WASHINGTON Men who took Truvada, a once-a-day pill combining two Gilead Sciences Inc HIV drugs, markedly reduced their risk of becoming infected with the AIDS virus, researchers reported on Tuesday.
On average, the 1,200 or so men who took the drug had a 44 percent lower rate of HIV infection than men given a placebo, and the men who took the pill every day or almost every day had a 70 percent lower risk, the researchers reported in the New England Journal of Medicine.
Here are some questions and answers about the trial:
HOW DID THE PILLS PROTECT THE MEN?
The pills contain two Gilead drugs called tenofovir and emtricitabine, which are used as part of three-drug cocktails to treat AIDS infections. Both are in a class called reverse transcriptase inhibitors, which interfere with the ability of the virus to replicate in cells.
The approach is called pre-exposure prophylaxis, or Prep for short.
WON'T THIS ENCOURAGE RISKY SEXUAL ACTIVITY?
This is one of the factors that the researchers worried about, but the trial showed the men were more, not less, likely to use condoms. To take part in the trial, the gay, transgender and bisexual men had to attend regular clinics where they got HIV counseling, tests and treatment for other sexually transmitted diseases and hepatitis.
"Many had never had HIV testing or counseling before, yet they were attracted," Dr. Robert Grant of the Gladstone Institutes and the University of California San Francisco, who led the study, said in a telephone interview. "The Prep concept will, we think, attract the highest-risk people."
Public health agencies stress that consistent condom use and reducing the number of sexual partners remain the most effective ways for gay and bisexual men to protect against HIV infection.
"The findings don't mean using the pill instead of condoms. But the pill is a very powerful backup," Grant said.
WILL ANY HIV DRUG WORK?
"Emtricitabine and tenofovir have several characteristics that are particularly valuable for prevention," Grant said. "They have very long half-lives, so you can take them once daily." Other HIV drugs must be taken twice a day.
They are safe, cause few side-effects, and do not interact with other drugs.
More than 20 AIDS drugs are now on the market and can be combined in various ways to control the virus in infected people. Drugmakers include GlaxoSmithKline, Pfizer, Bristol-Myers Squibb and Abbott Laboratories.
DIDN'T WE ALREADY HEAR SOMETHING ABOUT AIDS DRUGS REDUCING
In February U.S. researchers reported that people across Africa who took AIDS drugs cocktails were 92 percent less likely to infect their partners with the virus, and followed up with details of their findings throughout the year.
Last December, U.S. officials had to change direction on a Prep trial in Botswana because too few people were being infected. Tuesday's trial showed results because the men taking part were at very high risk of infection.
Researchers are also testing microbicides -- gels or creams that help prevent sexual transmission of the virus.
In July, researchers said a gel containing tenofovir reduced HIV infections in women by 39 percent over two and a half years in a trial in South Africa.
Another trial called the VOICE study is examining three different, once-daily HIV prevention strategies in women: a combination pill, a pill containing only tenofovir, and a tenofovir-based vaginal gel in African women. Results are expected in 2013.
WHAT ABOUT LONG-TERM EFFECTS?
The National Institute of Allergy and Infectious Diseases will continue to offer all 2,499 men in the Prep trial a chance to keep taking Truvada.
They want to see if the men develop what is known as resistance, when a drug loses its effectiveness against an infection.
They are also looking for long-term side-effects. Truvada so far causes at worst mild nausea and headaches but other HIV drugs can damage the blood vessels and heart and cause strange changes in body fat distribution called lipodystrophy.
Grant notes that many people take daily medication, sometimes for life, to ward off disease -- malaria, for instance but also drugs to lower cholesterol and blood pressure. Women also take hormones to prevent pregnancy.