NEW YORK, Mar 20 (Reuters Health) - One of the biggest obstacles in treating HIV is the virus's ability to mutate into drug-resistant forms. But there is growing evidence that testing patients for viral resistance before they start a new drug regimen may help doctors choose the best treatment for individual patients. Now new findings suggest this expensive testing makes sense in terms of healthcare dollars as well.

Although the powerful drug combinations known as highly active antiretroviral therapy (HAART) are keeping many HIV-positive people alive longer, patients still face the threat of developing resistance to one or more drugs in their regimens. Right now, some patients undergo drug-resistance testing after they fail on their first treatment regimens so their doctors can weed out the culprit drug and replace it with another. Experts have recommended that such testing become routine.

And according to some researchers, the tests may also predict which drugs will fail a given patient, and could be used to design patients' first drug combinations. A looming question is whether these tests, which range from $400 to $1,000 per test, are worth the cost. They may be, the study authors report in the March 20th issue of the Annals of Internal Medicine.

Using a computer model, researchers led by Dr. Milton C. Weinstein of Harvard University in Boston, Massachusetts, concluded that one type of drug-resistance testing was "cost-effective" in picking patients' second or first drug regimens. The cost of testing patients before they had failed a drug regimen was heftier, but it may become more cost-effective as viral resistance grows more common, the report indicates.

Weinstein's team used data from clinical trials of HIV patients to create their cost-benefit model. The investigators found that drug-resistance testing would bring patients a gain in quality years of life that outweigh the tests' price. Preventing drug resistance would presumably keep patients healthier and out of the hospital for longer periods of time.

In an editorial accompanying the report, Dr. Michael S. Saag of the University of Alabama at Birmingham, writes that the "optimal use of resistance testing has not yet been fully defined."

According to Saag, most experts agree that testing makes sense for patients who have failed their drug regimens and for pregnant women to ensure they get the "best" regimen. But whether it should be used to predict viral resistance and design patients' first regimens depends on how common viral resistance is in the community, he writes.

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