Pharmasset initiates Phase IIb clinical trial of PSI-7977 for chronic hepatitis C

Interim data for trial is expected in the first half of 2011

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PRINCETON, N.J.—Pharmasset Inc., which trades on Nasdaq under the ticker symbol VRUS, has announced that dosing has begun in a Phase IIb study of PSI-7977, a nucleotide analog polymerase inhibitor for the treatment of chronic hepatitis C (HCV). The trial will evaluate PSI-7977 at 200 milligrams once daily and 400 milligrams once daily in combination with pegylated interferon alfa 2a and ribavirin, which is the current standard of care in patients with HCV genotype 1 who have not been treated previously.

"We look for the Phase IIb to further support the efficacy, safety and resistance profile of PSI-7977 over 12 weeks, and to confirm a dose for continued development," says Dr. Michelle Berrey, Pharmasset's chief medical officer. "Given the potent antiviral activity observed in the Phase IIa study and in vitro evidence for pan-genotype activity, we have also decided to include an exploratory, open label arm of patients with HCV genotype 2 and 3 who will receive a 12-week treatment regimen of PSI-7977 in combination with pegylated interferon and ribavirin. If successful, this shorter treatment regimen would be a first step toward defining a new treatment option for these patients."

The trial is anticipated to enroll approximately 125 patients in the United States who are infected with HCV genotype 1 who have not been treated previously. The primary endpoint of the trial will be the assessment of safety and tolerability of PSI-7977, in combination with standard of care over 12 weeks with response-guided therapy allowing discontinuation of the standard of care at week 24.

In addition, approximately 25 treatment-naive patients with HCV genotype 2 or 3 will be enrolled in a fourth, open-label arm, receiving PSI-7977 400 milligrams once a day with standard of care for 12 weeks, with no standard of care follow-up.

Pharmasset anticipates reporting interim data from this trial in the first half of 2011.

The news was enough for Canaccord Genuity, the global capital markets group of Canaccord Financial Inc., to reiterate a "buy" rating for the company.

"We think this bodes well for VRUS since PSI-7977 is a wholly owned, once-daily (QD) pill and could become a component of future direct acting antiviral (DAA) combination therapies," wrote Adam Cutler and Dr. Manisha Narasimhan of Canaccord Genuity in an investment note about Pharmasset right after the announcement.

Pharmasset is a clinical-stage pharmaceutical company committed to discovering, developing, and commercializing novel drugs to treat viral infections. Pharmasset's primary focus is on the development of oral therapeutics for the treatment of HCV and, secondarily, on the development of Racivir for the treatment of human immunodeficiency virus (HIV).

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