Pfizer drug helps advanced HIV at 48-week mark

BOSTON (Reuters) - The Pfizer Inc. AIDS drug maraviroc helps thwart the HIV virus in nearly half of people who have developed resistance to other treatments, according to two related studies published on Wednesday.

At least 42 percent of patients in Europe, North America and Australia who took maraviroc once or twice a day on top of standard drug cocktails had blood virus counts below levels that cause visible damage to the immune system.

Only 18 percent of patients who got a placebo plus a standard HIV drug combination got their viral levels that low over the 48 weeks that have been studied so far.

In all, 1,049 volunteers who were resistant to three of the six classes of HIV drugs were involved in the two Pfizer-sponsored studies, reported in the New England Journal of Medicine.

Industry analysts have said maraviroc could be worth $500 million to Pfizer by 2011. Marketed as Celsentri in Europe and Selzentry in the United States, it was approved a year ago based on 24-week results from the two studies.

Maraviroc stops the virus from getting into the immune cells it affects by blocking a doorway called the CCR5 co-receptor. It was given with other HIV drugs that target the ability of the virus to replicate.

The volunteers, all with advanced human immunodeficiency virus infections, were screened to be sure they carried a strain of the virus that uses CCR5. More than half of infected people do.

The researchers said maraviroc did not produce any unusual side effects and, although the drug carries a warning about possible liver problems, "our study simply didn't see liver toxicity, so that's reassuring," said Dr. Roy Gulick of the Weill Cornell Medical Center in New York, who led the study.

In a telephone interview, Gulick said the liver warning was "based on a single case, and that patient had a lot of complicating factors, so there are other possible reasons why they ran into liver trouble."

An estimated 33 million people worldwide are infected with HIV. There is no cure and no vaccine, although a drug cocktail can help control infection and keep people healthy.

But the virus mutates constantly and usually becomes resistant to the drugs after a while, meaning patients must switch to different cocktails. AIDS experts say they need constant new additions to the list of 20 or so existing HIV drugs.

Maraviroc belongs to a new class of these drugs, called HIV entry inhibitors or CCR5 receptor antagonists.

Gulick said results from the 96-week mark are now being analyzed and may be presented at a scientific meeting in November.

(Editing by Maggie Fox and John O'Callaghan)