New method measures adherence to HIV drug prescriptions

CHAPEL HILL - Researchers have developed a more accurate way to determine how well people with HIV are sticking to their drug regimens.

The new method involves a combination of measures, including a dated record made by an electronic pill bottle cap.

The study appears May 15 in the Annals of Internal Medicine. The findings clearly show higher blood levels of HIV among patients who failed to take their antiretroviral regimen as prescribed.

"AIDS cases and deaths have dropped dramatically since new drug cocktails came on the market in the late 1990s," said Carol Golin, MD, research assistant professor of general medicine at UNC-CH School of Medicine and research associate with the UNC Cecil G. Sheps Center for Health Services Research. "But if patients aren't taking their medications all the time the virus can mutate and become resistant, and then the drugs don't work. In addition, that resistant virus can be transmitted to another person. Then that person would acquire a virus that's resistant to those drugs from the start."

The new study revealed that after taking antiretroviral drugs for six months, people with undetectable levels of HIV were taking their medication as prescribed about 85 percent of the time. But those with detectable virus blood levels were taking their pills about 66 percent of the time.

Compared to patients on other chronic medications, that's a relatively high adherence rate, according to study co-author Andrew Kaplan, MD, associate professor of medicine at UNC-CH.

"When you look at patients with high blood pressure, they typically take their medication 40 to 50 percent of the time," Kaplan said. He noted that it is difficult to get patients to take any kind of medication regularly.

Moreover, noted Kaplan, patients may take anywhere from six to 30 pills a day and may experience "a potpourri of side effects" including nausea, vomiting, headaches, rashes, and kidney stones.

"These are complex [antiretroviral] regimens, they have side effects, and they are chronic--people have to take them for life," said Golin.

In their report, the authors pointed to several limitations in measuring adherence to drug regimens. They noted that measures of drug levels in blood or urine "provide only a snapshot of behavior, are largely impractical in clinical venues and are affected by factors other than adherence." In addition, counting the pills in a patient's prescription bottle is time consuming, and patients may just throw away pills they haven't taken.

Golin and her collaborators at UNC and UCLA followed 108 HIV patients for one year. Once a month they checked medication adherence three ways. They counted the number of pills remaining in the patients' medicine bottles. They asked patients how well they had followed the regimen.

But the "backbone" of the study, Golin said, was an electronic pill bottle cap called MEMS, for Medication Event Monitoring System. "MEMS records the exact time and date every time the pill bottle is opened. Each method had shortcomings, but MEMS was the most objective way to measure adherence," she said.

The researchers used the three measures to generate a Combined Adherence Score, CAS. The CAS was both more sensitive and more specific than any of the measures used alone. In other words, it was the best at spotting people who were not taking their medication, and also at distinguishing those who were from those who were not.

Because of the amount of information that needs to be collected, most health clinics probably wouldn't use the CAS, Golin said. "But for research purposes, particularly where you want to link this behavior to reductions in the amount of virus in a patient's blood, it's really critical that you measure adherence as accurately as possible. And this gives people a new way of doing that that's not been done before."

Support for this study came from the National Institute of Allergy and Infectious Diseases, National Institutes of Health.

By Steven Baragona
UNC-CH School of Medicine

media note: Contact Dr. Golin at 919-966-7939; [email protected]. Contact Dr. Kaplan at 919-966-2536.
School of Medicine contact: Leslie Lang, 919-843-9687; [email protected]