But demand is likely to extend around the world, said Drexel University AIDS researcher Seth Welles. Wherever they live, he said, "people don't like latex." And that means they engage in lots of unprotected sex.
Larger studies are testing the drug both in gel form and as a pill taken before sex. And researchers are beginning to examine whether it could prevent transmission of the virus between men.
While preliminary, the results so far were promising enough to generate a round of cheers when presented at an international AIDS meeting in Vienna last week.
The findings came from a trial that enrolled 889 women, half of whom got the drug and half a placebo. They were instructed to apply the vaginal gel up to 12 hours before having sex and again soon afterward.
The gel's effectiveness wasn't perfect, but the women in the trial didn't use it every time. After 21/2 years, 38 women in the drug group became HIV-positive compared with 60 in the control group. That amounts to a 39 percent reduction in infection for those who got the drug. The reduction was 54 percent among those who reported using it at least 80 percent of the times they had sex.
The microbicide gel also had a significant protective effect against transmission of genital herpes.
Scientists have long struggled to create a product that women could use without the consent or even the knowledge of their partners. In South Africa and many other countries, "women can end up in a violent situation if they ask men to use a condom," said Drexel's Welles. "This changes the whole dialogue about women being able to protect themselves."
Further testing may dramatically improve the gel's effectiveness as the proper dosage and timing become clearer, said Harvard immunologist Judy Lieberman. "There's a lot of room for improvement."
And the encouraging results for the tenofovir gel may also open the door to other protective measures, said Lieberman, who, like Welles, was not involved with the study.
Tenofovir, which is also known as Viread when given as part of an antiretroviral drug cocktail, works by disabling a protein that the HIV virus needs to replicate itself. Lieberman has formulated a protective gel using a different strategy, called RNA interference - essentially attacking the genetic material of the virus.
Though she's gotten promising results in the lab against both HIV and herpes, she said that when she tried to move forward with clinical trials, the costly next step, she heard nothing but skepticism from venture capitalists, biotech companies, and big pharma. They thought it was too unlikely to work, she said, and had grown skittish after the numerous failures of seemingly promising HIV vaccines.
That may finally begin to change.
Contact staff writer Faye Flam at 215-854-4977 or fflam@phillynews.com.
