UPDATE 2-US FDA panel recommends Merck AIDS drug

(Adds market estimate, AIDS, drug class details, byline)

SILVER SPRING, Md., Sept 5 (Reuters) - Merck & Co Inc's MRK.N experimental AIDS drug Isentress merits approval, a panel of expert advisers to the U.S. Food and Drug Administration said on Wednesday.

The advisory panel voted unanimously to recommend marketing approval for the twice-a-day pill, known generically as raltegravir, the first in a novel class of AIDS treatments to go before regulators.

The FDA will make the final decision on approval, but usually follows the advice of its expert panels. Merck anticipates an FDA decision by mid-October, based on a speedy review granted by the FDA for unmet medical needs.

If approved, it would be the first in a new class of HIV medicines called integrase inhibitors that aim to block insertion of HIV genetic material into human DNA to prevent replication of the virus.

Matt Sharp, a Chicago-based AIDS activist who testified at the hearing and who is on the treatment, called the drug a major advance. “My case shows that raltegravir is going to save lives. It’s a very unique time in the history of HIV treatment ... with several new agents available.”

Cowen & Co. analysts have said the drug could reap sales of $1 billion by 2012. The drug could compete with a similar treatment being developed by Gilead Sciences GILD.O known as GS-9137.

The drug was tested in patients who have become highly resistant to current HIV medicines. Resistance is a problem as the human immunodeficiency virus (HIV) that causes AIDS can mutate, particularly if patients fail to rigorously follow complicated regimes.

Still, one worrisome trend discussed at length at the panel meeting is the higher cancer rate in patients treated with the Merck drug. Twenty malignancies were seen in the Merck group, compared with one malignancy within control groups, according to FDA data.

The cancer types were varied but tended to be those often associated with AIDS, Merck noted.

“There is no doubt that this is a great drug, absolutely, and it’s very useful for patients who’ve experienced lots of failure. That’s not the issue,” Peter Havens, professor of pediatrics and epidemiology at Medical College of Wisconsin, said.

If there is “significant potential risk, then expanding the population, without thinking about it, is potentially very dangerous,” he said during the panel meeting.

Havens is one of several panel members who urged the FDA to limit the labeling to patients who have failed multiple types of therapies, rather than the broader “treatment experienced,” requested by Merck.

Merck studied the drug in patients who failed many therapies.

Havens and another panel member said they were confident the FDA would take their concerns into account when crafting the label.

The panel also advised the FDA to require Merck to do follow-up studies on patients for up to five years, though many lamented the FDA’s lack of authority to require Merck to complete them.

The issue of FDA’s enforcement power is being discussed in the U.S. Congress, as it mulls legislation giving the agency more power to enforce so-called post-marketing studies.

Because of advances in treatment, more people are living with HIV or AIDS than ever before. From 2001 to 2005, the numbers of those living AIDS in the United States rose 27 percent to about 422,000 people, according to the U.S. Centers for Disease Control and Prevention.