June 20 (Bloomberg) -- Treating genital herpes with aciclovir, a generic antiviral medication, doesn't reduce patients' risk of being infected with HIV, a study published in The Lancet medical journal found.

Herpes sufferers given the drug were just as likely to catch HIV, the cause of AIDS, as those who didn't take it, researchers led by Connie Celum at the University of Washington in Seattle said. The U.S. National Institutes of Health and GlaxoSmithKline Plc, which sells the medicine as Zovirax, sponsored the trial.

Observational research has shown that people infected with the herpes simplex virus Type 2, or HSV-2, the most common cause of genital herpes, are almost three times more likely to become infected with HIV than those who don't suffer from the disease. Researchers were testing the theory that managing outbreaks of HSV-2, which often lies dormant, might reduce the patients' risk of acquiring HIV.

``Our results show that suppressive therapy with standard doses of aciclovir is not effective in reduction of HIV-1 acquisition,'' Celum said. ``Novel strategies are needed to interrupt interactions between HSV-2 and HIV-1.''

The scientists studied 3,172 men and women in Africa, Peru and the U.S. who either received aciclovir or a placebo. The trial was in the last of the three stages of testing required for regulatory approval.

Aciclovir works by blocking an enzyme that allows the herpes virus to reproduce. This stops it from infecting more cells in the body.

Ulcer Reduction

The incidence of HIV infection was similar in the two groups after as long as 18 months, the study showed. Aciclovir reduced genital ulcers by 47 percent and genital ulcers definitely linked to HSV-2 by 63 percent.

Researchers need to determine why aciclovir failed to reduce HIV acquisition and didn't reduce genital ulcers as much as expected, Celum said. It may be because the drug isn't absorbed well or because it's metabolized too quickly, Celum said.

Along with other evidence, the study shows that it's questionable whether the control of sexually transmitted infections should be promoted specifically for HIV prevention in HIV-negative people, Ronald Gray and Maria Weaver from Johns Hopkins University in Baltimore, said in a comment.

``Thomas Henry Huxley commented that `The great tragedy of science -- the slaying of a beautiful hypothesis by an ugly fact,''' Gray and Weaver said. ``It's time to reassess the hypothesis and to adjust prevention policy accordingly.''

To contact the reporter on this story: Chantal Britt at cbritt@bloomberg.net.

Last Updated: June 19, 2008 19:01 EDT