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HIV & AIDS Health Center

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Imperfect HIV Drug Use Raises Resistance Risk

Failure to Take Medications as Directed Could Quadruple Drug Resistance Risk

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.

The two biggest factors associated with drug resistance were inconsistent medication use and a high HIV level in the blood at the start of the study, which is the result of starting treatment later in the course of the disease.

Researchers found that HIV patients who took 80% of their medications were four times more likely to develop drug resistance than those who rarely picked up their HAART prescriptions.

"If you don't pick up any of your prescriptions, you're not very likely to pick up drug resistance," says Harrigan. "But that's not where you want to be in terms of your health because patients with lower adherence had a lower likelihood of actually surviving."

The study showed that the risk of developing drug resistance was highest among people who took their drugs as prescribed 70%-90% of the time.

Those who were near perfect in refilling their prescriptions (greater than 95% refill rate) and actually took them as directed according to blood tests had a fourfold lower risk of developing drug resistance compared to inconsistent HAART users.

Researchers say this group likely avoided drug resistance by effectively suppressing HIV to nearly undetectable levels, which dramatically reduces the risk of the virus mutating and becoming resistant to medication.

However, only about 30% of the HIV patients in the study fit into this "near-perfect drug user" category, and researchers point out that this is among a group of Canadian citizens who received their medications and health care free of charge.

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