Exhibit 10.1

February 26, 2013

Board of Directors of Optimer Pharmaceuticals, Inc.,

101 Hudson Street, Suite 3501,

Jersey City, NJ 07302.

Fellow Members of the Board,

I defer to your decision to appoint Hank McKinnell as Chief Executive Officer and, subject to your acceptance, resign as both an officer and director of Optimer Pharmaceuticals, Inc.

This letter confirms the understanding that my resignation will be treated for purposes of my employment arrangements with Optimer as a termination without cause.  In addition, I recognize that events occurring during my tenure at Optimer are under heightened scrutiny.  I therefore confirm that I will repay any amounts and benefits I receive as a result of such treatment of my resignation in the event that it is finally determined by a court that I engaged in any act for which I would not be entitled to indemnification under Section 8.1 of Optimer’s by-laws.

		Very truly yours,
		/s/ Pedro Lichtinger
		Pedro Lichtinger
Accepted and Agreed:
Optimer Pharmaceuticals, Inc.
By:	/s/ Anthony E. Altig
Anthony E. Altig
Chairman, Compensation and Governance/
Nominating Committee