Pharmasset has commenced dosing in an exploratory study of PSI-7977, a nucleotide analog polymerase inhibitor, for the treatment of chronic hepatitis C (HCV).

The trial will evaluate PSI-7977 400mg QD in combination with ribavirin (RBV), with 0, 4, 8, or 12 weeks of pegylated interferon alfa 2a (Peg-IFN) in treatment-naive patients infected with HCV genotype 2 or 3.

Pharmasset anticipates to enroll approximately 40 patients infected with HCV genotype 2 or 3 who have not previously been treated.

The primary endpoint of the trial will be the assessment of safety and tolerability of PSI-7977 400mg QD and RBV for 12 weeks, administered with or without pegylated interferon (Peg-IFN) in treatment naive patients with HCV genotypes 2 or 3.

Pharmasset chief medical officer Michelle Berrey said that based on the encouraging efficacy, safety and resistance data from the Phase 2a trial with PSI-7977 in combination with pegylated interferon and ribavirin, they initiated a study to explore shorter durations of interferon, including an interferon-free regimen in treatment naïve patients with HCV genotype 2 or 3.

"We believe that PSI-7977's high barrier to resistance and the lack of a significant effect of IL28B genotype in the Phase 2a trial provide us an opportunity with PSI-7977 to explore shorter durations of interferon, and potentially even removing it from the treatment regimen altogether," Berrey said.