Doctors are finding new uses for HIV drugs, with one study showing they might safely protect women at high risk of infection and a second showing that people can safely skip the most toxic pills.
Research to be presented at the 16th International Conference on AIDS, which opens on Monday, shows new benefits from drugs that help suppress the fatal and incurable virus.
The human immunodeficiency virus that causes AIDS infects close to 39 million people globally.
Since the virus started spreading globally in the 1980s it has killed 25 million people and orphaned millions more.
There is no vaccine and no cure.
Only condoms and complete sexual abstinence have been shown to prevent infection.
Family Health International tested an experimental approach called pre-exposure prophylaxis or PrEP using a drug called tenofovir.
Researchers believe the drug, made by the California-based Gilead Sciences Inc under the brand name Viread, could keep healthy people from getting HIV.
The researchers gave either the pill or a placebo to 936 high-risk women in Cameroon, Ghana and Nigeria.
They were not able to tell if the pills actually prevented infection with the AIDS virus but tested the women's kidney and liver function to make sure taking the drugs was safe.
They also wanted to see if the women would take the drugs consistently.
"The encouraging news was in regard to safety, acceptability and risk," Ward Cates, who helped lead the study, said in a telephone interview.
One worry was that the women would feel protected by the drug and would fail to use condoms, or have sex more often. But this did not happen during the trial, Cate said.
The women, all recruited because they were sex workers, or had sex frequently with different men, all got counselling and condoms at every visit.
Several women got pregnant - at a rate of about 40 per 100 women per year - suggesting that the women did not always use condoms, Cate noted.
"In general, access to condoms is limited in many of these resource-poor settings," Cates said.
"This approach is not intended for people who are in the general population but only for people in very high-risk settings for whom no other HIV prevention approach is available."
In some countries, HIV drug cocktails can keep patients healthy. There are more than 20 drugs available now and it is not always clear which combination is best. Some drugs cause more side-effects than others.
A team led by Dr Sharon Riddler of the University of Pittsburgh School of Medicine at the University of Pittsburgh tested some of the combinations to see if patients could skip the oldest class of HIV medications, called nucleoside reverse transcriptase inhibitors, also known as NRTIs or "nukes".
They can cause intolerable side effects in some patients, ranging from diarrhoea to hepatitis.
Their test of 753 volunteers at 55 centres showed that using two drugs in the NRTI class with a drug called efavirenz, a non-nucleoside reverse transcriptase inhibitor, suppressed the virus in more people than a more widely used combination.
"Now that we've completed the trial, there should be little doubt that patients can benefit from this 'nuke'-sparing treatment regimen when NRTI side effects are a problem," Ridley said in a statement.
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