Important note: Information in this article was accurate in 1999. The state of the art may have changed since the publication date.
The Associated Press - Tuesday, Sept. 21, 1999
Brenda C. Coleman, AP Medical Writer
"Resistance is slowly increasing," said Dr. Roger J. Pomerantz, an expert not involved with either study, "If you were looking at this five years ago, you would see zero."
The studies -- published in Wednesday's Journal of the American Medical Association -- involve mostly gay white men. Resistance, however, may be more prevalent in other groups, such as drug users and their sex partners, researchers said.
About 40,000 new HIV infections occur yearly in the United States. In recent years, powerful drug cocktails have subdued the virus to undetectable levels in many patients. But studies have found the virus persists or comes roaring back in 10 percent to 50 percent.
The complicated drug regimen has proved difficult to adhere to, and many patients who missed doses or quit taking their medicines developed drug-resistant infections that are now being passed along to others.
"I wasn't that surprised. This is what happens in infectious disease," said Pomerantz, director of the Center for Human Virology at Jefferson Medical College in Philadelphia.
HIV is still so new that scientists disagree about even how to define resistance. And since both studies used laboratory tests, no one really knows how the definitions will translate into patient care. Giving high doses of a drug may be enough to overwhelm a virus' resistance, Pomerantz said.
In one study, researchers at the University of California at San Diego defined resistance as a 10-fold increase in HIV's ability to withstand a drug when compared with a laboratory strain. That study, led by Dr. Susan J. Little, tested 141 patients -- in San Diego, Los Angeles, Dallas, Denver and Boston -- and found that three (2 percent) had HIV with at least 10-fold greater resistance to one or more drugs.
An additional 36 patients (26 percent) had HIV that was 2.5 to 10 times more resistant.
In the other study, researchers at Rockefeller University in New York defined resistance as a threefold increase in HIV's ability to withstand a drug. That study, led by Dr. Daniel Boden of the Aaron Diamond AIDS Research Center, tested 80 subjects in New York and Los Angeles. Of 67 in whom resistance could be tested, three (4.5 percent) had HIV that was highly resistant -- fivefold resistant -- to multiple drugs. The subjects were among 18 (26.8 percent) with HIV that was at least threefold resistant to at least one drug.
Testing every newly infected patient for drug resistance would be impractical because the tests cost several thousand dollars and are difficult to interpret, Pomerantz said.
But if a patient takes a drug cocktail faithfully and it isn't working, testing should be considered to see how the combination of medicines might be reformulated, he said.
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