FDA panel backs speedy approval for Merck HIV drug

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An FDA appointed panel of outside medical experts has unanimously backed the accelerated approval of Merck's new first-in-class HIV drug Isentress (raltegravir) for patients who have failed treatment with other HIV drugs.

Under the accelerated approval process, time is trimmed off the standard approval period for compounds deemed an advance over existing therapies by the FDA.

In June, the FDA granted Merck's Isentress application priority review status, indicating the drug addresses an urgent medical need. As a result, Isentress' review time was "fast-tracked" to six months, instead of the 10 months the process often takes under standard review.

The FDA usually follows the recommendations of its advisory panels, although it isn't required to do so.

If approved, Isentress would be the first in a new class of antiretroviral agents called integrase inhibitors that inhibit the insertion of HIV DNA into human DNA.

Inhibiting integrase from performing this function blocks the ability of the virus to replicate and infect new cells. There are drugs in use that inhibit two other enzymes critical to the HIV replication process -- protease and reverse transcriptase -- but currently no approved drugs inhibit integrase.

The drug is designed to be used in combination with other AIDS treatments, although the panel did not specify which drugs should be used with Isentress.

Merck estimates that between 20,000 and 40,000 US HIV patients would qualify to take Isentress if it is approved.

Joe Tooley, an analyst for A.G. Edwards, said in a published report that sales for Isentress could reach $750 million in annual sales by 2011.

Last month, the FDA granted approval to Pfizer's Selzentry (maraviroc) HIV treatment, another first-in-class HIV treatment. Selzentry works by blocking viral entry into white blood cells, significantly reducing viral load and increasing T-cell counts in treatment-experienced patients infected with a specific type of HIV. Selzentry was granted approval under priority review status. Analysts have projected sales of Selzentry to reach $500 million by 2011.

Meanwhile, Johnson & Johnson is awaiting FDA approval for its new AIDS drug known as TMC-125, also designed to be used by patients who have failed treatment with other HIV drugs.

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