The result is hailed as the first major AIDS-prevention breakthrough.
Research was conducted on 2,500 high-risk gay men, but experts
believe further study will show effectiveness in other groups.
In a finding that is being widely hailed as the first major
prevention breakthrough in the AIDS era, researchers have shown
that taking a single daily pill containing two HIV drugs can
reduce risk of contracting the virus by an average of 44% -- and
by more than 70% if the subjects take most of their pills.
The study involved nearly 2,500 high-risk gay men, but experts
hope that the results will be applicable to other populations
considered at risk for contracting the virus. Several studies are
already underway to determine if that is the case.
The findings, reported online Tuesday in the New England Journal
of Medicine, come only a few months after an African study showed
that a microbicidal gel can help protect women from contracting
the virus and a little more than a year after a vaccine trial
suggested that it may eventually be possible to raise antibodies
against the virus.
"To see all these prevention strategies come together, we can
begin to see an end to the epidemic," said A. Cornelius Baker of
the Presidential Advisory Council on HIV/AIDS. "The National AIDS
Strategy introduced by the president in July called for reducing
the U.S. epidemic by 25%. ... If we can prove this works and get
this strategy into the communities, we can reach that goal much
quicker than we had anticipated and move even further to more
Dr. Anthony S. Fauci, director of the National Institute of
Allergy and Infectious Diseases, which was the major sponsor of
the study, cautioned, however, that "No single prevention
strategy is going to be effective for everyone, and it is
important to note that the new findings pertain only to ... men who
have sex with men."
Experts agreed, however, that there is no reason to think that it
would not be successful in other groups, although it must be
The new strategy is called pre-exposure prophylaxis, and that is
an approach that has been used successfully in certain other
diseases. Malaria or tuberculosis drugs, for example, are
frequently prescribed to people entering areas with high
transmission rates. Antiretroviral drugs are also used to prevent
transmission of HIV from mothers to infants during and after
birth and in an effort to prevent infection after accidental
exposure in hospitals and laboratories.
The new study, called iPrEx, was conducted by an international
team headed by Dr. Robert M. Grant of the Gladstone Institute of
Virology and Immunology at UC San Francisco and Dr. Javier R.
Lama of Investigaciones Medicas en Salud in Lima, Peru. They
enrolled 2,499 men and transgender women who have sex with men at
11 sites in six countries.
Half were given a daily dose of Truvada, a pill containing the
AIDS drugs emtricitabine and tenofovir, and half a placebo.
Truvada was chosen because it is effective, has few side effects
and is already used by more than 1.5 million people worldwide.
Subjects were followed for an average of 14 months, and given
counseling about using condoms and safe sex practices.
The researchers observed 36 HIV infections in the group taking
Truvada, compared to 64 in the control group taking placebo, a
reduction of 43.8%. The reduction in risk, however, was very
sensitive to how regularly the subjects took the medication. For
those who took it on more than 50% of the days, as determined by
pill counts and other measures, the risk fell by 50.2%. For those
who took it 90% or more of the days, the risk fell by 72.8%.
Side effects of the drug were mild, and included nausea in the
first month, small increases in serum creatinine and
unintentional weight loss.
The subjects will be followed for another 18 months to monitor
for long-term effects. In a separate study now underway, the drug
is being tested in women. In separate arms of that study,
researchers are also testing tenofovir only and a gel containing
More information is available at the trial's official website: