A series of studies has dispelled the widespread notion that patients who don't take every dose of their anti-HIV medication create a public-health risk by helping to nurture HIV strains that resist therapy.

The findings suggest instead that some patients who do not take all of their medicine are actually less likely to become resistant to therapy than those who adhere rigidly to their doctors' instructions.

This fresh consensus has implications for AIDS-treatment plans in poor countries, where drug companies, in particular, have often argued that HIV patients are less likely to adhere to such instructions than those in rich countries. Such 'low adherence' had been thought to encourage the success of mutations that would make the patients' viruses more resistant to treatment.

"The relationship between adherence and resistance is more complex than we previously understood," says David Bangsberg, a clinician at the University of California, San Francisco, who published a study this week showing that HIV-positive patients who were having trouble subduing the virus were more likely to develop resistance to their medications if they took most of their prescribed doses (D. R. Bangsberg et al. AIDS doi:10.1097/01.aids. 0000076320.42412.fd; 2003).

Bangsberg warns, however, that his and others' findings do not mean that patients should deliberately skip doses, because the data still show that patients who adhere better to their drug regimens live longer. Rather, researchers say, the findings indicate that patients in developing countries should be given access to the most effective drugs early in their treatment, because this maximizes their chances of controlling the virus. Patients who control the virus successfully do not develop drug resistance.

In patients who are taking drugs but are unable to control the virus, the virus is thought to develop mutations that allow it to survive in the presence of the drugs. Such mutants do not survive in patients whose drugs keep the virus in check.

"The clear message is that in the absence of complete viral suppression, the more medication you take, the more resistance you select," says Daniel Kuritzkes, director of AIDS research at Brigham and Women's Hospital in Boston, Massachusetts, and an author of an earlier study that suggested a link between less-effective therapies and resistance (D. R. Kuritzkes et al. J. Acquir. Immune Defic. Syndr. 23, 26-34; 2000).

Researchers also say that data on patients in poor countries show that they are no less likely than those in rich countries to adhere to treatment. "There's no evidence to suggest that adherence is more of a challenge or resistance is more of a problem in the developing world, and there is no reason to delay the roll-out of potent anti-retroviral therapies in resource-poor settings," Kuritzkes says.