Corporate Overview

We are a clinical-stage pharmaceutical company committed to discovering, developing and commercializing novel drugs to treat viral infections. Our primary focus is on the development of oral therapeutics for the treatment of hepatitis B virus (“HBV”), hepatitis C virus (“HCV”) and human immunodeficiency virus (“HIV”). We currently have three product candidates:

• Clevudine, for the treatment of chronic HBV infection, is enrolling Phase 3 registration clinical trials;
• R7128, a pro-drug of PSI-6130 for the treatment of HCV, is in a 4-week Phase 1 clinical trial through a collaboration with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (collectively, “Roche”); and
• Racivir, for the treatment of HIV, which has completed a Phase 2 clinical trial.

Additionally, we are continuing to identify the best path forward for the development of dexelvucitabine, or DFC, for the treatment of HIV following the completion of a Phase 2b clinical trial. The Company has also nominated a proprietary HCV lead development candidate, PSI-7851, that is being evaluated for potential clinical development.

Our research and development efforts focus on a class of compounds known as nucleoside analogs, which act to inhibit the enzymes required for viral replication. We are applying our expertise in nucleoside chemistry to the discovery and development of additional antiviral therapeutics for HCV and HIV.

Our Strategy

Our primary objective is to become a leader in discovering, developing and commercializing novel antiviral therapeutics that provide a competitive advantage and address unmet medical needs. Our primary focus is on the development of oral therapeutics for the treatment of HBV, HCV and HIV. To achieve this goal, we are pursuing the following strategies:

• Focus on developing our current clinical-stage product candidates and advancing them toward marketing approval.
• Maintain a broad pipeline of potential product candidates to diversify commercial opportunities and reduce our dependence on any one product candidate’s clinical or commercial success.
• Leverage our core competency in nucleoside chemistry for research innovation and the discovery of additional product candidates.
• Commercialize our products ourselves or through collaborations, where appropriate, to optimize economic returns while managing financial risk.