AMENDMENT NO. 1
Dated as of March 5, 2009
Dated as of June 29, 2007
THIS AMENDMENT NO. 1 (“ Amendment ”) is made as of March 5, 2009, and effective as of
December 31, 2008, by and among Biogen Idec Inc., a Delaware corporation (the “ Borrower ”), the financial
institutions listed on the signature pages hereof and Bank of America, N.A., as Administrative Agent (the “
Administrative Agent ”), under that certain Credit Agreement dated as of June 29, 2007 by and among the
Borrower, the Lenders and the Administrative Agent (as amended, supplemented or otherwise modified from
time to time, the “ Credit Agreement ”). Capitalized terms used herein and not otherwise defined herein shall have
the respective meanings given to them in the Credit Agreement.
WHEREAS, the Borrower has requested that certain modifications be made to the Credit Agreement;
WHEREAS, the Borrower, the Lenders party hereto and the Administrative Agent have agreed to amend
the Credit Agreement on the terms and conditions set forth herein;
NOW, THEREFORE, in consideration of the premises set forth above, the terms and conditions
contained herein, and other good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrower, the Lenders party hereto and the Administrative Agent hereby agree to the
following amendments to the Credit Agreement.
1. Amendments to Credit Agreement . Subject to the satisfaction of the conditions precedent set forth in
Section 2 below, the Credit Agreement is hereby amended as follows:
(a) Section 2.03(i) of the Credit Agreement is amended to delete the phrase “for the account of each
Lender” appearing in the first sentence thereof and to replace such phrase with the phrase “for the account of
each Lender (other than any Defaulting Lender)”.
(b) Section 2.06 of the Credit Agreement is amended by adding “except as explicitly set forth