In the United States, the current standard of care for the treatment of HCV is a combination of pegylated interferon and a nucleoside analog named ribavirin. According to the World Health Organization, however, this combination of drugs achieves sustained virologic responses (SVRs)—a viral cure characterized by an undetectable viral load six months after discontinuing treatment—in only 30 to 50 percent receiving both pegylated interferon and ribavirin. In addition, these therapies have serious side effects that include fatigue, bone marrow suppression, anemia and neuropsychiatric effects.

As a result of the limited benefits and serious side effects of existing therapies, Pharmasset is one of several pharmaceutical and biotechnology companies developing new agents active against HCV, to be used in combination with pegylated interferon and ribavirin or as alternatives to both currently approved agents.

Two agents being developed by Pharmasset are PSI-938 and PSI-7977, two nucleotide analogs designed to prevent the virus from taking hold in the cellular machinery of liver cells (hepatocytes). PSI-7977 is currently in Phase II development, whereas PSI-938 is still in Phase I clinical trials.

One study, to be reported in a late-breaker presentation at EASL, suggests that they work remarkably well together, potentially without the use of either pegylated interferon or ribavirin.  According to, the combination of both Pharmasset drugs saw HCV viral loads reduced to below the level of detection in 15 of 15 treated patients after just 14 days of treatment. “This is the best such early-stage data released on an oral drug for hepatitis C,” reports. “And the PSI-938 and PSI-7977 one-two punch eliminates the need for interferon, which is linked to a number of side effects among patients.”

Full data from the study, which have been embargoed until they are presented in Berlin, will be reported here.