Pharmasset Inc., announces that the United States Patent and Trademark Office has issued US patent 7,964,580 (the '580 patent) titled “Nucleoside Phosphoramidate Prodrugs”. This patent generally relates to the composition of matter of PSI-7977 and its diastereomeric mixture for the treatment of Hepatitis C Virus (HCV). PSI-7977, a uracil nucleotide analogue polymerase inhibitor of HCV, is being studied in multiple phase 2 trials.

“Today's announcement is a credit to our in-house research team in discovering new HCV product candidates,” stated Schaefer Price, Pharmasset's president and chief executive officer. “As the '580 patent is not due to expire until 2029, not including any patent term extension, it should become an important part of a growing portfolio of issued patents covering PSI-7977.”

PSI-7977, one of two diastereomers comprising PSI-7851, is a prodrug of a uracil nucleotide analogue polymerase inhibitor we are developing for the treatment of chronic HCV infection. PSI-7977 has completed a 28 day phase II a trial in combination with peg-interferon and ribavirin (Peg-IFN/RBV) and is currently being tested in four phase II b studies: the Proton trial in combination with peg-IFN/RBV in HCV genotype 1, 2 or 3 patients; the Atomic trial with peg-IFN/RBV in HCV genotypes 1,4,5,6; the Electron trial, an interferon sparing /interferon free study in HCV genotypes 1,2 and 3 and a study with Bristol-Myers Squibb's NS5a inhibitor, BMS-790052, as part of an interferon free regimen. Pharmasset also anticipates initiating its own interferon free trial with PSI-7977 and PSI-938, a guanine nucleotide polymerase inhibitor in the third calendar quarter 2011.

Pharmasset is a clinical-stage pharmaceutical company committed to discovering, developing, and commercializing novel drugs to treat viral infections. It's primary focus is the development of oral therapeutics for the treatment of Hepatitis C Virus (HCV) infection.