THURSDAY, June 19 (HealthDay News) -- The herpes drug aciclovir (Zovirax) doesn't reduce the risk of HIV-1 infection in people who have sex with men infected with genital herpes, a U.S. study finds.

Previous research has shown that herpes simplex virus type-2 (HSV-2) infection -- the most common cause of genital herpes -- increases the risk for HIV-1 infection by two- to threefold.

In this new, randomized, placebo-controlled phase III study, Dr. Connie Celum, of the University of Washington in Seattle, and colleagues examined whether aciclovir, an antiviral drug commonly used to help suppress genital herpes, would reduce the risk of HIV-1 infection.

The final analysis included almost 1,400 HIV-negative but HSV-2 positive women in Africa and more than 1,800 American and Peruvian men who have sex with men. Of those participants, almost 1,600 received 400 milligrams of aciclovir and a similar number received a placebo, for 12 to 18 months.

The incidence of HIV-1 infection was 3.9 per 100 person years in the aciclovir group and 3.3 per 100 in the placebo group -- not a significant difference, the researchers reported in the June 21 edition of The Lancet. In the aciclovir group, incidence of genital ulcers was reduced by 47 percent, and incidence of genital ulcers caused by HSV-2 was reduced by 63 percent.

"Our results show that suppressive therapy with standard doses of aciclovir is not effective in reduction of HIV-1 acquisition in HSV-2 seropositive women and MSM (men who have sex with men). Novel strategies are needed to interrupt interactions between HSV-2 and HIV-1," the researchers concluded.

Further research is needed to determine why aciclovir doesn't reduce the risk of HIV infection, they added.

These findings and others raise doubts about whether control of sexually-transmitted infections should be promoted specifically for HIV prevention in HIV-negative populations, Professor Ronald Gray and Professor Maria Weaver, of Johns Hopkins University, wrote in an accompanying editorial.

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