Researchers using existing HIV drugs prophylactically

Researchers focus on prophylactic approach -- give drugs to those at risk to block HIV infections.

Last update: August 4, 2008 - 8:46 PM

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Disheartened by the failures of vaccines and microbicides in blocking HIV transmission, some AIDS researchers are now touting a third possibility: using existing HIV drugs prophylactically.

As many as 15,000 people worldwide will be enrolled in trials to test the concept by next year -- more than are enrolled in all vaccine and microbicide trials combined -- according to a report issued Sunday evening at the International AIDS Conference in Mexico City.

"We need to look for new ways that people can protect themselves," said Dr. Lynn Paxton of the U.S. Centers for Disease Control and Prevention, who is coordinating that agency's trials of the approach. "Clearly, this is one of the most promising things we have in the pipeline right now."

No results are available yet and probably won't be until next year.

"We don't know if this is going to work or not, but we must get it on the agenda," said Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition, which prepared the report. "We must be prepared for the answers we do get."

The concept, called Pre-Exposure Prophylaxis or PrEP, is relatively simple: Take a drug that is useful for treating HIV infections and give it daily to at-risk people to block the infections before they occur.

A similar approach is now used routinely for people who are going into areas where malaria or tuberculosis are endemic and for AIDS patients who are at risk of pneumocystis pneumonia.

AIDS drugs are also used to block mother-to-child transmission during birth or breast-feeding and for post-exposure prophylaxis, such as when a nurse or emergency technician is exposed to HIV-positive blood. "In all those circumstances, it works," Paxson said. "The logical extension is to think about it for prevention of sexual or injection-drug transmission."

Researchers have been arguing for PrEP for years, she said.

"The only thing that held us back is we didn't have any drugs amenable to that," she said. "It wasn't until Truvada came down the pipe that we had the pills to test it." Truvada, manufactured by Gilead Sciences Inc. of Foster City, Calif., is a combination of the non-nucleoside reverse transcriptase inhibitors tenofovir and emtricitabine, and is being used in many of the studies.

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