Postexposure HIV Protection

A gel that can be applied up to three hours after sexual activity could protect women against HIV infection, new research has shown...

HIV, the agent that causes AIDS, remains the worst pandemic yet faced by humans. Globally, millions are infected and the daily death toll is in the thousands.

So far it has not been possible to produce an effective vaccine against the virus. Until this happens, researchers have been exploring other interventions that can block transmission of the disease.

Amongst men, circumcision has been shown to be powerfully protective, reducing the risk of picking up the infection by 60-80%.

In women, anti-HIV-drug-impregnated genital creams and gels designed to be applied prior to engaging in sexual activity have also shown modest benefits, reducing disease risk by about 40%.

But the use of these products requires the woman to anticipate when sexual activity might be about to take place, and relies on her partner cooperating. Also, the HIV-blocking drugs that have been used in these gels are agents that target only the earliest part of the virus lifecycle, precluding the use of these products as preventatives once a person has potentially been exposed.

Now US scientists have successfully tested a new gel formulation containing an already-licensed drug called raltegravir, which targets a much later stage of the virus replication cycle, known as integration, meaning that the product can be used effectively to provide post-exposure protection for up to 3 hours after intercourse.

So far, the new product has been piloted on monkeys that were challenged with a virus called SHIV (simian HIV), the macaque-equivalent - and a close relative of - the human AIDS virus.

Administered up to 3 hours after genital exposure to SHIV, the raltegravir gel prevented infection in four out of five subjects, a performance twice as good as that achieved by the existing generation of genital gels available for human use. Four monkeys treated with a placebo gel all became infected.

Writing in Science Translational Medicine, US Centers for Disease Control and Prevention researcher Charles Dobard and his colleagues were also able to show that, even where infection did take place, the use of the drug-laced gel was not associated with any signs of viral resistance to the agent.

"We provide proof of concept that topically-applied integrase inhibitors protect against vaginal SHIV infection when administered shortly before or 3 hours after virus exposure."