Pharmasset, Inc. has completed patient enrolment of the ongoing multiple ascending dose study of R7128 for the treatment of hepatitis C virus (HCV). R7128, a nucleoside polymerase inhibitor of HCV, is currently being evaluated in a phase 1 clinical trial as part of Pharmasset's collaboration with Roche.

The primary objective of the multiple ascending dose study is to assess the safety, tolerability and pharmacokinetics of R7128 after once-daily or twice- daily dosing for 14 days in up to 40 patients chronically infected with HCV genotype 1 who have previously failed interferon therapy. The secondary objective is to assess antiviral efficacy by measuring the change in HCV RNA in these patients.

Pharmasset expects to release preliminary 14-day safety and efficacy treatment data from the multiple ascending dose study in September 2007. Results for the entire phase 1 single ascending and multiple ascending dose study are expected to be presented at various scientific conferences throughout the remainder of 2007. As recently announced, Roche has initiated long-term chronic toxicology studies in support of the potential advancement of R7128 into Phase 2 clinical trials.

R7128 is a polymerase inhibitor being developed for the treatment of chronic hepatitis C. R7128 is a pro-drug of PSI-6130, which demonstrated potency in preclinical studies. PSI-6130 is a pyrimidine nucleoside analog inhibitor of HCV RNA polymerase, an enzyme that is necessary for hepatitis C viral replication. Results from an oral single ascending dose study in 24 healthy male volunteers showed that PSI-6130 was generally well tolerated with no serious adverse events in doses up to 3000 mg.

The phase 1 clinical trial is a multiple centre, observer-blinded, randomized and placebo-controlled study to investigate the pharmacokinetics, pharmacodynamics, safety, tolerability and food effect of R7128 in healthy volunteers and in patients chronically infected with HCV genotype 1.