Final results from 2 studies suggest that taking HIV medicines can also help to prevent the disease in high-risk people. All of the studies were done in Africa. One included 1,219 heterosexual men and women. They were randomly assigned to receive either two antiviral drugs or placebo (fake) pills. The drugs were tenofovir and emtricitabine. People who got the real drugs were 60% less likely to become infected with HIV. The second study involved more than 4,700 heterosexual couples. One partner in each couple was infected with HIV. The non-infected partners took a pill daily. The pills contained the same 2 drugs used in the first study, tenofovir alone, or no medicine (placebo). Infection rates were 67% to 75% lower for those who got the real drugs. A third study included 2,120 women. It did not find a benefit from antiviral drugs. But many women admitted skipping pills often. Early results of the studies had been released. U.S. drug regulators have been asked to approve using tenofovir plus emtricitabine (brand name Truvada) for prevention of HIV infection. The New England Journal of Medicine published the studies online. HealthDay News wrote about them July 11.

By Robert H. Shmerling, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

Can a person avoid HIV infection by taking anti-viral drugs before exposure?

It's an important question. Past studies suggest that some antiviral drugs used to treat HIV may be effective as a preventive treatment for those at high risk of HIV infection. In fact, a group of expert advisers recently recommended that U.S. regulators approve the medicine Truvada for this purpose. Truvada combines the drugs tenofovir and emtricitabine. It is already approved for treatment of HIV infection.

Three new studies continue to explore the potential of antiviral drugs to prevent HIV. They lasted 1 to 2 years. The New England Journal of Medicine published them online this week. Here's what they found:

• The first study included 1,219 heterosexual men and women. They were randomly assigned to receive either pills containing tenofovir and emtricitabine or placebo (fake) pills. Treatment was about 60% effective at preventing HIV infection.
• The second study included more than 4,700 heterosexual couples. One partner in each couple had HIV infection and the other did not. The partner who was not infected was treated with placebo pills, tenofovir or tenofovir with emtricitabine. HIV Infection rates were 67% lower for those who took tenofovir and 75% lower for those who got both drugs.
• The third study involved 2,120 women. It found no benefit for those who took the 2 antiviral medicines compared with placebo pills. But many women in this study were found to have regularly skipped the drug.

Antiviral treatment led to several side effects. They included:

• Reduced bone density (which increases the risk of fractures)
• Nausea and vomiting
• Abnormal results on kidney and liver tests

The two positive studies suggest that antiviral drugs can help prevent the heterosexual spread of HIV. The third study might have been negative mainly because people skipped their medicines.

However, protection was not 100%. Side effects and missed doses were major problems. It's also possible that taking antiviral drugs could provide a false sense of security and encourage risky behavior.

What Changes Can I Make Now?

In these studies, preventive measures included more than just drug treatment. People were also counseled about how HIV is spread. They were encouraged to use other, well known ways to prevent HIV infection, such as the use of condoms. This is a message that could get lost in the rush to prevent infection with drugs.

You can take steps now to reduce your risk of becoming infected with HIV.

• Use condoms.
• Limit how many sex partners you have.
• Have an HIV test before having sex with a new partner. Encourage your partner to do the same. A newly approved home test should make testing easier and more routine.
• Don't use intravenous drugs or share needles.
• Take precautions to avoid needle sticks if you are a health care provider.
• Seek medical care right away if you may have been exposed to HIV. Treatment within 72 hours after an accidental needle stick or high-risk sex can reduce the chances you'll be infected.

The third study described above shows how even people who are carefully selected and taught about the need to take medicines precisely as prescribed can fail to stick with a treatment plan.

This is true, of course, for just about any drug. But it's a particularly challenging problem when a medicine is taken to prevent trouble in the future rather than to treat symptoms now. And, of course, side effects can also lead to skipped doses.

If your doctor prescribes a medicine (for HIV or any other condition), try to take it as prescribed. If you have trouble sticking to the schedule, talk to your doctor about the reasons. There may be some simple solutions. For example:

• Make sure you understand how you're supposed to take your medicines.
• Make it part of your routine. Some of my patients take their pills right after they brush their teeth.
• Change how you take your medicines. Taking a medicine with (or without) food or changing the time of day may reduce side effects.
• Use technology. For example, set your cell phone alarm as a reminder to take your medicines.

Let your doctor know if cost is a problem. Your doctor may be able to help by contacting your insurance company. Drug companies may offer free or discounted drugs to those in need. Or your doctor may be able to prescribe a lower-cost drug.

What Can I Expect Looking to the Future?

In the future, it could become common for high risk people to take a medicine each day to prevent HIV infection. It could become common even for people at average risk. Before that happens, I hope we'll have antiviral drugs that are more effective and have fewer side-effects than tenofovir and emtricitabine.

Even if antiviral drugs become a standard preventive treatment, it's still better to prevent exposure to HIV. So you can expect more campaigns that encourage "safe sex" and other non-drug approaches to prevent HIV infection.