Under the terms of one of two types of purchase agreements, Optimer will sell 2.79 million newly issued shares of its common stock at a purchase price of $10 per share. In the other purchase agreement Optimer will sell 457,666 newly issued units at a purchase price of $10.925 per unit, with each unit consisting of one share of common stock and one warrant to purchase 0.20 of a share of common stock.

The warrants are exercisable six months after the date of issuance at $10.93 per share and will expire five years from the date of issuance.

The closing of this offering is expected to take place on March 9, 2009. Proceeds from the transaction will be used in the further development of Optimer's ongoing programs, as well as for other general corporate purposes.

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