* 75 pct SVR rate seen with 12-week telaprevir regimen
* Patients on standard drugs had 44 pct SVR rate
* Shares rise 12 percent after hours (Adds company comment)
By Bill Berkrot
NEW YORK, May 25 (Reuters) - A hepatitis C treatment being developed by Vertex Pharmaceuticals Inc (VRTX.O) led to a 75 percent cure rate in a pivotal trial of previously untreated patients, the company said on Tuesday.
The results from the first late-stage Phase III study of telaprevir came in at the high end of expectations for a cure rate of 70 to 75 percent, with slightly lower discontinuation rates due to side effects than previously seen.
Vertex shares, which have slumped recently, were up 12 percent in after-hours trading.
Telaprevir is expected to become a multibillion-dollar drug for Vertex if approved by the U.S. Food and Drug Administration.
Seventy-five percent of patients who received 12 weeks of telaprevir in combination with current standard treatment of pegylated interferon and ribavirin, followed by either 12 or 36 weeks of standard treatment achieved a sustained virologic response, or SVR, which is tantamount to a cure.
That compared with a 44 percent SVR rate for patients who received the usual 48-week regimen of the standard drugs.
"I think it is a bellwether day for hepatitis C drug development. It's really impressive to see a 75 percent SVR rate in a Phase 3 pivotal trial," said Sanford Bernstein analyst Geoffrey Porges.
He said the result "sets a very high hurdle for competitors."
Porges previously had said a telaprevir SVR rate below 65 percent would be a disappointment and anything north of 80 percent would send the stock skyrocketing.
A member of Porges' household maintains a long position in Vertex, according to the BernsteinResearch website.
Telaprevir is in a race with a similar drug called boceprevir being developed by Merck & Co (MRK.N).
Data from two more Phase III trials of telaprevir, including results in patients who failed with previous treatment, is expected in the third quarter. The first boceprevir late-stage data will be released later this year.
Through mid-stage studies, most analysts have said the Vertex drug as superior.
In a third arm of the Phase III study, 69 percent of patients who received the telaprevir combination for just eight weeks followed by either 16 or 40 weeks of the standard drugs achieved SVR, Vertex said.
The results were "in line with what the Street was looking for, but certainly not above expectations, or below them for that matter," said Brian Skorney, an analyst for Thinkequity.
There has been great hope for this new class of antiviral drugs for the serious liver disease because of the potential for significantly higher cure rates and the possibility of cutting the duration that the standard drugs must be taken.
The tough to tolerate interferon and ribavirin offer cure rates in the 40 percent to 50 percent range, must be taken for 48 weeks, and often cause debilitating flu-like symptoms, leading many patients to discontinue their use.
"These results show that 75 percent of patients in the 12-week telaprevir arm achieved a viral cure, with the majority receiving only 24 weeks of therapy, marking what we believe may be a potentially dramatic improvement in the future treatment of hepatitis C," Vertex Chief Medical Officer Robert Kauffman said in a statement.
Several drugmakers, including Vertex, are working on next generation drugs with the hope they could be combined with treatments like telaprevir and eliminate the need for interferon altogether.
Telaprevir discontinuation rates due to adverse events were a bit lower than those seen in Phase II studies.
"Discontinuations due to rash were lower," Skorney said.
The discontinuation rate was 6.9 percent in the 12-week telaprevir arm, 7.7 percent in the 8-week arm and 3.6 percent with the standard drugs alone.
Viral relapse rates -- patients who had achieved undetectable levels of the virus in the blood only to relapse after completing treatment -- were much lower in the telaprevir arms of the study.
The relapse rate was 8.6 percent among patients who received 12 weeks of telaprevir and 9.5 percent for those who got the Vertex drug for 8 weeks. That compared with a 28 percent viral relapse rate on the standard drugs.
"The results highlight that telaprevir-based combination regimens may increase viral eradication rates and shorten treatment time for many patients," Dr Ira Jacobson from Weill Cornell Medical College and a researcher for the study, said in a statement.
Vertex shares rose to $38.10 in after hours trading from their Nasdaq close at $33.95. (Reporting by Bill Berkrot; additional reporting by Deena Beasley in Los Angeles; editing by Carol Bishopric, Leslie Gevirtz)