HIV is fighting back. Drug-resistant strains now account for a tenth of new infections in North America, and the proportion is rising rapidly.
Although almost all patients with these resistant strains still respond to antiviral drug cocktails, they respond more slowly, emphasising the need to develop new drugs to combat resistance. The author of the study, Douglas Richman of the University of California, San Diego, also thinks all newly infected patients should be screened for resistance, so they can get the most effective treatment right from the start, although not all experts agree.
Antiviral drugs are the only effective weapon against AIDS. Their powers have been hailed as miraculous. Potent drug cocktails have pulled patients back from the brink of death, extended lives and improved the health of many.
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But this success hasn鈥檛 been unqualified. The vast majority of HIV-positive people cannot afford the treatments, and those who do take them often suffer unpleasant side effects. To make things worse, drug-resistant strains of HIV are becoming more common around the world. In a study released last year, for example, Richman鈥檚 team found that more than three-quarters of people being treated for HIV have resistant strains.
But since these patients were already on drug therapy, it wasn鈥檛 possible to tell if they had been infected with resistant strains or if resistance had evolved while they were on the drugs. The latest study looked at 377 people in Canada and the US who had recently been infected with HIV, and had not yet started drug treatment. The team tested viruses from patients for resistance to 15 different HIV drugs, all of which target one of two enzymes.
In samples collected between 1995 and 1998, only 3 per cent of patients harboured resistant viruses, a third of which were resistant to two or more drugs. But over the next two years, the proportion jumped dramatically: 12 per cent were resistant, half of which were resistant to more than one drug (The New England Journal of Medicine, vol 347, p 385).
鈥淭his study shows why you can never be developing drugs fast enough against HIV or any microbe you can鈥檛 eradicate,鈥� says Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases. He sees a pressing need for drugs that target different aspects of the virus鈥檚 life cycle, such as Roche鈥檚 T-20, which stops the virus fusing with cells.
But Fauci questions the need for testing for resistance. He points out that such tests aren鈥檛 completely reliable. And even though patients with drug-resistant HIV responded more slowly to drugs, all but one of the 202 people followed had significant viral repression after 24 weeks. 鈥淭herapy, as it is, is still doing very well,鈥� says Fauci.