Enrollment for ongoing phase 2b trial of RG7128 announced

Pharmasset, Inc. (Nasdaq: VRUS) announced today that the enrollment of Cohort 2, led by its partner Roche (SWX: ROG.VX; RO.S, OTCQX: RHHBY), will continue for the remaining 300 genotype 1 and 4 patients in the ongoing phase 2b trial of RG7128, a first-in-class nucleoside analog polymerase inhibitor for the treatment of chronic hepatitis C virus (HCV) infection. The decision was reached after a scheduled review by an independent Data Monitoring Committee (DMC) of all available safety data from the first cohort of approximately 100 patients completing 8 or 12 weeks of RG7128 or matching placebo in combination with pegylated interferon and ribavirin.

The DMC reviewed any potential drug discontinuations, incidence and details of adverse events, and selected laboratory assessments. No safety events in the DMC review were considered significantly different from those expected from HCV patients taking pegylated interferon and ribavirin treatment. The committee expressed no safety concerns that would preclude enrollment of the remaining 300 patients in the ongoing phase 2b study in the HCV positive genotype 1 and 4 population, and have not recommended modification of dose or duration of any RG7128 dosing regimens. Enrollment of these patients pre-screened for this Cohort in the fourth quarter 2009 has begun and is expected to be complete by the end of the first quarter of 2010.

"We welcome Roche's decision to open enrollment of Cohort 2 for the remaining 300 patients in the phase 2b trial," stated Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "We are encouraged by the safety profile of RG7128 to date, which, when coupled with the higher barrier to resistance offered by nucleoside and nucleotide analog inhibitors has the potential to improve SVR rates over the current standard of care."

Additional RG7128 Studies

Pharmasset's development partner, Roche, plans to initiate a number of additional, longer duration phase 2b trials with RG7128 in the first half of 2010. An additional study in patients infected with HCV genotypes 2 and 3 is being planned to initiate later in 2010.