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Imperfect HIV Drug Use Raises Resistance Risk

Failure to Take Medications as Directed Could Quadruple Drug Resistance Risk

WebMD Health News

Jan. 13, 2005 (New York) -- People infected with HIV who take their medications most but not all of the time may be up to four times more likely to develop drug resistance.

Drug resistance renders even the most effective HIV drugs helpless at controlling the virus.

A major new Canadian study shows that consistent yet imperfect use of a combination of three HIV drugs known as highly active antiretroviral therapy (HAART) more than quadrupled the risk of developing resistance to one or more of the drugs.

"It's pretty good adherence to be picking up 70%, 80%, or 90% of your prescriptions, but doing that is actually putting you at the highest risk of picking up drug resistance," says researcher P. Richard Harrigan, PhD, director of the British Columbia Centre for Excellence in HIV Research Labs in Vancouver, Canada.

"It's not like in horseshoes where close is good enough. Close is probably a bad thing in terms of drug resistance," says Harrigan.

In contrast, people who took their HAART medications as directed 95% or more of the time had a much lower risk developing drug resistance and were more likely to have very low blood levels of HIV.

Harrigan presented the results of his study today at an American Medical Association briefing in New York City on the epidemic of HIV drug resistance.

Drug Resistance, the Latest Challenge in HIV Therapy

HAART has drastically reduced the death rate due to HIV/AIDS in the last 10 years, but researchers say resistance to one or more of the drugs used in the three-drug cocktail is an increasingly common problem. Drug resistance now affects more than 50% of people treated for HIV in the U.S.

HIV drug resistance occurs when the virus mutates and decreases the ability of a drug or combination of drugs to prevent replication of the virus in the body.

About 20 drugs from three different classes are currently used in HAART in a variety of combinations, which allows doctors to change the treatment if resistance to one of the drugs occurs.

But resistance to one drug can also decrease the effectiveness of other drugs in the same class and reduce the overall effectiveness of the treatment in the long-term by allowing HIV levels to increase.

HIV Drug Adherence Predicts Resistance

In the study, researchers followed more than 1,100 men and women who began treatment for HIV infection in Alberta, Canada, from 1996-1999 for 2.5 years.

To determine how well the participants followed their prescribed HAART therapy, researchers analyzed prescription refill records as well as checked blood samples to see if the patient had the desired levels of drugs in their system.

During the 2.5-year follow-up period, the study showed that one in four participants developed resistance to one or more of their HIV medications. Among those that developed HIV drug resistance, the average time before drug resistance developed was about eight months.

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