Pharmasset has received fast track designation from the FDA for PSI-938 for the treatment of chronic hepatitis C virus (HCV) infection. This designation was primarily due to the need for improved HCV treatments in tolerability, safety and efficacy over existing standard of care for both treatment-naïve and treatment-experienced patients.

In March 2011, Pharmasset presented data from the NUCLEAR study showing that PSI-938 has potent antiviral activity and is generally safe and well tolerated in both monotherapy and in combination with PSI-7977, Pharmasset’s lead nucleotide analog.  The NUCLEAR study was conducted in treatment-naïve patients with genotype 1 HCV who were treated with PSI-938 or a combination of PSI-938 and PSI-7977 for 14 days. In the combination arms, 92% of patients achieved HCV RNA <15Units/mL, the limit of detection. Pharmasset plans to initiate the QUANTUM combination trial with PSI-938 and PSI-7977 in the third quarter of 2011.

PSI-938 is an oral guanosine nucleotide analog polymerase inhibitor of HCV.

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