Drugs that treat AIDS may spur prevention pill
TORONTO -- The same drugs that transformed AIDS from a death sentence into a treatable condition a decade ago are now showing promise in preventing infections in the first place.
Researchers on four continents are studying whether AIDS treatment drugs -- taken either daily or before high-risk sex -- might be safe and effective enough to use as a prevention tool. This week, scientists presented the first evidence that otherwise healthy people can take the medication without suffering serious side effects.
With no vaccine on the horizon, scientists at the 16th International AIDS Conference predicted that a prevention pill could prove instrumental in slowing an epidemic that every year spreads to an additional 4 million adults and children around the globe.
That would be pivotal in Africa and Asia, where the virus is most pervasive. Researchers said a prevention drug could be particularly effective in the developing world, where it would allow women to better protect themselves, rather than having to rely on a man to use a condom.
``There's an enormous need for female-controlled methods," said Dr. Joep Lange, a Dutch HIV specialist. ``And what is more female-controlled than taking a pill in the morning that could protect you?"
Prevention specialists envision the drug being used by different patients in different ways. Some, such as prostitutes, might take it all the time. Others, with a more episodic risk, would take the pill before engaging in dangerous behavior.
But the research has been clouded by controversy.
In Cambodia, for example, a study of prostitutes was halted after activists accused researchers of withholding information on other prevention methods, so they would have more infected women to study.
Researchers said they had provided the women extensive counseling on how to protect themselves.
There have also been warnings from AIDS specialists, who question the soundness of using a treatment medication for prevention.
They are concerned that if someone becomes HIV-positive while taking the pill, the virus could outwit the drug and become resistant to it -- potentially rendering the drug useless as a treatment.
In many respects, the hunt for a prevention pill embodies the hopes and frustration of all AIDS research. Such a pill must be powerful, specialists said, but also safe; widely available, but not be misused.
And it must be as available in the developing world as in the West.
The push for a prevention pill and other methods of blocking exposure to HIV also reflects disenchantment by researchers with what is called the ABC approach -- abstinence, ``be faithful," and condoms -- which is championed by the Bush administration.
``I would like to believe HIV prevention will be more than ABC," South African researcher Gita Ramjee said at the conference to sustained applause.
Enthusiasm for a prevention pill extends beyond the scientific community, with figures such as Bill Gates and Bill Clinton championing the cause.
``Oral prevention has not gone as fast as it should," said Gates, whose foundation has underwritten some of the experiments. ``We blame ourselves for not pushing that more."
This week, researchers presented study results showing that an HIV prevention pill is safe.
Scientists from Family
They found that the women who received a tenofovir pill every day, and were tracked for, on average, six months, were no more likely to suffer medical complications than those who got a placebo.
For both prevention and treatment, the pill works by stopping the virus from becoming established once it enters a human cell. The drug was chosen for prevention experiments because it had proved potent and safe in AIDS patients, and because earlier studies on monkeys showed it prevented infection.
But the human study failed to determine whether the drug actually prevented the women from becoming infected with HIV.
There were so few infections among either group in the study that researchers could reach no conclusions about its effectiveness, said Leigh Peterson, the scientist who directed the study.
A total of only eight women became infected, six who had received placebos and two who received the drug.
Peterson said she had expected about 30 of the women to contract AIDS, but said that after counseling, women in the study tended to engage in safer sex practices, and therefore became less likely to contract the virus.
And, while encouraging, the initial report on whether the five-year-old drug is safe for healthy people doesn't answer whether the prevention pill would continue to be free of side effects if used for years.
``We don't know what it will look like if you take 10 years of tenofovir," said Lange, the Dutch researcher. ``We simply don't know."
Further tests are being performed to see if -- in the two women who became infected while on tenofovir -- the virus showed any signs of developing resistance to the drug.
A specialist from Massachusetts General Hospital, Dr. Rochelle P. Walensky, said the issue of resistance looms large over development of a prevention pill, because patients with resistant virus would lose tenofovir as a potential treatment option.
There are about 25 AIDS drugs today, and patients typically take a cocktail of three of them.
``It becomes a matter of a trade-off," said Walensky. ``How much resistance would you be willing to accept if this drug could work in preventing transmission?"
At least $54 million is being spent on prevention-pill experiments globally.
But in nine trials in various stages of completion, only one drug other than tenofovir is being used. Researchers said more drugs must be studied to find the best prevention pill.
Lange and other researchers said drug companies historically have been leery of providing their pills for prevention studies.
They reason that while it is one thing to give a powerful medication to someone who is sick and willing to accept side effects, the equation is different for a person who is healthy.
The biggest study involves 1,600 intravenous drug users in Thailand.
But a prominent Thai AIDS activist said that even if that study and others show the medicine is both safe and effective, there's no guarantee it will get into the hands of people at greatest risk of being exposed to the virus.
Nimit Tienudom, a leader of a Thai foundation that helps get drugs to AIDS patients, wondered who would pay for prevention pills.
``When we are talking in Toronto or the US," he said, the 57-cent-cost per pill ``is very cheap."
``But for Thai people," Tienudom said, ``that is not cheap."
Stephen Smith can be reached at stsmith@globe.com. 
