Washington

High rates of drug resistance are causing infectious-disease experts to recommend that doctors change the way they use medications against HIV.

A study released on 16 July by Charles Boucher, a virologist at Utrecht University in the Netherlands, at a meeting in Paris of the International AIDS Society (IAS), found that 10% of Europeans newly infected with HIV carry a strain that is resistant to medication.

The study confirms warnings that HIV drug resistance is on the rise. Last August, for example, a team led by researchers from the University of San Diego found that the number of patients newly infected with HIV in North America who carried resistant virus had jumped from 3.4% in 1995–98 to 12.4% in 1999 and 2000 (S. J. Little et al. N. Engl. J. Med. 347, 385–395; 2002).

The growth of resistance has profound implications for AIDS treatment globally, researchers say. On 14 July, the US Department of Health and Human Services released a set of updated guidelines for anti-retroviral treatments, cautiously recommending for the first time that doctors test for drug resistance in newly infected patients at the outset of treatment, to make sure that the drugs they prescribe will work.

A panel of experts convened by the IAS on 1 July published similar recommendations (M. S. Hirsch et al. Clin. Infect. Dis. 37, 113–128; 2003). The IAS panel said that all patients who have been infected for less than two years before beginning treatment should be tested for drug resistance. Virologists have found that drug-resistant forms of HIV can survive in patients for at least two years, and are still studying whether resistance can last longer than that.

Most doctors use drug-resistance tests only in HIV patients who have had several rounds of drug treatment and stopped responding. This is because the tests cost up to $800 per patient, and are sometimes difficult for clinicians to interpret.

But better tools are becoming available to interpret the tests, and as drug resistance becomes more common, testing will become more cost-effective. One analysis has found that testing costs no more than dosing patients with drugs to prevent infections when resistant strains of HIV are common (M. C. Weinstein et al. Ann. Internal Med. 134, 440–450; 2001).

“If the prevalence of resistance is 10% or 12%, and you know that resistance can persist for some time, the case for early testing is much stronger,” says Dan Kuritzkes, director of AIDS Research at Brigham and Women's Hospital in Boston, Massachusetts, and a member of the IAS panel.

The growing rate of resistance raises worries about the pace of drug discovery. This year, three new AIDS drugs were approved by the US Food and Drug Administration. So far, experts say, they have kept up with drug resistance. But the future is hard to predict.

“What we don't know is whether resistance is still growing or whether it's essentially plateauing,” says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases.

Some health officials are calling for more detailed guidelines on which drugs to use in different patients — especially in poor countries, where treatment is not yet widespread. Observers say it will be difficult to get doctors in these countries to submit to such rules.

“If we're going to implement these rules in Africa, we should also do it in Europe,” says IAS president Joep Lange. But even in rich countries, he says, doctors are used to prescribing drugs they are familiar with. “They don't think there might be alternatives,” he says.