HIV drugs to be used in prevention

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

"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 the agency's trials. "Clearly, this is one of the most promising things we have in the pipeline right now."

Some results are expected to be available 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 Mexico City 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 used to treat HIV infections and give it daily to people at risk of contracting the virus in order to block infections.

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 laboratory worker is accidentally stuck with a contaminated needle or when a nurse or emergency technician is exposed to HIV-positive blood.

"In all those circumstances, it works," Paxton 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. We need very low side effects and a high barrier to development of resistance," 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 in Northern California, is a combination of tenofovir and emtricitabine, drugs in a class known as non-nucleoside reverse transcriptase inhibitors, which block an enzyme necessary for HIV replication. Truvada is being used in many of the studies. The rest of the trials are using only tenofovir, which is trade-named Viread by Gilead.