AMENDMENT TO THE AGREEMENT AND PLAN OF MERGER

Exhibit 10.1

AMENDMENT

TO THE

AGREEMENT AND PLAN OF MERGER

Amendment, dated as of January 7, 2009 (this “ Amendment ”), to the Agreement and Plan of Merger (the “ Agreement ”), dated as of January 5, 2009, by and among Endo Pharmaceuticals Holdings Inc., a Delaware corporation (“ Parent ”), BTB Purchaser Inc., a Delaware corporation and a direct, wholly-owned Subsidiary of Parent (“ Merger Sub ”), and Indevus Pharmaceuticals, Inc., a Delaware corporation (the “ Company ”).

W I T N E S S E T H :

WHEREAS, in accordance with Section 8.3 of the Agreement, Parent, Merger Sub and the Company wish to amend the terms of the Agreement as provided in Section I below;

WHEREAS, unless otherwise defined herein, capitalized terms used but not defined herein shall have the meanings assigned to them in the Agreement;

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

SECTION I

AMENDMENT

The first sentence of Section 1.1(a)(i) of the Agreement is hereby deleted and re