By Bill Berkrot

Nov 2 (Reuters) - A combination of two oral hepatitis C treatments developed by Merck & Co led to high cure rates in previously untreated patients, indicating the company is a contender in the race to find new treatments for the liver destroying virus.

The treatments tested with and without the older drug ribavirin led to cure rates of 96 percent to 100 percent, according to interim data from a small midstage clinical trial.

The results appear to confirm Merck will be competitive in the crowded race to develop interferon-free treatments for hepatitis C, assuming they are repeated in larger studies that include more difficult to treat patient populations, such as those not helped by prior therapy.

The 65-patient, 3-arm study tested MK-5172, a protease inhibitor, combined with MK-8742 from a highly promising new class of drugs called NS5A inhibitors for 12 weeks of treatment.

Based on data available at the time the interim results were released, 55 of 56 patients who completed the therapy were considered to be cured of the virus which is transmitted through infected blood from sources such as infected hypodermic needles or blood transfusions.

Patients who have no detectable levels of the virus in their blood 12 weeks after completing 12 weeks of treatment were deemed to be cured - a measure known as SVR 12, for sustained virologic response.

In the arm of the study that did not include the older oral medicine ribavirin, all 11 patients who completed therapy with MK-5172 and the higher 50 milligram dose of MK-8742 taken once a day achieved SVR 12.

All 12 patients who began that arm of the study had Genotype 1b of the liver disease, which is prevalent in Europe and Japan. It is considered somewhat easier to treat than Genotype 1a, the most common form of the virus seen in the United States, which may require a third drug in the regimen to achieve similarly high cure rates.

The other two arms - one testing 50 mg of MK-8742 and one using 20 mg - did include ribavirin given twice a day.

With the lower dose of the NS5A inhibitor, all 21 patients who completed therapy were deemed cured. In the group that received the higher dose in the three-drug combination, 23 of 24, or 96 percent, reached SVR 12. About three quarters of the patients in those arms were Genotype 1a.

Of the 65 patients in the study, only one had experienced a relapse of the virus, according to the data to be presented on Sunday at the American Association for the Study of Liver Diseases (AASLD) meeting in Washington.

"We are encouraged by these preliminary data for the combination of MK-5172 and MK-8742. It's a one-two punch with both arms equally strong," said Eliav Barr, head of infectious diseases for Merck.