Pharmasset Reports Positive Preliminary Antiviral Data For PSI-7851

Pharmasset has reported positive preliminary results from phase I clinical trial of PSI-7851, for the treatment of hepatitis C (HCV). PSI-7851 is a second generation nucleotide polymerase inhibitor of HCV.

Pharmasset initiated a phase 1 multiple ascending dose study with PSI-7851 in June, 2009. The trial was conducted at two US centers, as a blinded, randomized, and placebo-controlled study, in 30 patients chronically infected with HCV genotype 1.

The primary objective was to assess the safety, tolerability, and pharmacokinetics of PSI-7851 after once-daily (QD) dosing for 3 days. The secondary objective was to assess antiviral activity by measuring the change in HCV RNA. Patients were randomized to receive either PSI-7851 (eight patients per cohort) or placebo (two patients per cohort). Three dose cohorts of PSI-7851 (50mg QD, 100mg QD, 200mg QD) were evaluated.

PSI-7851 demonstrated potent antiviral activity with a mean HCV RNA decrease of -0.49 log(10) IU/mL, -0.61 log(10) IU/mL and -1.01 log(10) IU/mL, in patients receiving 50mg QD, 100mg QD, and 200mg QD, respectively.

Michelle Berrey, chief medical officer of Pharmasset, said: We are very encouraged by the preliminary efficacy and safety data with PSI-7851, our second generation nucleotide analog. The data from these first three cohorts demonstrate that we have achieved our goal of identifying a nucleotide analog with good efficacy that can be administered once daily at a low milligram dose. Given these characteristics and the potential benefits of nucleotide analogs over other classes of HCV direct acting antivirals, we continue to believe that PSI-7851 could become a key component of any future combination treatment regimen for HCV.