Final SVR results from Pharmasset's PSI-7977 phase 2b study in HCV

Pharmasset, Inc. (Nasdaq: VRUS) announced today the final sustained virologic response (SVR) results from its phase 2b PROTON study with PSI-7977 dosed once daily in combination with peginterferon alfa 2a and ribavirin (Peg-IFN/RBV) in subjects with hepatitis C virus (HCV) genotype 2 or 3 who have not been treated previously. Twenty four out of twenty four subjects (100%) who completed treatment achieved an SVR, defined as HCV RNA below the limit of detection (<15 IU/ml) 24 weeks after the completion of treatment. No subject exhibited breakthrough on treatment or relapse after treatment.

Twenty five treatment-naive subjects with HCV genotype 2 or 3 were enrolled in an open label arm of the PROTON trial, receiving PSI-7977 400mg QD with Peg-IFN/RBV for 12 weeks, with no Peg-IFN/RBV follow-up. At the European Association for the Study of the Liver (EASL) in April 2011, Dr J. Lalezari presented interim results from this arm showing that 24 out of 24 subjects achieved an SVR12, defined as HCV RNA below the limit of detection (<15 IU/ml) 12 weeks after the completion of treatment. The combination was generally safe and well tolerated with one subject discontinuing treatment after day 1 and was lost to follow up. Overall PSI-7977 with Peg-IFN/RBV demonstrated potent viral suppression in subjects with HCV genotype 2 or 3 over 12 weeks of treatment.

Pharmasset anticipates reporting the SVR12 results from the PROTON trial in genotype 1 HCV subjects in the second half of 2011.