Exhibit 10.45

AMENDMENT NO. 1 TO FACILITY AGREEMENT

This AMENDMENT NO. 1 TO FACILITY AGREEMENT (this “Amendment No. 1”), dated as of
October 22, 2008, is made by and among ZymoGenetics, Inc. and Deerfield Private
Design Fund, L.P. and Deerfield Private Design International, L.P. (together the
“Original Deerfield Lenders”) and Deerfield ZG Corporation (“DZG”).

W I T N E S S E T H

WHEREAS, the parties hereto other than DZG have entered into the Facility
Agreement, dated June 26, 2008 (the “FA”); and

WHEREAS, the parties to this Amendment No. 1 desire to amend the FA to add
Deerfield ZG as a party thereto;

NOW, THEREFORE, the parties hereto agree as follows:

1. Deerfield ZG shall become a party to the FA and the definition of “Lenders”
shall include the Original Deerfield Lenders and DZG; provided, however, that
for the purposes of Sections 2.11 and 5.4, the definition of “Lenders” shall not
include DZG.

2. For the purpose of Section 3.3, DZG shall not make the representations and
warranties set forth in paragraphs (a) through (g) but shall make the
representations and warranties set forth in paragraphs (h) through (k) mutatis
mutandis (e.g., in paragraph (h) DZG is a corporation).

3. The last sentence of Section 2.2 shall be deleted and replaced with the
following:

“For the purpose of the first paragraph of the Notes, each Disbursement shall be
allocated 61.7% to Deerfield Private Design International, L.P. and 38.3% to
Deerfield Private Design Fund, L.P.”

4. Except as amended hereby, the FA shall remain in full force and effect.

Signature page follows.

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IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1 to be
signed as of the date first above written.

 

BORROWER:

ZYMOGENETICS, INC.

     

LENDER:

DEERFIELD PRIVATE DESIGN FUND, L.P.

By:

 

/s/ James A. Johnson

      By:  

/s/ James Flynn

Name:

  James A. Johnson       Name:   James Flynn

Title:

 

Executive Vice President and

Chief Financial Officer

      Title:   General Partner

 

LENDER:

DEERFIELD PRIVATE DESIGN

INTERNATIONAL, L.P.

       

By:

 

/s/ James Flynn

       

Name:

  James Flynn        

Title:

  General Partner        

 

LENDER:

DEERFIELD ZG CORPORATION

       

By:

 

/s/ James Flynn

        Name:   James Flynn        

Title:

  General Partner