The US Food and Drug Administration (FDA) has approved Pfizer Inc.'s Selzentry, the first in a new class of oral HIV medicines, according to media reports Tuesday.

The novel drug, also known as maraviroc, is the first anti-AIDS drug that works by blocking a crucial doorway, called the CCR5 receptor, that the HIV virus often uses to enter white blood cells. Older AIDS medicines attack the virus itself.

FDA approved Monday Selzentry for use in patients who have tried other medicines and for those for whom a diagnostic test has confirmed their HIV strain is linked to the CCR5 receptor. About 50 percent to 60 percent of patients who have been treated with other AIDS drugs meet that definition, the FDA said.

Pfizer, the world's largest drug maker, expects Selzentry to be available next month.

Selzentry will come with a "black box" warning, the strongest for prescription drugs, about the risk of liver toxicity.

 In the company's studies, about 45 percent of patients who took maraviroc had their HIV virus suppressed to undetectable levels. The same was true for 23 percent who got a placebo. All patients also were treated with a cocktail of the best available drugs and had tried other regimens.

Howecer, Selzentry's safety and effectiveness have not been established in adults or children who have never been treated with other HIV drugs, the FDA said, adding the drug has not been studied in pregnant women.

(Xinhua News Agency via Agencies August 7, 2007)