03/06/2012 03:09 pm ET Updated May 06, 2012

Victrelis And Incivek, Rival Hepatitis C Drugs, Both Work In HIV Patients, Studies Find

* Vertex posts 12-wk virologic response rate of 74 pct

* Merck posts 12-week virologic response rate of 60.7 pct (Adds comments, details)

By Deena Beasley

SEATTLE, March 6 (Reuters) - Rival hepatitis C drugs from Merck & Co Inc and Vertex Pharmaceuticals Inc are effective in patients also infected with HIV, the virus that causes AIDS, according to data released on Tuesday.

The Vertex drug had the more impressive results, the data showed.

The results from midstage trials follow notification last month from U.S. regulators and Merck that use of the company's Victrelis drug in such "co-infected" patients could lessen the effectiveness of some medicines used to treat patients infected with the human immunodeficiency virus, or HIV.

Those findings involved "boosted" HIV protease inhibitors.

Both Victrelis, also known as boceprevir, and Vertex's Incivek, or telaprevir, are protease inhibitors designed to block an enzyme that the hepatitis C virus requires to replicate.

Since key HIV drugs are also protease inhibitors, which use the same pathway as the new hepatitis C drugs, there is a potential for drug interaction, said Dr. Douglas Dietrich, professor of medicine at New York's Mount Sinai School of Medicine and lead investigator on the Incivek trial.

He said 74 percent of trial patients treated with Incivek followed by the standard regimen of interferon and ribavirin were free of the hepatitis C virus, or HCV, 12 weeks after ending treatment, compared with 45 percent of patients given interferon and ribavirin alone.

There were no instances of a rebound of HIV for patients in the Incivek trial. Side effects seen more frequently with the drug were itching, headache, nausea, rash, fever and depression. No cases of severe rash were reported.

Merck's Phase II trial found that 60.7 percent of patients treated with Victrelis and the standard hepatitis C therapy were free of HCV 12 weeks after treatment, compared with 26.5 percent of patients treated only with interferon and ribavirin.

Three patients on Victrelis and four in the control group had an increase in HIV.

"These Phase II trials, albeit small in size, demonstrate significant improvement" over treatment with interferon and ribavirin alone, said Dr. Mark Sulkowski of Johns Hopkins University School of Medicine in Baltimore, the lead investigator on the Victrelis trial.

The trial results were reported in Seattle at the Conference on Retroviruses and Opportunistic Infections on Tuesday.

"The drugs that are used to treat HIV have certain metabolic effects," said Eliav Barr, Merck's vice president, infectious diseases. "You have to be careful not to mess with those drug levels."

Barr estimated that between 15 percent and 20 percent of U.S. HIV patients are also infected with HCV, a liver-destroying virus which has come to be a leading cause of death for HIV patients.

In the first half of this year, Merck plans to start a larger, pivotal trial of Victrelis in a broader range of HIV patients, with those results expected a couple of years later, Barr said. The company is also conducting a number of drug interaction studies.

Vertex said it is currently enrolling patients in a Phase III study of Incivek combination regimens in people also infected with HCV and HIV.

According to the U.S. Centers for Disease Control and Prevention, 1.2 million Americans have HIV, and one in five adults with HIV do not know they are infected.

Vertex said laboratory studies of Incivek and HIV protease inhibitors had found no harmful effects on antiviral activity when combined with HIV medicines Agenerase (amprenavir) from GlaxoSmithKline Plc, Prezista (darunavir) from Johnson & Johnson's Janssen unit and lopinavir. Slight antagonistic effects were observed on the antiviral activity of Reyataz (atazanavir) from Bristol-Myers Squibb Co.

Merck said last month that a study among healthy volunteers showed Victrelis as lessening the effect of a combination of HIV drug Norvir (ritonavir) from Abbott Laboratories Inc with one of three other anti-HIV pills: Reyataz, Prezista and Abbott's Kaletra (lopinavir/ritonavir).

In afternoon trading, Vertex shares were down 77 cents or 1.9 percent to $39.63 and Merck shares were down $1.04 or 2.7 percent to $37.41 As the broad market fell. Merck said earlier its first-quarter earnings would trail Wall Street estimates. (Editing by Michele Gershberg and Gerald E. McCormick)