AMENDMENT TO RIGHTS AGREEMENT


     THIS AMENDMENT NO. 1 TO RIGHTS AGREEMENT (the
“Amendment”) is made as of the 20th day of August, 2009, by and
between AVIGEN, INC., a Delaware corporation (the
“Company”), and AMERICAN STOCK TRANSFER & TRUST
CO. LLC (the “Rights Agent”). 

     WHEREAS, the Company is entering into an Agreement and Plan of Merger
(as the same may be amended from time to time, the “Merger Agreement”), among
the Company, MediciNova, Inc., a Delaware corporation (“Parent”), and Absolute
Merger, Inc., a Delaware corporation and a direct wholly-owned subsidiary of
Parent (“Merger Sub”), pursuant to which Merger Sub will merge with and into the
Company upon the terms and subject to the conditions set forth in the Merger
Agreement (the “Merger”) and the Company will continue as the surviving
corporation of the Merger in accordance with the General Corporation Law of the
State of Delaware;

     WHEREAS, the Company and the Rights Agent are parties to that certain
Rights Agreement, dated as of November 21, 2008 (the “Rights
Agreement”);

     WHEREAS, Section 27 of the Rights Agreement permits the Company to
amend the Rights Agreement on the terms set forth in this
Amendment; 

     WHEREAS, the Company desires to amend the Rights Agreement in
connection with the execution and delivery of the Merger Agreement; and


     WHEREAS, the Board of Directors of the Company has determined that it
is in the best interests of the Company and its stockholders to modify the terms
of the Rights Agreement to exempt the Merger, the Merger Agreement and the
transactions contemplated thereby from the application of the Rights Agreement
and has approved this Amendment and authorized its appropriate officers to
execute and deliver the same to the Rights Agent. 

     NOW, THEREFORE, in accordance with the procedures for amendment of the Rights
Agreement set forth in Section 27 thereof, and in consideration of the foregoing
and the mutual agreements herein set forth, the parties hereby agree as follows:


     1. Capitalized terms that are not otherwise defined herein shall have the
meanings ascribed to them in the Rights Agreement.

     2. The definition
of “Acquiring Person” set forth in Section 1(a) of the Rights Agreement is amended and supplemented by adding the following
sentence to the end of that section:

     Notwithstanding anything in this Agreement to the contrary, no
Person shall be or become an Acquiring Person by reason of, and the term
Acquiring Person shall not include any Person by reason of, (i) the approval,
execution and delivery of the Agreement and Plan of Merger, dated as of August
20, 2009, by and among MediciNova, Inc., a Delaware corporation (“Parent”),
Absolute Merger, Inc., a Delaware corporation and a direct wholly-owned
subsidiary of Parent (“Merger Sub”), and the Company
(such Agreement and Plan of Merger, as the same may be amended from time to
time, is referred to in this Agreement as the “Merger Agreement”), (ii) the
merger of Merger Sub with and into the Company pursuant to, and on the terms and
subject to the conditions set forth in, the Merger Agreement (such merger is
referred to in this Agreement as the “Merger”), (iii) the consummation of any
other transaction contemplated by the Merger Agreement, or (iv) the announcement
of the Merger Agreement, the Merger or any other transaction contemplated by the
Merger Agreement.

1. 




     
3.
The definition of “Interested
Stockholder” set forth in Section 1(j) of the Rights Agreement is amended and supplemented by adding the following sentence to
the end of that section: 

      Notwithstanding anything in this Agreement to the contrary,
no Person shall be or become an Interested Stockholder by reason of, and the
term Interested Stockholder shall not include any Person by reason of, (i) the
approval, execution and delivery of the Merger Agreement, (ii) the Merger, (iii)
the consummation of any other transaction contemplated by the Merger Agreement,
or (iv) the announcement of the Merger Agreement, the Merger or any other
transaction contemplated by the Merger Agreement.

     
4.
The definition of “Shares Acquisition
Date” in Section l(o) of the Rights Agreement is
hereby amended and supplemented by adding the following sentence to the end of
that section: 

     Notwithstanding anything in this Agreement to the contrary, no
Shares Acquisition Date shall be deemed to have occurred by reason of (i) the
approval, execution and delivery of the Merger Agreement, (ii) the Merger, (iii)
the consummation of any other transaction contemplated by the Merger Agreement,
or (iv) the announcement of the Merger Agreement, the Merger or any other
transaction contemplated by the Merger Agreement.

     5. Section 3(a) of the Rights Agreement is hereby amended and supplemented
by adding the following sentence to the end of that section: 

     Notwithstanding anything in this Agreement to the contrary, no
Distribution Date shall be deemed to have occurred by reason of (i) the
approval, execution and delivery of the Merger Agreement, (ii) the Merger, (iii)
the consummation of any other transaction contemplated by the Merger Agreement,
or (iv) the announcement of the Merger Agreement, the Merger or any other
transaction contemplated by the Merger Agreement.

     6. Section 7(a) is amended by deleting the word “or” before Section
7(a)(iii) and by adding the following clause at the end of Section 7(a):


     , or (iv) the moment in time immediately prior to the Merger
Effective Time (as such term is defined in the Merger Agreement).

2. 




     7. Section 11(a)(ii) of the Rights Agreement is hereby amended and
supplemented by adding the following sentence to the end of that
section:

     Notwithstanding anything else set forth in this Agreement, no event
requiring an adjustment under this Section 11(a) shall be deemed to have
occurred by reason of (i) the approval, execution and delivery of the Merger
Agreement, (ii) the Merger, (iii) the consummation of any other transaction
contemplated by the Merger Agreement, or (iv) the announcement of the Merger
Agreement, the Merger or any other transaction contemplated by the Merger
Agreement.

     8. Sections 13(a) of the Rights Agreement is hereby amended and supplemented
by adding the following sentence to the end of that section:

     Notwithstanding anything in this Agreement to the contrary, none of the
events described in clauses (x) through (z) of the first sentence of Section
13(a) shall be deemed to have occurred as a result of (i) the approval,
execution and delivery of the Merger Agreement, (ii) the Merger, (iii) the
consummation of any other transaction contemplated by the Merger Agreement, or
(iv) the announcement of the Merger Agreement, the Merger or any other
transaction contemplated by the Merger Agreement.

     9. The first phrase of Section 13(c) of the Rights Agreement is hereby
amended to read in its entirety as follows, with the remaining portion of
Section 13(c) being unchanged and remaining in full force and effect:

     The Company
shall not consummate any such consolidation, merger (other than any such
transaction contemplated by the Merger Agreement, including the Merger), sale or
transfer unless the Principal Party shall have a sufficient number of authorized
Common Shares that have not been issued or reserved for issuance to permit the
exercise in full of the Rights in accordance with this Section 13 and unless
prior thereto the Company and each Principal Party and each other Person who may
become a Principal Party as a result of such consolidation, merger, sale or
transfer shall have (i) executed and delivered to the Rights Agent a
supplemental agreement providing for the terms set forth in paragraphs (a) and
(b) of this Section 13 and (ii) prepared, filed and had declared and remain
effective a registration statement under the Act on the appropriate form with
respect to the Rights and the securities exercisable upon exercise of the
Rights, and the Company shall have furnished to the Rights Agent a certificate
setting forth the number of shares of Common Stock of such issuer which may be
purchased upon the exercise of each Right after the consummation of such
consolidation, merger, sale or transfer and further providing that, as soon as
practicable after the date of any consolidation, merger, sale or transfer of
assets mentioned in paragraph (a) of this Section 13, the Principal Party at its
own expense will: 

3. 




     10. Section 13(d)(i) of the Rights Agreement is hereby amended to read in its
entirety as follows:

     (i) consolidate with (other than by any transaction
contemplated by the Merger Agreement, including the Merger),

     11. Section 13(d)(ii) of the Rights Agreement is hereby amended to read in
its entirety as follows:

     (ii) merge with or into (other than by any transaction
contemplated by the Merger Agreement, including the Merger),

     12. Section 30 of the Rights Agreement is hereby amended and supplemented by
adding the following sentence to the end of that section:

     Nothing in this Agreement shall be construed to give any
holder of Rights or any other Person any legal or equitable rights, remedies or
claims under this Agreement by virtue of (i) the approval, execution and
delivery of the Merger Agreement, (ii) the Merger, (iii) the consummation of any
other transaction contemplated by the Merger Agreement, or (iv) the announcement
of the Merger Agreement, the Merger or any other transaction contemplated by the
Merger Agreement.

     13. The Rights Agreement, as amended by this Amendment, shall remain in full
force and effect in accordance with its terms. To the extent there is a conflict
between the terms and provisions of the Rights Agreement and this Amendment, the
terms and provisions of this Amendment shall govern for purposes of the subject
matter of this Amendment only. 

     14. All of the covenants and provisions of this Amendment by or for the
benefit of the Company or the Rights Agent shall bind and inure to the benefit
of their respective successors and assigns hereunder. 

     15. Nothing in this Amendment shall be construed to give to any person or
corporation other than the Company, Parent, Merger Sub, the Rights Agent and the
registered holders of the Right Certificates (and, prior to the Distribution
Date, the Common Shares) any legal or equitable right, remedy or claim under
this Amendment; but this Amendment shall be for the sole and exclusive benefit
of the Company, Parent, Merger Sub, the Rights Agent and the registered holders
of the Right Certificates (and, prior to the Distribution Date, the Common
Shares). 

     16. If any term, provision, covenant or restriction of this Amendment is held
by a court of competent jurisdiction or other authority to be invalid, void or
unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this Amendment shall remain in full force and effect and shall
in no way be affected, impaired or invalidated. 

     17. This Amendment shall be deemed to be a contract made under the laws of
the State of Delaware and for all purposes shall be governed by and construed in
accordance with the laws of such State applicable to contracts to be made and
performed entirely within such State. 

     18. This Amendment may be executed in any number of counterparts and each of
such counterparts shall for all purposes be deemed to be an original, and all
such counterparts shall together constitute but one and the same instrument.


4. 




     IN WITNESS
WHEREOF, the parties herein
have caused this Amendment to be duly executed and attested, all as of the date
and year first above written. 


	 	AVIGEN,
      INC.  	 
		 	  	
			 	
		By: 	/s/ Andrew Sauter  	
			Name:  	Andrew Sauter  	
			Title:  	CEO & CFO  	
			  	
			 	
			   	
		AMERICAN STOCK TRANSFER & TRUST CO. LLC  	
			  	
			 	
		By: 	/s/ Herbert J. Lemmer  	
			Name:  	Herbert J. Lemmer  	
			Title:  	Vice President  	



5.