CORRECTED - Vertex hepatitis C drug effective in trial

(In eighth paragraph, corrects to show virus was eradicated for three months, not six, following treatment)

BOSTON, Nov 2 (Reuters) - Vertex Pharmaceuticals Inc's (VRTX.O) experimental hepatitis C drug is more effective than existing treatments and works in half the time, but also causes significantly more side effects.

Data to be presented at the Annual Meeting of the American Association of the Study of Liver Diseases show the drug, telaprevir, in combination with standard treatment, eradicated the hepatitis C virus in more than 60 percent of patients who took it as part of a 24-week treatment.

Eradication of the virus is based on a measure known as sustained viral response, in which the virus remains at below detectable levels.

Typically, not more than 50 percent of patients taking standard treatments see their virus eradicated and the typical length of treatment is 48 weeks.

Hepatitis C is a blood-borne liver disease that can cause chronic liver disease, liver cancer and cirrhosis. It affects about 170 million people worldwide.

In a mid-stage trial conducted in the United States known as PROVE 1, 61 percent of 79 patients who took telaprevir in combination with the standard treatments, pegylated interferon and ribavirin, saw the virus fall to undetectable levels in their blood and remained undetectable six months after treatment was stopped.

But 13 percent of patients discontinued the trial in the first 12 weeks because of side effects. The most common side effect was rash.

In a separate mid-stage trial known as PROVE 2, conducted in Europe, 65 percent of patients who took part in the 24-week treatment regime -- which consisted of 12 weeks of triple therapy followed by 12 weeks of standard treatment -- saw the virus eradicated and stay eradicated after three months.

In the PROVE 1 trial, the relapse rate was 2 percent. In PROVE 2 it was 14 percent. Patients who take standard therapy typically relapse at a rate of 20 percent to 30 percent, Vertex said.

The difference in relapse rate between the two trials stemmed from the fact the PROVE 1 trial results were based only on patients who were least likely to relapse in the first place, based on the rapidity of their initial response to the drug.

In the PROVE 2 trial, which did not just measure patients who saw a quick drop in virus after starting therapy, 14 percent of patients relapsed.

Telaprevir is one of a new class of drugs that inhibits a hepatitis C protease, an enzyme essential for the virus to replicate. Vertex's partner on the drug is Tibotec Pharmaceuticals Ltd, of Cork, Ireland. (Reporting by Toni Clarke, Bill Berkrot)