Penwest Pharmaceutical Confirms Patent and Trademark Office Action on Oxymorphone Patent Application

DANBURY, Conn., March 15 /PRNewswire-FirstCall/ -- Penwest Pharmaceuticals Co. today confirmed that the U.S. Patent and Trademark Office (PTO) has posted on its website an indication that a final rejection of Penwest's patent application claiming the sustained release formulations of Oxymorphone will be mailed. This is one of several patent applications that Penwest is currently prosecuting related to Opana(R) ER (oxymorphone HCl) extended-release tablets CII, a product the Company developed with Endo Pharmceuticals. Opana ER is indicated for the treatment of moderate-to-severe pain in patients requiring continuous, around-the-clock opioid treatment for an extended period of time. It is currently marketed by Endo.

A "final rejection" notice from the PTO is a part of the examining process by the PTO when the patent examiner does not allow all the pending claims. It does not end the Company's ability to pursue these claims. The Company has several options to respond to the final rejection, including appealing the final rejection by the examiner to the Board of Patent Appeals at the U.S. Patent and Trademark Office.

Jennifer L. Good, President and Chief Executive Officer of Penwest, said "We are disappointed with this action by the U.S. Patent and Trademark Office. Once we receive the Office Action from the Patent Office, we will respond as quickly as possible and continue to work with the Patent Office to move this application forward. In the meantime, Penwest and Endo continue to prosecute eight other patent applications related to Opana ER, some of which we believe could receive an Office Action later this year."

Penwest Pharmaceuticals

Penwest is a specialty pharmaceutical company dedicated to bringing to the marketplace innovative products that help improve the lives of patients. The Company's goal is to identify, develop and commercialize prescription products that address unmet medical needs, primarily for diseases of the nervous system. At the core of this strategy, Penwest applies drug delivery technologies, including its own proprietary technologies, to new and existing compounds to enhance their therapeutic profiles. The launch by Endo Pharmaceuticals in mid-2006 of Opana(R) ER (oxymorphone hydrochloride extended-release tablets) formulated with the Company's TIMERx(R) extended release delivery technology demonstrates the execution of this strategy and the value of the Company's TIMERx(R) technology. The Company is currently applying its expertise to a pipeline of potential products that are in various stages of development. The Company intends to commercialize these products independently or through third party alliances.

The matters discussed herein contain forward-looking statements that involve risks and uncertainties, which may cause Penwest's actual results in future periods to be materially different from any future performance suggested herein. For this purpose, any statements contained herein that are not statements of historical fact may be deemed to be forward-looking statements. Without limiting the foregoing, the words, "believes," "anticipates," "plans," "expects," "intends," "potential," and similar expressions are intended to identify forward-looking statements. Important factors that could cause results to differ materially include: risks relating to the commercial success of our products; regulatory risks relating to drugs in development, including the timing and outcome of regulatory action; uncertainty of success of collaborations; the timing of clinical trials and whether the results of clinical trials will warrant further clinical trials or warrant submission of an application for regulatory approval of, or the regulatory approval of, the product that is the subject of the trial; actual and potential competition; the need for capital; and other risks as set forth under the caption Risk Factors in Penwest's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on November 9, 2006, which risk factors are incorporated herein by reference.

The forward-looking statements contained in this press release speak only as of the date of the statement made. Penwest disclaims any intention or obligation to update any forward-looking statements.

Contacts: Investors: Media: Ben Palleiko/Diane D'Alessandro Caroline Gentile/Laura Walters (203) 796-3706 Kekst and Company (877) 736-9378 (212) 521-4800

Penwest Pharmaceuticals Co.

CONTACT: Investors - Ben Palleiko or Diane D'Alessandro, +1-203-796-3706or 1-877-736-9378; Caroline Gentile or Laura Walters, both of Kekst andCompany, +1-212-521-4800