Merck four-week hep C regimen with Gilead's Sovaldi comes up short

(Reuters) - An attempt by Merck & Co to shorten hepatitis C treatment to just four weeks by adding Gilead Sciences Inc's huge selling Sovaldi to its own oral two-drug combination came nowhere near the desired efficacy due to a high rate of relapses, according to interim data from a midstage study.

Several companies have been working to find ways to further reduce the number of weeks of treatment needed, while keeping cure rates above 90 percent.

A just approved pill called Harvoni that combines Sovaldi with another Gilead drug requires eight weeks of treatment for many patients, and longer for tougher to treat patients.

In the ongoing Merck trial of previously untreated patients, only 38.7 percent had no detectable sign of the liver destroying virus after four weeks of treatment with Sovaldi and Merck's grazoprevir/elbasvir combination. Nineteen of the 31 patients in the four-week treatment arm relapsed prior to the planned end of the study, which is 12 weeks after completion of dosing.

The preliminary data was set to be presented on Monday at the American Association for the Study of Liver Diseases (AASLD) meeting in Boston.

The best result so far in the multi-arm, three-drug study called C-Swift was observed with eight weeks of treatment of patients with cirrhosis in which 94.7 percent had no detectable virus. They will be deemed cured if the virus has not reappeared 12 weeks after stopping treatment.

With a six-week regimen in non-cirrhotics, 86.7 percent of patients had no sign of virus up to 8 weeks after completing treatment, according to the interim results.

"These findings will inform the design of larger studies aimed at understanding the potential of short-duration triple therapy across multiple patient types," Dr. Eric Lawitz, the study's lead investigator, said in a statement.

The three drugs each work in a different way to help prevent the virus from replicating. But following failure of the 4-week experiment, Merck said it will turn its attention to studying a combination of three of its own drugs in development rather than involving the Gilead medicine in future studies.

The hepatitis C field has been moving at a lightning pace. Only a handful of years ago, patients needed 48 weeks of treatment with drugs that had harsh side effects and only cured about 40 percent of patients.

The new all-oral treatments eliminate the need for injectable interferon and its flu-like side effects, as well as another older drug called ribavirin that caused anemia and other problems, while dramatically increasing cure rates and reducing treatment duration.

(Reporting by Bill Berkrot; Editing by Chris Reese)