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New AIDS Drug 'Incredibly Encouraging'

Isentress Works When All Other AIDS Drugs Fail, Study Shows
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WebMD Health News
Reviewed by Louise Chang, MD

March 1, 2007 -- "Incredibly exciting." "Road to hope." "Very exciting." "A very important milestone in HIV treatment history."

That's what major AIDS researchers are saying about Isentress, the first of a new class of HIV drugs. Early results from two major clinical trials of Isentress were reported this week at the largest annual U.S. HIV conference.

Patients in the studies had run out of treatment options. After a decade of treatment, the HIV in their bodies had become resistant to at least one drug in each of the three classes of AIDS therapies. Their immune systems had begun to fail and they had high blood levels of HIV.

But when these patients took Isentress in combination with other powerful AIDS drugs, nearly 80% of patients saw their HIV levels plummet to near-undetectable levels after 16 weeks of treatment. Without Isentress, state-of-the-art treatment helped only 43% of patients to this degree.

Joseph J. Eron Jr., MD, of the University of North Carolina-Chapel Hill, reported the combined findings from the studies at the 14th annual Conference on Retroviruses and Opportunistic infections.

"This is a very important milestone in HIV treatment history," Eron tells WebMD. "These are results we would have been happy with in treatment-naive patients. And these are our most drug-experienced, drug-resistant patients -- the ones for whom it is most difficult to come up with treatment options.

"It really moves us into an era where even our most treatment-experienced patients have the opportunity to get their virus below detectable limits," Eron adds.

New AIDS Drug, New HIV Target

HIV makes three proteins, called enzymes, which it needs to infect human cells. The AIDS virus uses its reverse transcriptase enzyme to translate its RNA genetic code into DNA. Later, after it has made human cells produce new viral proteins, it uses its protease enzyme to snip the proteins into the right size.

Nearly all existing HIV drugs block either reverse transcriptase or protease. But Isentress blocks an enzyme called integrase. HIV needs integrase to integrate its newly translated DNA into the DNA of human cells.

Researchers have worked for years to develop an integrase inhibitor. Until recently, that goal was elusive. Now that work is paying off. Isentress, from Merck, is the first of its kind. But others are on the way.

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