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                                                                  EXHIBIT 10.6
                           AMENDMENT NUMBER ONE TO THE
                      AGREEMENT AND PLAN OF REORGANIZATION


         This Amendment Number One (this "Amendment") to the Agreement and
Plan of Reorganization dated as of June 30, 1997 (the "Agreement") among
Triangle Pharmaceuticals, Inc. ("Triangle"), Project Z Corporation ("Project
Z") and Avid Corporation ("Avid"), is made as of this 28th day of February,
1999, by and among Triangle, Avid and Forrest H. Anthony, Alan G. Walton and
Marcia T. Bates (the "Securityholder Agent"), on behalf of and as
attorney-in-fact for all of the stockholders, optionholders and
warrantholders of Avid immediately prior to the merger of Project Z with and
into Avid (the "Former Avid Stockholders"). Capitalized terms used herein
which are not defined herein shall have the definitions ascribed to them in
the Agreement.

                                    RECITALS

         A. Triangle, Project Z and Avid entered into the Agreement, pursuant
to which Project Z merged with and into Avid on August 28, 1997, and Avid
became a wholly-owned subsidiary of Triangle.

         B. Triangle, Avid and the Securityholder Agent, on behalf of and as
attorney-in-fact for the Former Avid Stockholders, desire to extend the
eighteen (18) month period set forth in Section 1.6(b)(ii)(B) of the
Agreement after which, if Triangle has not Initiated a Definitive Clinical
Trial with the Lead Compound or elected in writing to continue the
development of the Lead Compound, the Securityholder Agent will have the
option to either exercise the Lead Compound Option and to amend certain other
provisions of the Agreement as set forth herein.

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

         1.       AMENDMENTS TO AGREEMENT.

                  1.1      SECTION 1.6(B).  The first paragraph of Section
1.6(b) is hereby amended and restated in its entirety as follows:

                           "(b) STOCK CONSIDERATION. The "Stock Consideration"
         shall be the number of shares of Parent Common Stock equal to the sum
         of (x) the First Payment (as defined in Section 1.6(b)(i) below) plus
         (y) the Second Payment (as defined in Amendment Number One to this
         Agreement) plus (z) the Milestone Payments (as defined in Section
         1.6(b)(ii) below)."

                  1.2 SECTION 1.6(B)(II)(A). Section 1.6(b)(ii)(A) of the
Agreement is hereby amended and restated in its entirety as follows:

                           "(A) In the event that Parent, in its sole
         discretion, (x) Initiates (as defined in Section 1.6(b)(iii) below) a
         Definitive Clinical Trial (as defined in Section 1.6(b)(iii) below)
         with the Lead Compound (as defined in Section 1.6(b)(iii) below), or
         (y) notifies the Securityholder Agent (as defined in Section


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         7.2(g) below) in a writing that specifically references this Section
         1.6(b)(ii)(A) of its election to continue the development of the Lead
         Compound even if Parent has not Initiated a Definitive Clinical Trial
         with the Lead Compound, Parent shall within seventy-five (75) days
         thereafter make available to the Exchange Agent (as defined in Section
         1.10(a) below) for distribution pursuant to Section 1.10, 1,500,000
         shares of Parent Common Stock."

                  1.3 SECTION 1.6(B)(II)(B). Section 1.6(b)(ii)(B) of the
Agreement is hereby amended and restated in its entirety as follows:

                           "(B) If neither of the conditions described in
         Section 1.6(b)(ii)(A) above is satisfied on or prior to thirty (30)
         months after the Closing Date and the Securityholder Agent elects not
         to exercise the Lead Compound Option (as defined in Section 5.17
         below) within the thirty (30) day period set forth in Section 5.17
         below, Parent shall within seventy-five (75) days thereafter make
         available to the Exchange Agent for distribution pursuant to Section
         1.10, 100,000 shares of Parent Common Stock."

                  1.4 SECTION 1.7(B)(III). Section 1.7(b)(iii) of the Agreement
is hereby amended and restated in its entirety as follows:

                           "(iii) REVALUATION OF DESIGNATED ASSETS.
         Notwithstanding any prior distribution of the Designated Assets, as of
         the date on which all unexercised Assumed Options and Assumed Warrants
         expire (the "Revaluation Date"), the Designated Assets shall be
         redistributed among the Former Company Stockholders in accordance with
         Section 1.7(b)(ii) based on the valuation of such Designated Assets as
         of the Revaluation Date. Solely for purposes of the redistribution of
         the Designated Assets as of the Revaluation Date contemplated by this
         Section 1.7(b)(iii), the shares of Parent Common Stock included in
         such Designated Assets shall be valued at the average of the closing
         prices of Parent Common Stock on the Nasdaq National Market for the
         five (5) consecutive trading days ending five (5) trading days prior
         to the Revaluation Date. No revaluation or redistribution of any of
         the Designated Assets shall occur with respect to the Stock
         Consideration, if any, distributed by Parent after the Revaluation
         Date. In no event, however, shall the aggregate value of the Merger
         Consideration distributed to the holders of Company Preferred Stock be
         less than the aggregate value of the Merger Consideration distributed
         to the holders of the Company Common Stock and the holders of Assumed
         Options and Assumed Warrants."

                  1.5 SECTION 1.8(C)(I)(A). Section 1.8(c)(i)(A) of the
Agreement is hereby amended and restated in its entirety as follows:

                           "(A) At the Effective Time, each Assumed Option
          shall be, in connection with the Merger, assumed by Parent. Each
          Assumed Option so assumed by Parent under this Agreement shall be
          amended prior to the Effective Time to provide that from and after
          the Effective Time such Assumed Option (1) may be exercised through a
          cashless exercise procedure (to the extent that the Assumed Option
          does not already permit the holder thereof to do so) and may be


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          exercised notwithstanding the failure of the holder thereof to enter
          or remain in the employ of Parent or the Company following the
          Merger, (2) may not be exercised at any time prior to the earlier of
          (a) thirty (30) months after the Closing Date and (b) the date, if
          any, of the written notice from the Securityholder Agent addressed to
          the last known domicile address of the holder of such Assumed Option
          informing such holder that one of the conditions described in Section
          1.6(b)(ii)(A) above has been satisfied (the earlier of such dates
          being the "Option Exercise Date"), (3) may not be exercised at any
          time after 5:00 p.m. eastern standard time on the date that is
          forty-five (45) days after the Option Exercise Date, and (4)
          represents only the right to receive upon exercise the portion of the
          Merger Consideration issuable to such holder pursuant to Section 1.7
          above. Except as so amended, each Assumed Option shall continue to
          have, and be subject to, the same terms and conditions set forth in
          the Option Plan under which it was issued and/or as provided in the
          respective option agreements governing such Assumed Option
          immediately prior to the Effective Time. Parent shall reserve from
          the Cash Distribution the amount, if any, that the holders of the
          Assumed Options would have received had all of the Assumed Options
          and all of the Assumed Warrants been exercised in full immediately
          prior to the Effective Time (assuming that the exercise price was
          paid in cash). The portion of the Cash Distribution reserved by
          Parent for issuance upon exercise of the Assumed Options is referred
          to as the "Assumed Option Amount." "

                  1.6 SECTION 1.8(D)(I)(A). Section 1.8(d)(i)(A) of the
Agreement is hereby amended and restated in its entirety as follows:

                           "(A) At the Effective Time, each Assumed Warrant
         shall be, in connection with the Merger, assumed by Parent. Each
         Assumed Warrant so assumed by Parent under this Agreement shall be
         amended prior to the Effective Time to provide that from and after the
         Effective Time such Warrant (1) may be exercised through a cashless
         exercise procedure (to the extent that the Assumed Warrant does not
         already permit the holder thereof to do so), (2) may not be exercised
         at any time prior to the earlier of (a) thirty (30) months after the
         Closing Date and (b) the date, if any, of the written notice from the
         Securityholder Agent addressed to the last known domicile address of
         the holder of such Assumed Warrant informing such holder that one of
         the conditions described in Section 1.6(b)(ii)(A) above has been
         satisfied (the earlier of such dates being the "Warrant Exercise
         Date"), (3) may not be exercised at any time after 5:00 p.m. eastern
         standard time on the date that is forty-five (45) days after the
         Warrant Exercise Date, and (4) represents only the right to receive
         upon exercise the portion of the Merger Consideration issuable to such
         holder pursuant to Section 1.7 above. Except as so amended (and as the
         warrants issued by the Company to Dominion Ventures, Inc. may be
         further amended as contemplated by Section 6.3(s) below prior to the
         Effective Time), each Assumed Warrant shall continue to have, and be
         subject to, the same terms and conditions as provided in the
         respective Assumed Warrant agreement immediately prior to the
         Effective Time. Parent shall reserve from the Cash Distribution the
         amount, if any, that the holders of the Assumed Warrants would have
         received had all of the Assumed Warrants and all


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         of the Assumed Options been exercised in full immediately prior to the
         Effective Time (assuming that the exercise price was paid in cash).
         The portion of the Cash Distribution reserved by Parent for issuance
         upon exercise of the Assumed Warrants is referred to as the "Assumed
         Warrant Amount." "

                  1.7 SECTION 5.17. The first paragraph of Section 5.17 of the
Agreement is hereby amended and restated in its entirety as follows:

                           "5.17 OPTION TO OBTAIN RIGHTS TO LEAD COMPOUND. In
         the event that neither of the conditions described in Section
         1.6(b)(ii)(A) is satisfied on or prior to the date that is thirty (30)
         months after the Closing Date, the Securityholder Agent shall have the
         option ("Lead Compound Option"), subject to the conditions and on the
         terms described below, to acquire on behalf of each holder of any
         Company Capital Stock outstanding immediately prior to the Effective
         Time and each holder of an Assumed Option or an Assumed Warrant that
         is timely and properly exercised after the Closing (together, the
         "Former Company Stockholders") pursuant to the Technology Transfer
         Agreement in the form attached hereto as EXHIBIT 5.17 (the "Technology
         Transfer Agreement"): (i) all of Parent's and the Company's rights in
         the Lead Compound, in all improvements solely and exclusively of, and
         enhancements solely and exclusively to, the Lead Compound (the "Lead
         Compound Improvements") and in all documents and data created solely
         and exclusively in connection with the development of the Lead
         Compound (the "Lead Compound Information") (and in both the case of
         Lead Compound Improvements and Lead Compound Information, not in any
         way related to any of the other compounds, technologies or assets of
         Parent or the Company), and (ii) one copy of all documents that
         contain any data regarding clinical trials of the Lead Compound in
         combination with other drugs or drug candidates, redacted to exclude
         therefrom any other information contained therein (together with the
         Lead Compound Information, the "Lead Compound Documents"). In the
         event the Securityholder Agent delivers written notice to Parent of
         his or her election to exercise the Lead Compound Option within thirty
         (30) calendar days after the date of the Parent Notice (as defined in
         Section 5.17(a) below), Parent shall thereafter, subject to and in
         compliance with good medical and clinical trial practices, promptly
         and permanently cease, and shall cause the Company to cease, all
         development and use of the Lead Compound, the Lead Compound
         Improvements and the Lead Compound Documents (collectively, the "Lead
         Compound Rights")."

                  1.8 SECTION 7.2(B)(I). Section 7.2(b)(i) of the Agreement is
hereby amended and restated in its entirety as follows:

                           "(i) In the event that neither of the conditions
         described in Section 1.6(b)(ii)(A) is satisfied on or prior to the
         date that is eighteen (18) months after the Closing Date, Parent and
         the Securityholder Agent shall deliver written notice to the Escrow
         Agent certifying that neither of the conditions has been satisfied.
         The Escrow Agent shall within seventy-five (75) days thereafter
         deliver to the stockholders of the Company the portion of the Escrow
         Fund, if any, in excess of 200,000 shares of Parent


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         Common Stock, not including the Second Payment. Deliveries of Escrow
         Amounts to the stockholders of the Company pursuant to this Section
         7.2(b)(i) shall be made in accordance with Section 1.7(b)(ii) based on
         their interest in such Escrow Amounts as of February 28, 1999. Parent
         shall reserve from such distribution the amount, if any, that the
         holders of the Assumed Options and the Assumed Warrants would have
         received had all of the Assumed Options and all of the Assumed
         Warrants been exercised in full on February 28, 1999. Solely for
         purposes of the distribution pursuant to this Section 7.2(b)(i) the
         shares of Parent Common Stock included in such distribution shall be
         valued at the average of the closing prices of Parent Common Stock on
         the Nasdaq National Market for the five (5) consecutive trading days
         ending February 28, 1999, and not at the value as of the Revaluation
         Date. The Escrow Agent shall not be obligated to deliver any Escrow
         Amounts to the stockholders of the Company pursuant to Section
         7.2(b)(i) unless and until the Securityholder Agent shall have
         delivered an Agent Certificate to Parent and the Escrow Agent with
         respect to such Escrow Amounts as required by this Section 7.2(b)(i)."

                  1.9 SECTION 7.2(B)(II). Section 7.2(b)(ii) of the Agreement
is hereby amended and restated in its entirety as follows:

                           "(ii) As soon as all claims specified in any
         Officer's Certificate delivered to the Escrow Agent prior to
         termination of the Escrow Period have been resolved and after the
         termination of the Escrow Period, the Escrow Agent shall deliver to
         the stockholders of the Company the remaining portion of the Escrow
         Fund, not including the Second Payment, not required to satisfy such
         claims. Deliveries of Escrow Amounts to the stockholders of the
         Company pursuant to this Section 7.2(b)(ii) shall be made in
         accordance with Section 1.7(b)(ii) based on their interest in such
         Escrow Amounts as of August 31, 1999. Parent shall reserve from such
         distribution the amount, if any, that the holders of the Assumed
         Options and the Assumed Warrants would have received had all of the
         Assumed Options and all of the Assumed Warrants been exercised in full
         on August 31, 1999. Solely for purposes of the distribution pursuant
         to this Section 7.2(b)(ii) the shares of Parent Common Stock included
         in such distribution shall be valued at the average of the closing
         prices of Parent Common Stock on the Nasdaq National Market for the
         five (5) consecutive trading days ending August 31, 1999, and not at
         the value as of the Revaluation Date. The Escrow Agent shall not be
         obligated to deliver any Escrow Amounts to the stockholders of the
         Company pursuant to Section 7.2(b)(ii) unless and until the
         Securityholder Agent shall have delivered an Agent Certificate to
         Parent and the Escrow Agent with respect to such Escrow Amounts as
         required by this Section 7.2(b)(ii)."

         2.       SECOND PAYMENT.

                  Triangle shall, on or before May 14, 1999, or as soon
thereafter as is reasonably practicable, deliver 100,000 shares of Triangle
Common Stock (the "Second Payment") to the Escrow Agent. The certificate for
the Second Payment shall be issued as of April 1, 1999, shall be deposited in
the Escrow Fund and shall be held by the Escrow Agent for each of the Former
Avid Stockholders in proportion to the aggregate number of shares of Parent
Common Stock which such holder would otherwise be entitled to receive from
the aggregate of the First


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 Payment and the Second Payment pursuant to Section 1.7 of the Agreement by
virtue of such holder's ownership of outstanding shares of Company Capital
Stock immediately prior to the Effective Time, and assuming for the purposes
of such allocation that the holders of all Assumed Options and the holders of
all Assumed Warrants were the holders of the number of shares of the Company
Common Stock that would have been issued had all of the Assumed Options and
all of the Assumed Warrants been exercised in full immediately prior to the
Effective Time (assuming that the exercise price was paid in cash). The
Second Payment shall not be subject to claims against the Escrow Fund by
Triangle for Losses pursuant to Section 7.2 of the Agreement, except for
Losses, if any, identified in Subsection 7.2(a)(iv) of the Agreement. Subject
to the receipt of an Agent Certificate, in form acceptable to Triangle,
pursuant to Section 1.7(d)(i) of the Agreement with respect to the
distribution of the Second Payment, the Second Payment shall be distributed
from the Escrow Account within seventy-five (75) days after the expiration of
the thirty (30) month period set forth in Section 1.6(b)(ii)(B) of the
Agreement. Triangle shall be entitled to rely without investigation on the
accuracy of the information set forth in such Agent Certificate.

         3.       SECURITYHOLDER AGENT'S EXPENSES.

                  Triangle shall pay the reasonable fees and expenses of
legal counsel to the Securityholder Agent incurred in connection with the
drafting and review of this Amendment and the transactions contemplated
hereby, subject to verification of fees by Triangle.

         4.       EFFECT OF AMENDMENT.

                  Except as amended and set forth above, the Agreement shall
continue in full force and effect. In the event of any conflict between the
terms of the Agreement and the terms of this Amendment, the terms of this
Amendment shall govern and control.

         5.       FURTHER ASSURANCES.

                  The parties agree to execute such further instruments,
agreement and documents and to take such further action as may reasonably be
necessary to carry out the intent of this Amendment.

         6.       COUNTERPARTS.

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

         7.       SEVERABILITY.

                  If one or more provisions of this Amendment are held to be
unenforceable under applicable law, such provision shall be excluded from
this Amendment and the balance of the Amendment shall be interpreted as if
such provision were so excluded and shall be enforceable in accordance with
its terms.


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         8.       GOVERNING LAW.

                  This Amendment shall be governed by and construed under the
laws of the State of Delaware regardless of the laws that might otherwise
govern under applicable principles of conflicts of laws thereof.

                [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]


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         This Amendment is hereby executed as of the date first above written.

TRIANGLE:                                 TRIANGLE PHARMACEUTICALS, INC., a
                                          Delaware corporation


                                          By:
                                             ---------------------------------
                                             M. Nixon Ellis, President and
                                             Chief Operating Officer

AVID:                                     AVID CORPORATION, a Pennsylvania
                                          corporation


                                          By:
                                             ---------------------------------
                                              M. Nixon Ellis, President

SECURITYHOLDER AGENT:

                                          ------------------------------------
                                              Forrest H. Anthony


                                          ------------------------------------
                                              Alan G. Walton


                                          ------------------------------------
                                              Marcia T. Bates






                   [SIGNATURE PAGE TO AMENDMENT NUMBER ONE TO
                    THE AGREEMENT AND PLAN OF REORGANIZATION]