Pharmasset initiates dosing for additional cohorts in Phase I hepatitis trial

R7128 is being developed through the company’s collaboration with Roche. The purpose of this four-week study is to evaluate the safety, tolerability, pharmacokinetics and antiviral activity of R7128 in the clinically-relevant setting of combination therapy for chronic hepatitis C virus (HCV)infection. The previously planned cohort three will continue dose-exploration with administration of R7128 1000mg twice-daily (BID) in treatment-naive patients with HCV genotype 1.

Cohort four will evaluate R7128 1500mg BID administered in combination with Pegasys plus Copegus in treatment-experienced patients with genotypes two or three who did not achieve a sustained virologic response (SVR) with previous interferon-based therapy.

There will be 25 patients in each dose cohort with 20 patients randomized to receive R7128 and five patients randomized to receive placebo. After completing four weeks of the triple combination regimen and a follow-up period of four weeks of Pegasys plus Copegus, patients will receive an additional 16 to 40 weeks of open-label dosing of Pegasys plus Copegus under a separate protocol to complete the standard of care regimen for each genotype. Preliminary safety and antiviral activity data from the four-week combination treatment period are anticipated during the third quarter of 2008.