UPDATE 2-Vertex hep C drug helps tough to treat patients

* 57 pct prior null responders achieve SVR on telaprevir

* 90 pct prior relapsers achieve SVR on telaprevir

* Vertex shares up 2.8 pct (Adds analyst comment, share price)

NEW YORK, Oct 28 (Reuters) - Vertex Pharmaceuticals Inc's VRTX.O closely watched hepatitis C drug telaprevir knocked out the virus in a significant number of patients who had failed to respond to standard treatments or relapsed after taking the standard drugs, according to a small study.

Interim results from an ongoing study, released on Wednesday, showed 57 percent of patients who failed to respond to the standard treatments of pegylated-interferon and ribavirin, and 90 percent of those who responded but later relapsed, achieved a sustained viral response when telaprevir was added to their regimen.

The percentage of patients in whom the virus is undetectable after completing treatment yields the critical measure known as sustained viral response, or SVR.

“Ninety percent in prior relapsers is very impressive and suggests that the rate in naive (previously untreated) patients could move up to the 75-80 percent range,” said Sanford Bernstein analyst Geoffrey Porges.

“The 57 percent SVR rate in prior null responders is also remarkable. By comparison such patients today have no possibility of an SVR with current therapy,” Porges added.

There was also a 55 percent SVR rate among patients on telaprevir who had appeared to be responding to prior standard treatment after 12 weeks, but still had detectable levels of the virus at week 24.

Telaprevir, an experimental treatment for the serious liver disease, is the most important drug in Vertex’s developmental pipeline and is expected to become its first commercial product, likely in 2011.

The company plans to file an application seeking U.S. approval of telaprevir in the second half of 2010.

“Despite small patient numbers, first SVR data in null responders look impressive,” Howard Liang, an analyst with Leerink Swann, said in a research note.

"We believe the new data reduce concerns about the impact of upcoming boceprevir null responder data at AASLD," Liang said, referring to a rival drug being developed by Schering-Plough Corp SGP.N.

Both Vertex and Schering will be presenting eagerly anticipated data at the upcoming American Association for the Study of Liver Diseases (AASLD) meeting in Boston, which begins later this week.

Patients in this open label study had been in the control groups of previous Phase II telaprevir trials and were then given the Vertex drug.

Of 117 patients enrolled in the study, data from 94 was included in the interim analysis, Vertex said.

Eight patients in the study discontinued treatment due to adverse side effects, including rash and anemia.

“The most impressive finding in this analysis is the low discontinuation rate due to adverse events,” Porges said. “The discontinuation rate of 7 percent and the rash rate of 3.5 percent are materially lower than the rates in the earlier blinded studies with telaprevir and pegylated-interferon.”

Vertex shares were up 93 cents, or 2.8 percent, at $34.30 in late morning trade on Nasdaq. (Reporting by Bill Berkrot, editing by Leslie Gevirtz and Tim Dobbyn)