SAN FRANCISCO — Adherence to highly active antiretroviral therapy remains important, even though treatment may be more forgiving of nonadherence than some have suggested, Dr. Kristen M. Ries said at a meeting on HIV management sponsored by the University of California, San Francisco.
In 1999, adherence to a HAART regimen was said to require 95% compliance, or else the patient's infection was likely to become resistant to treatment. That figure is still quoted today.
But the situation is probably not that simple. The study that produced the 95% figure used data from patients who were taking a single protease inhibitor or had taken many nonnucleoside reverse transcriptase inhibitors, not from those on HAART, said Dr. Ries, clinical director of the infectious diseases and HIV clinics at the University of Utah Hospital, Salt Lake City.
Rates of resistance and treatment failure actually vary somewhat depending on the regimen and the particular drugs used, she said.
In general, it has been estimated that for every 10% decrease in adherence there is a doubling of the viral load and a 20% increase in disease progression, and Dr. Ries thinks “that is generally true.” But patients are individuals and so are the drugs.
According to current data, a single protease inhibitor selects for resistance at about 85% adherence. A nonnucleoside reverse transcriptase inhibitor is more forgiving of individual missed doses, but nonadherence is more likely to result in viral mutations that will render the entire class ineffective.
“Nonadherence is still more predictive of treatment failure than almost everything else, at least in my hands,” she said, adding that physicians who treat HIV patients should consider these individual drug characteristics when prescribing a regimen.
Adherence to a HAART regimen is difficult because the regimens are complicated, and studies show that many patients on chronic medications are not adequately adherent, Dr. Ries said.
One way to improve patient adherence is to get to know the patient before prescribing, so that knowledge can be applied to choosing a regimen. It also helps to educate the patient before he or she starts therapy, because a patient who does not trust a regimen or is not committed will be less adherent, she advised.
Another approach is to always ask the patient about adherence using specific questions, such as: “How many doses did you miss last week?” Most patients will admit missing doses if asked in a nonjudgmental manner, but are unlikely to volunteer the information.
Nonadherence “is really chronic relapsing behavior, and it goes on and on,” she added. “There's no way to predict adherence until you actually do it.”