Pharmasset Inc., of Princeton, N.J., said screening has begun in a Phase IIb study of PSI-7977, a nucleotide analogue polymerase inhibitor for the treatment of chronic hepatitis C (HCV). The 300-patient trial will evaluate PSI-7977 400 mg QD with pegylated interferon and ribavirin in patients with HCV genotype 1, 4, 5 or 6 who have not been treated previously. The primary endpoint is the safety and tolerability of PSI-7977 in combination with peginterferon and ribavirin over 12 or 24 weeks.