Merck & Co’s once-daily, single pill, fixed-combination hepatitis C drug Zepatier has been cleared by the US Food and Drug Administration for patients with genotype 1 and 4 infections.

The approval of Zepatier (elbasvir/grazoprevir) was based on clinical data showing that the overall sustained virologic response (SVR) ranged from 94-97 percent in genotype 1-infected subjects and from 97-100 percent in genotype 4-infected subjects across trials for the approved treatment regimens.

Clinical data also show that the therapy cured the vast majority of hepatitis C patients who also had compensated liver cirrhosis, a traditionally difficult-to-treat population.

The most common side effects of Zepatier without ribavirin were found to be fatigue, headache and nausea, while the most common linked with the drug plus ribavirin were anaemia and headache.

Zepatier does, however, carries a warning alerting patients and healthcare providers that elevations of liver enzymes to greater than five times the upper limit of normal were observed in around 1 percent of clinical trial participants, generally at or after treatment week eight. 

Consequently, liver-related blood tests should be performed prior to starting therapy and at certain times during treatment, and Zepatier should not be given to patients with moderate or severe liver impairment, the regulator said.