Updated with new information throughout.

CAMBRIDGE, Mass. (

TheStreet

) --U.S. regulators on Monday approved Incivek, a new hepatitis C drug from

Vertex Pharmaceuticals

(VRTX) - Get Vertex Pharmaceuticals Incorporated Report

.

And now, Vertex's executives and employees can breathe a sigh of relief and get to work marketing Incivek against its main hepatitis C rival

Merck

(MRK) - Get Merck & Co., Inc. (MRK) Report

.

Not that Incivek's U.S. approval was ever in doubt, but the level of anxiety at Vertex must have been a tad high given that

Merck received U.S. Food and Drug Administration approval for its Hep C drug Victrelis

on May 13, followed by a recommendation for European approval last Friday.

Vertex shares were down 24 cents to $54.76 in Monday trading.

Incivek's approval was widely expected but in what could be considered an upside surprise, FDA did not saddle the drug's label with a black-box safety warning or a risk management plan concerning rash -- the drug's most widely publicized side effect.

Vertex said Incivek will be shipped to pharmacies this week. The company was expected to announce pricing for the drug on a conference call later this morning.

The Incivek label includes just two relatively straightforward treatment options of 24 or 48 weeks. Both regimens include the same 12-week course of Incivek, the only difference is the length of interferon and ribavirin use. Patients who have a strong, early response can stop all therapy at 24 weeks, which cuts treatment time in half compared to the old standard of care.

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Vertex studied Incivek in the hardest-to-treat null responder patients and cured about 32% of them compared to 5% cured with interferon and ribavirin alone. For the best-responding patients, cure rates approach 80%. The most common and noteworthy side effect of Incivek is rash, sometimes severe.

The simpler dosing schedule for Incivek and higher cure rates, particularly for those patients who failed previous treatment, is expected to give Vertex a marketing edge over Merck and Victrelis, which is priced at $1,100 per week or $26,000 to $48,000 for a full course of treatment, depending on the duration.

Figuring out how long to treat patients with Victrelis is more complicated. The drug's label includes four different treatment suggestions ranging from 26 weeks to 44 weeks. Doctors must first start patients on a four-week lead in of interferon and ribavirin before adding Victrelis. The course of Victrelis should be 28, 36, or 44 weeks long depending on how patients respond at various time points.

The stakes are high in the new hepatitis C treatment market. Approximately 3.2 million Americans are infected with the viral disease that attacks and progressively destroys the liver. Most people infected with hepatitis C don't know they have the disease and aren't diagnosed until liver damage occurs, which can take years.

"With the approval of Incivek, there are now two important new treatment options for hepatitis C that offer a greater chance at a cure for some patients with this serious condition," said Edward Cox, director of FDA's Office of Antimicrobial Products. "The availability of new therapies that significantly increase responses while potentially decreasing the overall duration of treatment is a major step forward in the battle against chronic hepatitis C infection."

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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