WHITEHOUSE STATION, NJ ( TheStreet) -- Vertex Pharmaceuticals ( VRTX - Get Report) defeats Merck ( MRK - Get Report) in the first battle of the hepatitis C drug war.

Merck said Wednesday that between 63% and 66% of hepatitis C patients never treated before achieved a viral cure after receiving the company's experimental drug boceprevir plus the standard of care, according to top-line results from a phase III study known as SPRINT-2.

These boceprevir cure rates were significantly higher than the 38% of hepatitis C patients cured using standard of care alone. On these data, Merck said it will seek approval of boceprevir in the U.S. and Europe by the end of the year.

If approved, boceprevir may have a tough time competing against Vertex's hepatitis C drug telaprevir, which will also be filed for approval later this year. Results from a similar Vertex study in so-called "treatment-naïve" hepatitis C patients released in May showed that telaprevir plus the standard of care achieved a cure rate of 75%.

Moreover, patients can be cured of the hepatitis C virus using Vertex's telaprevir in as little as 24 weeks, while the shortest treatment duration with Merck's boceprevir is 28 weeks.

It's important to note that boceprevir and telaprevir have never been matched head to head in a single study, but that doesn't stop analysts and investors from comparing the efficacy and safety of the two drugs.

"The boceprevir data look ok from an efficacy and safety standpoint but we believe that they are inferior to what telaprevir has demonstrated thus far," wrote ISI Group biotech analyst Mark Schoenebaum in an email to clients soon after Wednesday's announcement.

In early trading, Vertex shares were up 5% to $37.04. Merck was essentially flat at $34.85.

Merck Wednesday also released data from a second phase III study known as RESPOND-2 which tested boceprevir in patients who previously failed to respond to treatment with standard of care.

In this study, cure rates for boceprevir patients (who also received standard of care therapy) ranged from 59% to 66%. By comparison, patients who were re-treated with standard of care achieved cure rates of 21%.

Vertex is running a similar study of telaprevir in treatment-experience hepatitis C patients, with results expected in September.

Full data presentations for both telaprevir and boceprevir will be made at the American Association for the Liver Disease (AASLD) annual meeting in early November.

-- Reported by Adam Feuerstein in Boston.

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