBITDA for the year 2002 exceeds the sum of Four
         Million Dollars ($4,000,000.00). Such additional principal payment
         shall be made by the earlier of March 31, 2003 or the date Borrower
         files its audited financial statements with the United States
         Securities and Exchange Commission. For purposes of this provision,
         "EBITDA" shall be calculated without inclusion of gains or losses
         occurring upon the sale of assets outside the ordinary course of
         business.

         B.   Section 1.02 of the Credit Agreement specifying the Asset Based
Line of Credit Commitment is hereby deleted in its entirety.

         C.   Section 1.07 of the Credit Agreement concerning Applicable Margin
is hereby deleted in its entirety and replaced with the following:

              1.07  Financing Statements. Borrower hereby authorizes Bank to
         execute and file any financing statement Bank deems reasonably
         necessary for the perfection and/or preservation of Bank's security
         interests in the Collateral.

         D.   Sections 4.05(i), 4.06, 4.07, 4.08 and 4.09 of the Credit
Agreement concerning certain reporting requirements and financial covenants are
hereby deleted in their entirety.

         E.   Section 4.16 of the Credit Agreement concerning asset sales is
amended by deleting the final sentence and replacing it with the following:

         Bank shall apply such net cash proceeds first toward the remaining
         principal reductions due under the Amended Promissory Note in inverse
         order of maturity; provided, however, that upon the occurrence of an
         Event of Default, Bank shall have the right to apply such net cash
         proceeds in its sole and absolute discretion.

         F.   Section 5.05 of the Credit Agreement is amended by adding the
following to the existing text:

                                       -4-

<PAGE>

         Notwithstanding the foregoing, nothing in this Agreement shall
         prohibit, restrict or otherwise limit Borrower's right to issue Two
         Thousand Eight Hundred (2,800) shares of preferred stock to Redwood in
         exchange for cash consideration not less than Two Million Eight Hundred
         Thousand Dollars ($2,800,000.00).

         G.   Section 5.06 of the Credit Agreement is amended by deleting "One
Million Dollars ($1,000,000)" and inserting in lieu thereof "Five Hundred
Thousand Dollars ($500,000.00)".

         H.   Section 5.08 of the Credit Agreement is amended by adding the
following to the existing text:

         Notwithstanding the foregoing, nothing in this Agreement shall prohibit
         Borrower from paying dividends on preferred stock held by Redwood;
         provided, however, that no such dividends shall be paid while there is
         an Event of Default under this Agreement or any condition, act or event
         which, with the passage of time or the giving of notice or both would
         constitute an Event of Default under this Agreement; and further
         provided, however, that the maximum amount of such dividends that may
         be paid in any calendar quarter shall not exceed the sum of
         $240,000.00.

         I.   Section 7.11 of the Credit Agreement concerning the reference
procedure is deleted in its entirety.

         J.   All references in the Loan Documents to the "Note" or the
"Promissory Note" (singular or plural), other than such references in this
Agreement, shall include the Amended Promissory Note. All references in the Loan
Documents to the "Loan Documents" shall mean the Loan Documents including this
Agreement and the Amended Promissory Note. All references in the Loan Documents
to the "Related Documents" shall mean the Related Documents including this
Agreement and the Amended Promissory Note. All references in the Loan Documents
to the "Indebtedness" shall include the indebtedness owing under the Amended
Promissory Note.

         V.   Other Covenants.
              ----------------

         A.   Borrower shall not make any payments or transfer any consideration
to Redwood or any affiliate of Redwood not authorized by this Agreement or
consented to by Bank, in writing, in its sole and absolute discretion.

         B.   Borrower shall not make any payments or transfer any consideration
to any affiliate of Redwood unless such affiliate has consented to this
Agreement in the form attached hereto as Exhibit B.

         C.   Subject to the foregoing, Borrower may pay Redwood and/or its
affiliates fees for management services in a total amount not exceeding
$15,000.00 (collectively) per month, or such greater amount as Bank shall agree
in writing, in its sole and absolute discretion; provided, however, Borrower
shall not pay any amounts to Redwood and/or its affiliates for management
services while there is an Event of Default under this Agreement or any
condition, act or event which, with the passage of time or the giving of notice
or both would constitute an Event of Default under this Agreement.

         D.   Borrower hereby authorizes Bank to collect all amounts due Bank
under any of the Loan Documents by charging Borrower's accounts at Bank.

                                       -5-

<PAGE>

         E.    Borrower shall provide to Bank all documents, instruments and
agreements that Bank may reasonably request.

         VI.   Reimbursement of Bank's Fees and Costs. Contemporaneous with the
               --------------------------------------
execution of this Agreement, Borrower shall pay Bank a loan documentation fee of
Two Thousand Five Hundred Dollars ($2,500.00). The loan documentation fee shall
not be applied to or reduce the Existing Indebtedness or the Amended Promissory
Note, or be credited to Bank's attorneys' fees and costs. The obligation
specified in this paragraph shall not in any way be construed as a warranty or
representation that Bank's attorneys' fees and other costs incurred in preparing
this Agreement and related documentation did not exceed or approximate Two
Thousand Five Hundred Dollars ($2,500.00).

         VII.  Affirmative Covenants.
               ---------------------

         A.    In addition to any covenants, which exist in the Loan Documents,
Borrower shall immediately give written notice to Bank in reasonable detail of:

               1.  Any change in the name of Borrower, or any company or
               partnership in which Borrower is a principal or retains a
               majority interest. Borrower shall give Bank thirty days prior
               written notification of any such change;

               2.  Any change in the state of Borrower's incorporation, or
               relocation of Borrower's chief executive office. Borrower shall
               give Bank thirty days prior written notification of any such
               change or relocation;

               3.  Any change in the present location of the Collateral referred
               to herein;

               4.  The occurrence of any Event of Default (as defined in Section
               XI. below), or any condition, event or act which, with the giving
               of notice or the passage of time or both, would constitute an
               Event of Default under this Agreement;

               5.  Any termination or cancellation of any insurance policy which
               Borrower is required to maintain, or any uninsured or partially
               uninsured loss through liability or property damage, or through
               fire, theft or other cause affecting the Collateral in excess of
               an aggregate sum of $100,000.00; and

               6.  Any litigation initiated by or against Borrower for an amount
               in excess of $50,000.00.

         B.    At any time and from time to time Borrower shall execute and
deliver such further instruments and take such further action as may reasonably
be requested by Bank to effect the purposes of this Agreement.

         VIII. Conditions Precedent.  This Agreement shall not be binding upon
               --------------------
Bank (including Bank's waiver of defaults and the restructuring of Borrower's
payment obligations) unless and until each of the following conditions precedent
("Conditions Precedent") are met, or are waived in writing by Bank:

         A.    Borrower shall have timely complied with and performed all of the
acts and/or conditions specifically identified as conditions precedent in this
Agreement;

                                       -6-

<PAGE>

         B.   Redwood shall have purchased preferred shares from Borrower with a
cash capital contribution of not less than Two Million Eight Hundred Thousand
Dollars ($2,800,000.00) which funds shall be in Borrower's accounts at Bank;

         C.   Borrower shall have paid all interest accrued under the Loan
Documents as of the date hereof;

         D.   Borrower shall have duly executed and delivered to Bank the
Amended Promissory Note in the form attached hereto as Exhibit A;

         E.   Borrower shall have paid Bank, in good and immediately available
funds, all attorneys' fees and costs incurred by Bank through and including
January 25, 2002, which Bank and Borrower hereby agree shall not exceed One
Hundred Sixty Thousand Dollars ($160,000.00);

         F.   Borrower shall have paid Bank the amount required under Section
VI. above;

         G.   Redwood shall have duly executed and delivered to Bank a consent
in the form attached hereto as Exhibit B;

         H.   Bank shall have received such other documents, instruments and
agreements, and obtained all necessary internal approvals as Bank shall have
requested prior to execution of this Agreement; and

         I.   Borrower shall have executed and delivered to Bank certified
copies of corporate resolutions authorizing the execution of this Agreement,
certificates of incumbency, good standing, and such other matters as Bank in its
sole and absolute discretion may require.

         IX.  Release of Claims.
              -----------------

         As additional consideration for Bank to enter into this Agreement,
Borrower, for itself, its executors, administrators, general partners, limited
partners, employees, representatives, shareholders, predecessors, subsidiaries
and/or affiliates, parents, heirs, trustees, trustors, beneficiaries,
successors-in-interest, transferees, assigns, officers, directors, managers,
servants, employees, insurers, trustors, trustees, underwriters, successors,
attorneys, and agents, now and in the future, and all persons acting by,
through, under or in concert with Borrower, hereby releases and discharges Bank,
and Bank's past, present and future administrators, affiliates, agents, assigns,
attorneys, directors, employees, executors, heirs, officers, parents, partners,
predecessors, representatives, parents shareholders, subsidiaries and
successors, and each of them; and each of their respective administrators,
affiliates, agents, assigns, attorneys, directors, employees, executors, heirs,
officers, parents, partners, predecessors, representatives, shareholders,
subsidiaries and successors, and each of them; and all persons acting by,
through, under or in concert with one or more of them, from any liabilities or
claims arising out of, related to or in any way connected any acts or omissions
of Bank relating in any way to the Loan Documents, this Agreement (except for
matters relating to the performance of this Agreement following the date of its
execution) and Borrower's financial relationship with Bank and its
predecessors-in-interest from the beginning of time through and including the
date of execution of this Agreement (collectively, "Released Matters").

                                       -7-

<PAGE>

         X.   Representations and Waivers Concerning Release Provisions.
              ---------------------------------------------------------

         Borrower understands and has been advised by its legal counsel of the
provisions of Section 1542 of the California Civil Code, which provides as
follows:

            A general release does not extend to claims which the creditor does
            not know or suspect to exist in his favor at the time of executing
            the release, which if known by him must have materially affected his
            settlement with the debtor.

Borrower understands and hereby waives the provisions of California Civil Code
Section 1542 and declares that it realizes it may have damages Borrower
presently knows nothing about and that, as to them, Bank has been released
pursuant to these release provisions. Borrower also declares that it understands
that Bank would not agree to enter into this Agreement if the release provisions
set forth above did not cover damages and their results which may not yet have
manifested themselves or may be unknown to or not anticipated at the present
time by Borrower.

         Borrower represents and warrants that Borrower is the owner of the
claims hereby compromised and that Borrower has not heretofore assigned or
transferred, nor purported to assign or transfer, to any person or entity
("Person") any of the Released Matters. Borrower further agrees to indemnify and
hold harmless Bank from all liabilities, claims, demands, damages, costs,
expenses, and attorneys' fees incurred by Bank as the result of any Person
asserting any such assignment or transfer of any rights or claims.

         XI.  Events of Default. In addition to any other Events of Default set
              -----------------
forth in this Agreement or the Loan Documents, an "Event of Default" shall exist
under this Agreement and under the Loan Documents if any one or more of the
following events occur:

         A.   All of the Conditions Precedent set forth in Section VIII. hereof
are not fully satisfied or waived, each in Bank's sole and absolute discretion,
on or before January 25, 2002; or

         B.   Borrower shall fail to pay any payment as provided herein within
five (5) days of its due date; or

         C.   Any representation or warranty made under or in connection with
this Agreement, or any certificate or statement furnished or made to Bank
pursuant thereto, shall prove to be untrue or misleading in any material respect
as of the date on which such representation or warranty is made; or

         D.   Borrower shall take any action to the effect that, or make any
claim that any Loan Document, including without limitation this Agreement,
is/are not legal, valid, binding agreements enforceable against any party
executing same; or attempt in any way to terminate or declare ineffective or
inoperative the same; or shall in any way whatsoever cease to give or provide
the respective liens, security interests, rights, titles, interests, remedies,
powers or privileges intended to be created thereby; or

         E.   A default, other than the Existing Defaults, shall occur in the
performance of any material term, condition, covenant or agreement contained in
the Loan Documents, in this Agreement, or in connection with any other
obligation owing by Borrower to Bank; or

                                       -8-

<PAGE>

     F. Borrower shall do any of the following acts, or violate any other term
or provision of this Agreement: (i) apply for or consent to the appointment of a
receiver, trustee, custodian, intervenor or liquidator of all or a substantial
part of its assets; (ii) file a voluntary petition in bankruptcy court or admit
in writing that it is unable to pay its debts as they become due; (iii) make a
general assignment for the benefit of creditors; (iv) file a petition or answer
seeking reorganization or take advantage of any bankruptcy or insolvency laws;
(v) file an answer admitting any of the material allegations of, or consent to,
or default in answering a petition filed against it, in any bankruptcy,
reorganization or insolvency proceeding; or (vi) take any action for the purpose
of effecting any of the foregoing; or

     G. Any of the following acts or events occur: (i) an order for relief,
judgment or decree shall be entered by any court of competent jurisdiction or
other competent authority approving a petition seeking reorganization of
Borrower; (ii) an order shall be entered by any court of competent jurisdiction
or other competent authority appointing a receiver, custodian, trustee,
intervenor or liquidator for Borrower as to all or substantially all of its
assets, and such order, judgment or decree shall continue un-stayed and in
effect for a period of sixty (60) days; or (iii) an involuntary petition seeking
bankruptcy, reorganization or receivership shall be filed against Borrower which
is not dismissed within sixty (60) days of the filing thereof; or (iv) an event
of default under any of Borrower's obligations to the Bank; or

     H. Any change should occur which, in the opinion of Bank, has resulted or
could result in a Material Adverse Change.

     XII. Remedies.
          --------

     A. If an Event of Default shall occur under this Agreement, any other Loan
Document, or any other agreement referenced herein or executed in connection
herewith, Bank may exercise, at its election, and without notice, demand,
protest or presentment (which notice, demand, protest and presentment are
expressly waived) in addition to all rights and remedies granted to it in the
Loan Documents, any or all of the following (failure to specify any remedy
herein shall not limit Bank's remedies, nor be deemed to create a conflict or
contradiction with the Loan Documents):

          1. Bank may exercise all of its rights and remedies and may declare
     all amounts owed under the Loan Documents immediately due and payable;

          2. Bank may proceed to enforce the Loan Documents and this Agreement
     and exercise any or all of the rights and remedies afforded to Bank by the
     California Commercial Code, the California Civil Code, the California Code
     of Civil Procedure or otherwise possessed by Bank;

          3. Bank may, to the fullest extent permitted by law: (1) sell its
     Collateral or any interest therein at public or private sale for cash or
     upon credit and for immediate or future delivery and for such price and on
     such terms as Bank shall deem appropriate, and negotiate, endorse, assign,
     transfer and deliver to the purchaser or purchasers thereof (which may be
     Bank) the Collateral so sold, and each purchaser at any sale shall hold the
     property sold absolutely free from any claim or right on the part of
     Borrower (and Borrower hereby waives, to the extent permitted by law, all
     rights of redemption, stay and/or appraisal which Borrower now has or may
     at any time in the future have); and/or

                                       -9-

<PAGE>

      (2) obtain specific performance by Borrower of any covenant or undertaking
      of Borrower in the Loan Documents herein; and/or (3) without notice to
      Borrower, proceed by suit or suits at law or in equity to foreclose its
      security interest and sell its Collateral or any portion thereof pursuant
      to judgment or decree of a court, courts or referee having competent
      jurisdiction; and/or (4) without notice to Borrower, exercise any of its
      rights under, or foreclose its Collateral thereunder;

          4. Without regard to the adequacy of Bank's Collateral, or to the
      solvency of Borrower, Bank may institute legal proceedings for the
      appointment of a receiver or receivers with respect to any or all of its
      Collateral pending foreclosure hereunder or for the sale of any or all of
      its Collateral under the order of a court of competent jurisdiction or
      under other legal process;

          5. Either personally, or by means of a court-appointed receiver, Bank
      may enter onto the premises where its Collateral is located and take
      possession of all or any of its Collateral and exclude therefrom Borrower
      and all others claiming under Borrower, and perform any acts necessary or
      appropriate to care for, maintain, preserve and protect its Collateral. In
      the event Bank demands or attempts to take possession of its Collateral in
      the exercise of any rights hereunder, Borrower promises and agrees to turn
      over promptly and to deliver complete possession thereof to Bank;

          6. Without notice to or demand upon Borrower, Bank may make such
      payments and do such acts as Bank may deem necessary to protect its
      security interest in its Collateral including, without limitation, paying,
      purchasing, contesting or compromising any encumbrance, charge or lien
      which is prior to or superior to the security interests granted in the
      Loan Documents and, in exercising any such powers or authority, to pay all
      expenses incurred in connection therewith; and/or

          7. Enforce any of the rights and remedies available to it under the
      Loan Documents or this Agreement, or according to applicable law.

      B.  All rights and remedies granted to Bank hereunder are cumulative, and
Bank shall have the right to exercise any one or more of such rights and
remedies alternatively, successively or concurrently as Bank may, in its sole
and absolute discretion, deem advisable.

      XIII. Revival Clause; Solvency.
            ------------------------

      If the incurring of any debt or the payment of money or transfer of
property made to Bank by or on behalf of Borrower should for any reason
subsequently be declared to be "fraudulent" or "preferential" within the meaning
of any state or federal law relating to creditor's rights, including, without
limitation, fraudulent conveyances, preferences or otherwise voidable or
recoverable payments of money or transfers of property, in whole or in part, for
any reason (collectively, "Voidable Transfers") under the Bankruptcy Code or any
other federal or state law, and Bank is required to repay or restore any such
Voidable Transfer or the amount or any portion thereof, or upon the advice of
its in-house counsel or outside counsel is advised to do so, then, as to such
Voidable Transfer or the amount repaid or restored (including all reasonable
costs, expenses and attorneys' fees of Bank related thereto), the liability of
Borrower under the Credit Agreement and Loan Documents, and all of Bank's rights
and remedies under the Credit

                                      -10-

<PAGE>

Agreement and Loan Documents, shall automatically be revived, reinstated and
restored and shall exist as though such Voidable Transfer had never been made to
the extent of any harm to Bank.

         Borrower represents and warrants that the execution, delivery and
performance of this Agreement will not (i) render Borrower insolvent as that
term is defined below; (ii) leave Borrower with remaining assets which
constitute unreasonably small capital given the nature of Borrower's business;
or (iii) result in the incurrence of Debts (as defined below) beyond Borrower's
ability to pay them when and as they mature and become due and payable. For the
purposes of this paragraph, "Insolvent" means that the present fair salable
value of assets is less than the amount that will be required to pay the
probable liability on existing Debts as they become absolute and matured. For
the purposes of this paragraph, "Debts" includes any legal liability for
indebtedness, whether matured or unmatured, liquidated or unliquidated,
absolute, fixed or contingent. Borrower hereby acknowledges and warrants that it
has derived or expects to derive a financial or other benefit or advantage from
this Agreement.

         XIV. Notices.
              -------

         All notices required to or permitted to be given to Bank under this
Agreement shall be addressed as follows:

              To:               Thomas G. Kinzel
                                Vice President
                                Comerica Bank - California
                                9920 South La Cienega Boulevard, Suite 623
                                Inglewood, CA 90301
                                Fax No. (310) 338-6160

              Copy:             Pillsbury Winthrop LLP
                                101 West Broadway, Suite 1800
                                San Diego, California 92101
                                Attn: Daniel C. Minteer, Esq.
                                Fax No. (619) 236-1995

         All notices required to or permitted to be given to Borrower under this
Agreement shall be addressed as follows:

                                      -11-

<PAGE>

              To:           Mr. Paul A. Rosinack
                            President and Chief Executive Officer
                            Synbiotics Corporation
                            11011 Via Frontera
                            San Diego, CA 92127
                            Fax No.: (858) 451-5719

              Copy:         Brobeck, Phleger & Harrison LLP
                            12390 El Camino Real
                            San Diego, CA 92130
                            Attn: Hayden J. Trubitt, Esq.
                            Fax No.: (858) 720-2555

              Copy:         Mr. Christopher P. Hendy, Member
                            Redwood West Coast, LLC
                            9468 Montgomery Road
                            Cincinnati, OH 45242
                            Fax No.: (513) 984-8121

              Copy:         Keating, Muething & Klekamp PLL
                            1400 Provident Tower
                            One East Fourth Street
                            Cincinnati, OH 45202
                            Attn: Gary P. Kreider, Esq.
                            Fax No.: (513) 579-6457

         The above addresses may be changed effective upon receipt of a new
address. Any notice required herein or permitted to be given shall be in writing
and be personally served or sent by facsimile (upon confirmation of receipt) and
overnight United States mail and shall be deemed given when sent or, if mailed,
when deposited in the United States mail so long as it is properly addressed.

         XV.  Representations and Warranties. Borrower hereby represents and
              ------------------------------
warrants that:

         A.   Representations and Warranties. All Representations and Warranties
              ------------------------------
contained in the Credit Agreement are true and correct as of the date of this
Agreement. Except for Events of Default waived in this Agreement, no Event of
Default has occurred and/or is continuing.

         B.   Further Representations. No representation or warranty of Borrower
              -----------------------
contained in this Agreement or in any documents provided to Bank in connection
herewith (including any financial statements and/or financial information)
misstates any material fact or omits to state a material fact, the absence of
which makes such representation, warranty or statement misleading.

         XVI. Authority. Each party hereto represents and warrants to each other
              ---------
party that (i) it has authority to execute this Agreement; (ii) the execution,
delivery and performance of this Agreement does not require the consent or
approval of any person, entity, governmental body, trust, trustor or other
authority; (iii) this Agreement is a valid, binding and legal obligation of the
undersigned enforceable in accordance with its terms, and does not contravene or
conflict with any other agreement, indenture or undertaking to which any party
hereto is a party; and (iv) each

                                       -12-

<PAGE>

party hereto is the sole and lawful owner of all right, title, and interest in
and to every claim and other matter which the party purports to settle or
compromise herein.

     XVII.  Payment of Expenses. In the event any action (whether or not in a
            -------------------
court proceeding) shall be required to interpret, implement, modify, or enforce
the terms and provisions of this Agreement, or to declare rights under same, the
prevailing party in such action shall recover from the losing party all of its
fees and costs, including, but not limited to, the reasonable attorneys' fees
and costs (if applicable) of Bank's outside and in-house counsel.

     XVIII. Governing Law. This Agreement shall be construed and interpreted in
            -------------
accordance with and shall be governed by the laws of the state of California.
The parties also hereby agree to submit to the jurisdiction of the California
courts with respect to all matters relating to this Agreement.

     XIX.   Successors, Assigns. This Agreement shall be binding on and inure to
            -------------------
the benefit of all of the parties hereto, and upon the heirs, executors,
administrators, legal representatives, successors and assigns of the parties
hereto, and each of them. The terms and provisions of this Agreement are for the
exclusive benefit of Borrower and Bank, and may not be transferred, assigned,
pledged, set over or negotiated to any person or entity without the prior
express written consent of Bank. Notwithstanding any other provisions contained
herein, Bank may sell, transfer, negotiate, assign or grant participations in
all or a portion of its rights in any of the Loan Documents, in this Agreement,
to any person or entity without prior notice to Borrower, provided, however,
that any such assignee shall be bound by the terms and provisions of the Loan
Documents and this Agreement.

     XX.    Jury Trial Waiver
            -----------------

     BORROWER AND BANK EACH HEREBY WAIVE THEIR RESPECTIVE RIGHTS TO A JURY TRIAL
OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF ANY OF THE LOAN
DOCUMENTS OR ANY OF THE TRANSACTIONS CONTEMPLATED THEREIN, INCLUDING CONTRACT
CLAIMS, TORT CLAIMS, BREACH OF DUTY CLAIMS, AND ALL OTHER COMMON LAW OR
STATUTORY CLAIMS. EACH PARTY RECOGNIZES AND AGREES THAT THE FOREGOING WAIVER
CONSTITUTES A MATERIAL INDUCEMENT FOR IT TO ENTER INTO THIS AGREEMENT. EACH
PARTY REPRESENTS AND WARRANTS THAT IT HAS REVIEWED THIS WAIVER WITH ITS LEGAL
COUNSEL AND THAT IT KNOWINGLY AND VOLUNTARILY WAIVES ITS JURY TRIAL RIGHTS
FOLLOWING CONSULTATION WITH LEGAL COUNSEL.

     XXI.   Complete Agreement of Parties. This Agreement constitutes the entire
            -----------------------------
agreement between Bank and Borrower arising out of, related to or connected with
the subject matter of this Agreement. Any supplements, modifications, waivers or
terminations of this Agreement shall not be binding unless executed in writing
by the parties to be bound thereby. No waiver of any provision of this Agreement
shall constitute a waiver of any other provisions of this Agreement (whether
similar or not), nor shall such waiver constitute a continuing waiver unless
otherwise expressly so provided. However, this Agreement does not alter or amend
any provision of any of the Loan Documents except to the extent of the
provisions expressly set forth herein.

                                      -13-

<PAGE>

     XXII.  Execution In Counterparts. This Agreement may be executed in any
            -------------------------
number of counterparts each of which, when so executed and delivered, shall be
deemed an original, and all of which together shall constitute but one and the
same agreement.

     XXIII. Contradictory Terms/Severability. In the event that any term or
            --------------------------------
provision of this Agreement contradicts any term or provision of any other
document, instrument or agreement between the parties including, but not limited
to, any of the Loan Documents, the terms of this Agreement shall control. If any
provision of this Agreement shall be invalid, illegal or otherwise
unenforceable, such provision shall be severable from all other provisions of
this Agreement, and the validity, legality and enforceability of the remaining
provisions of this Agreement shall not be adversely affected or impaired, and
shall thereby remain in full force and effect.

     XXIV.  Headings. All headings contained herein are for convenience purposes
            --------
only, and shall not be considered when interpreting this Agreement.

     XXV.   Continuing Cooperation. The parties hereto shall cooperate with each
            ----------------------
other in carrying out the terms and intent of this Agreement, and shall execute
such other documents, instruments and agreements as are reasonably required to
effectuate the terms and intent of this Agreement.

     XXVI.  Consultation With Counsel. Each party hereto acknowledges that (i)
            -------------------------
it has been represented by counsel of its own choice at each stage in the
negotiation of this Agreement; (ii) it has relied on such counsel's advice
throughout all of the negotiations which preceded the execution of this
Agreement, and in connection with the preparation and execution of this
Agreement; (iii) such counsel has read this Agreement; (iv) such counsel has
advised such party concerning the validity and effectiveness of this Agreement,
and the transactions to be consummated in accordance therewith and/or each party
has had the opportunity to consult with counsel and has voluntarily waived doing
so; and (v) each party hereto is freely and voluntarily entering into this
Agreement.

AGREED AND ACCEPTED:
-------------------

COMERICA BANK - CALIFORNIA,
a California banking corporation

By:   /s/ Thomas G. Kinzel                           Dated: January 25, 2002
      --------------------
      Thomas G. Kinzel
      Vice President

SYNBIOTICS CORPORATION,
a California corporation

By:   /s/ Paul A. Rosinack                           Dated: January 25, 2002
      --------------------
      Paul A. Rosinack
      President

                                       -14-

<PAGE>

                                    EXHIBIT A
                                    ---------

     Incorporated herein by reference to Exhibit 4.4.4 to this Current Report on
Form 8-K.

                                      -15-

<PAGE>

                                    EXHIBIT B
                                    ---------

                                (Form of Consent)


                       Consent of Redwood West Coast, LLC
                       ----------------------------------

         REDWOOD WEST COAST, LLC ("Redwood") hereby consents to the execution
and delivery of the foregoing Third Amendment to Credit Agreement and Loan
Documents and Waiver of Defaults ("Agreement") dated as of January 25, 2002 by
SYNBIOTICS CORPORATION ("Borrower") to and between COMERICA BANK - CALIFORNIA,
successor in interest to Imperial Bank, a California banking corporation,
("Bank"). All capitalized terms not defined herein shall have the meaning
attributed to them in the Agreement.

         Redwood acknowledges the amount and validity of Borrower's loan
obligations to Bank as described in Sections I.A. and I.B. of the Agreement, and
the existence, validity, perfection and priority of bank's liens in the
Collateral as described in Section I.A.3. of the Agreement. Redwood acknowledges
that Borrower is in default under the Loan Documents, subject to Bank's
agreement to waive defaults upon the satisfaction or waiver of Conditions
Precedent, as more fully specified in the Agreement.

         Redwood agrees that is rights to receive compensation for services,
dividends and/or any other payment or consideration from Borrower are subject to
the limitations set forth in Sections 5.08 of the Credit Agreement, as modified
by the Agreement, and Sections V.A. and V.C. of the Agreement, and Redwood's
agreements with the Borrower are deemed modified accordingly.

REDWOOD WEST COAST, LLC
a Delaware limited liability company

By:   __________________________________       Dated: January 25, 2002
      _____________________
      Its: ________________

                                      -16-