The FDA’s Antiviral Drugs Advisory Committee unanimously voted on Thursday that a second protease inhibitor, telaprevir (Vertex), is safe and effective for treating patients with hepatitis C virus (HCV) genotype 1.

On Wednesday, the panel voted in favor of approving boceprevir (Merck) for the same indication. If approved, the two agents will be the first HCV therapies available that directly target the virus.

The current standard therapy, pegylated interferon with ribavirin, functions to boost patients’ immune systems — but only about half of those treated with the combo achieve a sustained viral response.

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But clinical trial data presented to the panel on Thursday indicate that telaprevir increased response rates to the 70% to 90% range among patients who had never before been treated.

These rates were lower in patients that had not previously responded to HCV treatment, but still higher than rates in control groups that underwent a second round of therapy with conventional treatment.

Furthermore, patients that were prescribed telaprevir had much lower relapse rates — 5% vs. 26% in previously untreated patients and 10% vs. 57% in those who had already received HCV therapy.

The most common adverse events were rash and pruritus, which occurred in more than half of patients, and three patients in the telaprevir group experienced Stevens-Johnson Syndrome, a severe life-threatening skin reaction.

Once telaprevir becomes widely available, clinician should warn patients about the risks for adverse skin reactions and closely monitor them for rash development, the committee advised.

The FDA will decide whether to approve both telaprevir and boceprevir in May.