The federal Food and Drug Administration approved a new non-nucleoside reverse transcriptase inhibitor for use in treating persons with HIV who are resistant to other drugs in that class. Etravirine, sold under the name Intelence, was developed by Tibotec Pharmaceuticals, a division of Johnson & Johnson. The announcement was made January 18.

Existing drugs in the NNRTI class, nevirapine (Viramune) and efavirenz (Sustiva), are a powerful part of combination therapies that are widely used. However, HIV develops resistance to them more rapidly than any other class of drugs. Often only a single key genetic mutation is sufficient to confer resistance to both of those drugs.

The great strength of etravirine is that it works against virus that has developed resistance to those two earlier drugs in the class. In the DUET 1 and 2 clinical trials, patients resistant to the NNRTIs received an optimized background therapy and were randomized to receive either etravirine (599 patients) or placebo (604) twice a day.

After 24 weeks, the patients receiving etravirine were more likely to have their viral load suppressed below 50 copies (59.8 percent versus 40.2 percent), and had a greater increase in their CD4 T-cell count (81 T-cells versus 64 T-cells).

Side effects generally were mild. However, possible drug-drug interactions preclude etravirine's use with other drugs metabolized through the same pathway in the liver. That list includes ritonavir, which is used to "boost" many of the protease inhibitors.

A patient whose virus develops resistance to current NNRTIs likely would switch to another class of drugs, such as a protease inhibitor, rather than add etravirine to the regimen. It is likely to be used only when other treatment options narrow considerably.

Etravirine is not approved for use as part of an initial therapy in treating HIV; Tibotec is developing another drug for that purpose.

Dr. Debra B. Birnkrant, director of the FDA's Division of Antiviral Products, said, "This is another significant new product for many HIV-infected patients who are NNRTI-resistant and whose infections are not responding to currently available medications."

The wholesale acquisition cost for Intelence, or the "list price" from which large organizations often negotiate a discount, is $21.80 a day. A comparable price for efavirenz is about $15 a day.

"We're all pretty pleased with that," said Martin Delaney with Project Inform. "This price beats all of [the more recently approved drugs for salvage therapy] by several dollars a day."