UPDATE 1-Once-daily Schering hepatitis C drug shows promise

* 85-87 pct have no trace of virus after 12 wks

* Side effects similar to standard 2-drug combo

* Study of once-daily drug continues up to 36 weeks longer


NEW YORK, Nov 2 (Reuters) - An experimental newer treatment for hepatitis C being developed by Schering-Plough Corp showed impressive effectiveness and was well tolerated in an ongoing mid-stage study, researchers said on Monday, citing interim data.

The pill, narlaprevir, is the first once-a-day member of an emerging new class of treatments for hepatitis C called protease inhibitors. They prevent replication of hepatitis C, a virus that can badly harm the liver for decades before symptoms develop and which is believed to infect as many as 5 million Americans.

Narlaprevir was tested among subjects with genotype 1, the most common but most difficult to treat strain of the virus, who had not previously been treated for their infections.

Before taking the new drug, patients in two arms of the study were given "lead-in" treatment with a pair of standard drugs for four weeks -- Schering-Plough's SGP.N Pegintron form of interferon and an oral antiviral medicine called ribavirin.

They then added narlaprevir to their drug regimen, along with a low-dosage form of a widely used medicine for HIV called ritonavir meant to slow down the body’s breakdown of narlaprevir -- thereby making narlaprevir a once-daily treatment.

Among those taking the combination of four drugs, 85 to 87 percent achieved rapid virologic response (RVR) -- meaning they had undetectable levels of virus in their bloodstream after four weeks and were therefore deemed likely after months of further treatment to remain without trace of the virus.

That compared with a RVR rate of 58 to 75 percent among patients taking the four drugs that did not have the lead-in treatment, and no patients in another group that are only taking Pegintron and ribavirin during the study.

“These are preliminary data, but the RVR seen for narlaprevir is equal to or better than the RVR that has been reported for other protease inhibitors,” said Dr. John Vierling, chief of hepatology at Baylor College and lead investigator for the study.

He was referring to two other experimental medicines farther along in testing against hepatitis C. They include Vertex Pharmaceuticals Inc's VRTX.O telaprevir, which is given two or three times a day, and Schering-Plough's own boceprevir, given three times daily.

The interim data were presented at the American Association for the Study of Liver Diseases’ annual meeting in Boston.

Vierling said 85 to 87 percent of patients who took narlaprevir, ritonavir, Pegintron and ribavirin after lead-in treatment also achieved early virologic response (EVR), defined as undetectable hepatitis C at week 12 of narlaprevir treatment. That compared to 17 percent of patients who took Pegintron and ribavirin alone.

The EVR for narlaprevir patients was as good or better than the 70 to 80 percent EVR seen in separate trials of telaprevir and boceprevir, Schering-Plough said.

The incidence of side effects among patients taking the four-drug regimen that included narlaprevir was similar to that of patients receiving only Pegintron and ribavirin, except for an increase in anemia and lower counts of immune system cells called neutrophils.

“The side effect profile was very favorable; we didn’t have any major surprises,” said Vierling.

As the trial continues, all patients will now take Pegintron and ribavirin alone for an additional 12 or 36 weeks -- to make sure the virus is eradicated -- for a total eventual treatment period of 24 to 48 weeks.

Patients taking current standard therapy with an interferon and ribavirin are treated for a year, and less than half are able to eliminate the virus.

So the newer generation of protease inhibitors hold promise of potentially shortening therapy and doubling cure rates.

Vierling said narlaprevir is several years behind boceprevir and telaprevir in development, but has potential eventually to become the preferred drug because of its once-daily dosing.

“Once-daily treatment would be a major advance in terms of convenience, and helping patients comply with their treatment regimens,” he said.

Larger U.S. rival Merck & Co MRK.N is expected to acquire Schering-Plough in coming weeks, thereby becoming an instant global leader in the hepatitis C field. (Reporting by Ransdell Pierson; editing by Carol Bishopric)