Back HCV Treatment Pharmasset Halts Testing of HCV Polymerase Inhibitor PSI-938 Due to Liver Problems

Pharmasset Halts Testing of HCV Polymerase Inhibitor PSI-938 Due to Liver Problems


Pharmasset announced in December that it would change the design of its ongoing QUANTUM trial to discontinue treatment with its hepatitis C virus (HCV) nucleotide polymerase inhibitor PSI-938, after routine safety monitoring revealed liver function abnormalities.

The trial was testing PSI-938 in combination with the complementary polymerase inhibitor PSI-7977 and ribavirin. Evaluation will continue for the latter 2 drugs, which have not been linked to liver problems. A study recently presented at the American Association for the Study of Liver Disease (AASLD) Liver Meeting showed that 12 weeks of PSI-7977 plus ribavirin produced 100% sustained response in previously untreated people with HCV genotypes 2 or 3.

Below is an edited excerpt from a Pharmasset press release describing  the changes to the trial.

Pharmasset Announces Intent to Amend QUANTUM Trial

Princeton, N.J. -- December 16, 2011-- Pharmasset, Inc. (Nasdaq: VRUS) announced today that the company will amend the design of the QUANTUM Phase 2b trial of the guanine nucleotide analog PSI-938 and discontinue all treatment arms with a regimen containing PSI-938. There are 235 individuals with hepatitis C virus (HCV) in the study who are receiving treatment with PSI-938 alone or in combination with PSI-7977 or PSI-7977 and ribavirin.

During routine safety monitoring, the company detected laboratory abnormalities associated with liver function in subjects receiving PSI-938 300 mg once daily. These laboratory abnormalities have not been observed in patients receiving PSI-7977 and ribavirin in the QUANTUM study or in other trials evaluating PSI-7977. Both the 12 and 24-week PSI-7977 and ribavirin arms will continue unchanged, data from which will support NEUTRINO, an interferon free, 12-week Phase 3 study of PSI-7977 and ribavirin in patients with HCV genotype 1 (GT-1).

The subject of today's announcement does not trigger the "key product event" clause set forth in section 4.1(t) of the Agreement and Plan of Merger entered into by Pharmasset and Gilead Sciences, Inc. on November 21, 2011 and does not alter either party's rights and obligations under the terms of the agreement. Pharmasset anticipates that the transaction announced on November 21, 2011 will conclude in the first quarter of 2012.

About Pharmasset

Pharmasset is a clinical-stage pharmaceutical company committed to discovering, developing, and commercializing novel drugs to treat viral infections. Pharmasset's primary focus is the development of oral therapeutics for the treatment of hepatitis C virus (HCV) infection. Our research and development efforts are focused on nucleoside/tide analogs, a class of compounds which act as alternative substrates for the viral polymerase, thus inhibiting viral replication. We currently have two clinical-stage product candidates advancing in trials in various populations. Our pyrimidine, PSI-7977, an unpartnered uracil nucleotide analog, is currently being studied in an interferon-free, Phase 3 program (FISSION and POSITRON) and in five Phase 2b trials in subjects with all HCV genotypes. Mericitabine (RG7128) continues in multiple Phase 2b trials and one interferon-free trial being conducted through a strategic collaboration with Roche.



Pharmasset, Inc. Pharmasset Announces Intent to Amend QUANTUM Trial. Press release. December 16, 2011.