UPDATE 2- Merck hepatitis drug works, side effects loom

Wed Aug 4, 2010 10:22am EDT

* Merck to seek boceprevir approval by year's end
* Side effects raise questions in one of two trials
* Shares of rival drugmaker Vertex rise 6 pct
* Merck shares unchanged (Adds details from study, bylines)

By Ransdell Pierson and Lewis Krauskopf

NEW YORK, Aug 4 (Reuters) - Merck & Co (MRK.N) said on Wednesday that two late-stage studies of its experimental hepatitis C treatment met their main effectiveness goals, and it expects to seek approval for the high-profile medicine by the end of the year.

But a much higher percentage of patients taking the Merck drug dropped out of one of the trials due to adverse events, including anemia, than those taking standard treatments -- which themselves are known for harsh side effects.

Merck's drug, boceprevir, was one of the most important experimental products gained by Merck through its acquisition of Schering-Plough Corp last year.

It and a similar drug being developed by Vertex Pharmaceuticals Inc (VRTX.O), called telaprevir, have been considered possible blockbuster products because of their potential to cure more patients and in as little as half the time of standard drugs that require almost a year of treatment.

Vertex shares rose almost 6 percent to $37.23, as investors studied the general findings Merck provided. Merck said it would provide detailed clinical trial data at a medical meeting in November. Merck shares were unchanged.

The new class of drugs work against the liver-damaging hepatitis C virus by blocking a protein called protease that the virus requires to replicate. Current treatments, by contrast, involve a combination of the injectable drug interferon and an anti-viral pill called ribavirin.

Merck said boceprevir, taken in combination with the company's Pegintron brand of interferon and ribavirin, significantly increased the number of patients with sustained virologic response -- meaning no detectable virus levels 24 weeks after the end of treatment -- compared with patients receiving Pegintron, ribavirin and a placebo.

One of the trials, called HCV RESPOND-2, involved 403 patients with genotype 1, the most common form of hepatitis C, who had failed prior therapy with interferon and ribavirin. The other trial, called HCV SPRINT-2, enrolled 1,097 patients with genotype 1 who had not previously been treated for the virus.

In both trials, a significant number of patients received 48 full weeks of treatment. But patients with undetectable virus at week 8 and again at certain points later in the studies were able to stop all treatment at 36 weeks in the smaller trial, and at 28 weeks in the larger study. (Reporting by Ransdell Pierson and Lewis Krauskopf, editing by Maureen Bavdek, Dave Zimmerman)

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