The drug already is widely used as part of a drug regimen given to people who may have been exposed to the virus. Health workers who are stuck by a needle, for instance, take a mix of medications, including tenofovir, for 30 days to reduce their chance of becoming infected.
Studies also have shown that the medication may help prevent infection in healthy monkeys.
Marc Conant, an HIV doctor in San Francisco, said he recently began prescribing tenofovir to two uninfected men after they told him they were very sexually active and would not use condoms. Though troubled by the fact that the drug hasn't been proven effective for such a use and that his patients may be increasing their risky behavior while using it, he says using the drug is better than taking no precaution at all.
"What choice do I have? Forty-thousand people are still getting infected every year," he said. "Everyone knows condoms work, but they're not using them. All I am trying to do is reduce the risk that people harm themselves."
Conant said he tests both patients every three months and that they remain negative.
Tenofovir works by blocking an enzyme the virus needs to replicate. Although other AIDS medications may also have protective effects, researchers believe that tenofovir is especially promising at reducing the risk of transmission because the drug has few side effects and remains in the body for up to two days.
Dan Uhler, a prevention counselor at a San Diego gay men's health clinic, said the drug first appeared about a year ago in gay clubs and at circuit parties, festival-size dance parties known for sex and substance abuse. It is sometimes sold with other drugs such as Ecstasy and methamphetamines for around $100. People who use tenofovir believe it "helps justify the risks they are taking," Uhler said.
The growing use of the drug comes as HIV prevention efforts appear to be losing effectiveness among gay and bisexual men. Nationally, new HIV infections remain at around 40,000 a year, but a recent report released by the CDC found that last year new infections among gay and bisexual men rose 8%. A separate CDC report, released in October, found that syphilis rates among these men has climbed 29% over the last four years, indicating a spike in risky sexual activity.
Steven Gibson, director of a gay men's health clinic in San Francisco, said the city's public health department should educate the community about the dangers of taking tenofovir in unapproved ways.
