Pharmasset initiates PSI-7977 Phase 3 program for HCV

Pharmasset, Inc. (Nasdaq: VRUS) today announced the initiation of a Phase 3 program with the hepatitis C virus (HCV) nucleotide analog, PSI-7977. This pivotal program will evaluate a 12-week, all-oral, interferon-free regimen of PSI-7977 and ribavirin in patients with HCV, independent of viral genotype or their ability to take interferon therapy.

"After recent discussions with Health Authorities, we are excited to be initiating the first of a series of pivotal studies to explore an interferon-free regimen of PSI-7977 in broad populations of individuals with HCV," said Michael Rogers, Ph.D., Pharmasset's Chief Development Officer.

The first trial, FISSION, will enroll approximately 500 treatment-naive patients with HCV genotype 2 or 3, and will evaluate the safety and efficacy of a 12-week interferon-free regimen of PSI-7977 and ribavirin compared to 24 weeks of pegylated interferon and ribavirin. The primary endpoint of the study is sustained virologic response 12 weeks after the completion of treatment (SVR12).

Pharmasset plans to initiate a second 12-week duration, interferon-free Phase 3 trial, POSITRON, in early 2012. This trial will enroll approximately 225 patients with HCV genotype 2 or 3 who cannot take interferon.

In mid-2012, Pharmasset intends to initiate a third 12-week duration, interferon-free Phase 3 trial, NEUTRINO. This trial will enroll patients who cannot take interferon, and will include patients with HCV regardless of viral genotype, including those with HCV genotype 1. The final study design will be based on emerging data from ELECTRON and from PSI-7977 plus RBV-containing arms in the ongoing QUANTUM study.

"Based on encouraging results to date, we have selected an IFN-free regimen of PSI-7977/RBV for our registrational program," said Michelle Berrey, MD, MPH, Pharmasset's Chief Medical Officer. "We continue to believe that interferon remains the greatest impediment to care for a majority of the millions of individuals living with HCV.  PSI-7977 has demonstrated high cure rates, without viral resistance, and across HCV genotypes; we hope to confirm these benefits in these registrational studies."