Merck’s effort to expand its footprint in the lucrative hepatitis C market stumbled, with an experimental four-week, triple-therapy regimen proving largely ineffective.

Results of a Phase II study evaluating the combination of Merck’s investigational compounds grazoprevir and elbasvir with Gilead Sciences’ blockbuster Sovaldi (sofosbuvir) in 102 treatment-naïve genotype 1 HCV patients, both with and without liver cirrhosis, were mixed, the drugmaker said.

Only 12 out of 31 enrolled patients, or 38.7 percent, achieved functional cures after four weeks of treatment, Merck said. Nineteen subjects, or 61.2 percent, relapsed within 12 weeks after dosing.

On the other hand, the triple-therapy demonstrated functional cure rates in 80 percent of cirrhotic patients treated for six weeks, as well as 86.7 percent of non-cirrhotic patients treated for six weeks and 94.7 percent of non-cirrhotic patients treated for eight weeks.

“These findings will inform the design of larger studies aimed at understanding the potential of short-duration triple therapy,” said lead investigator Eric Lawitz, M.D., vice president of scientific and research development at the Texas Liver Institute.

Merck spokeswoman Sarra Herzog declined to comment on whether the company would continue with the triple therapy. But she did say Merck plans to begin a new set of Phase II trials evaluating grazoprevir/elbasvir with another investigational drug called MK-3682, as well as the combination of grazoprevir with MK-3682 and MK-8408 in HCV patients without liver cirrhosis.

Seven other Phase II trials of grazoprevir and elbasvir, with or without ribavirin, are set to be completed next year, and one Phase III trial has a completion date of April 2016. — Lena Freund

Originally appeared in Drug Industry Daily, the pharmaceutical industry’s number one source for regulatory news and information. Click here for more information.