PRINCETON, N.J., May 26, 2011 /PRNewswire/ — Pharmasset, Inc.
(Nasdaq:
VRUS) announced today the initiation of a Phase 2a trial
investigating the combination of Pharmasset’s PSI-7977, a
nucleotide polymerase inhibitor, and BMS-790052, Bristol-Myers
Squibb Company’s (NYSE:
BMY) NS5A replication complex inhibitor, for the treatment of
chronic hepatitis C (HCV).  This trial is the result of a
clinical collaboration agreement between Pharmasset and
Bristol-Myers Squibb announced in January 2011.

“We are happy to announce the initiation of this important
combination trial,” stated William Symonds, Pharmasset’s Senior
Vice President of Clinical Pharmacology and Translational Medicine.
“Recent data from Bristol-Myers Squibb’s combination study
demonstrated that individuals with HCV can be cured without the
traditional interferon and ribavirin, but only if two potent DAAs
are used and drug resistance is avoided. We believe Pharmasset’s
nucleotide analogs have demonstrated potent antiviral activity and
a high barrier to resistance and therefore have the potential to be
the future backbone of interferon-free treatment.”

About the Trial

This Phase 2a trial is planned to enroll approximately 84
patients with chronic HCV genotypes 1, 2 or 3 who have not been
treated previously. The primary endpoint of the trial is sustained
virologic response (SVR). The trial will be conducted in the U.S.
Subjects will be randomized equally across each of the following
arms:

• PSI-7977 400mg QD for 7 days, then add BMS-790052 60mg QD for
  further 23 weeks in genotype 1 subjects;
• PSI-7977 400mg QD for 7 days, then add BMS-790052 60mg QD for
  further 23 weeks in genotype 2 or 3 subjects;
• PSI-7977 400mg QD and BMS-790052 60mg QD for 24 weeks in
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