Posted on behalf of Beth Mole.

A highly anticipated new drug for treating hepatitis C has sailed through its first phase III clinical trials, according to two papers published today in the New England Journal of Medicine.

Sofosbuvir, a new antiviral developed by Gilead Sciences of Foster City, California, is one of several drugs in the pipeline that could replace hepatitis C treatments that incorporate the immune-boosting drug interferon, which can cause harsh side effects including depression, anaemia and severe flu-like symptoms. Up to 170 million people worldwide are infected with blood-borne hepatitis C virus (HCV), including as many as 4 million people in the United States. Long-term exposure to the virus can cause chronic liver disease and cancer. Current therapies that combine the antiviral drug ribavirin and interferon cure up to 75% of those treated, but take as long as a year to do so.

Facing a lengthy drug regimen that can produce debilitating side effects, many patients — who may not develop liver damage for years — delay or refuse treatment. And with the promise of better drugs on the way, some doctors approve waiting.

The two papers published today suggest that the wait for improved hepatitis C treatment regimens may be coming to an end. Researchers led by Ira Jacobson of Weill-Cornell Medical College in New York report that a combination of sofosbuvir and ribavirin cured up to 78% of trial participants infected with two types of HCV — genotypes 2 and 3 — in as few as three months, without the need for interferon. That result is similar to outcomes from earlier phase II trials. Another team, led by Eric Lawitz of the Texas Liver Institute at the University of Texas Health Science Center in San Antonio, showed that a combination of sofosbuvir, ribavirin and interferon cured up to 90% of patients with HCV genotype 1, the most common variety.

“The results are certainly a step forward,” says David Thomas, a hepatitis C expert at the Johns Hopkins Center for Global Health in Baltimore, Maryland. But he adds that most physicians will be more excited to see results from an ongoing trial that is testing the effectiveness of treating HCV genotype 1 patients with sofosbuvir without interferon.

In the meantime, Gilead is seeking approval to market sofosbuvir in the United States. The company submitted an application for new drug approval to the US Food and Drug Administration (FDA) on 8 April.

Thomas says this first set of phase III trials puts sofosbuvir well on the path towards FDA approval. “This starts the clock,” he says, adding that he has already scheduled one of his HCV genotype 1 patients to come in for an interferon-free treatment regimen in December.