Patterns of adherence to antiretroviral medications: the value of electronic monitoring.

OBJECTIVE: To investigate the patterns of intra-subject (between medication) adherence to antiretroviral therapy. DESIGN: A prospective, observational, 3-month study of adherence to antiretroviral therapy at an inner-city clinic in 40 HIV-infected subjects. METHODS: Adherence was monitored monthly by the use of medication event monitoring system (Aprex) caps placed on each antiretroviral drug in a subject's regimen. Agreement between different drug classes and dosing schedules, for each subject, was quantified by estimating the mean difference in adherence, with 95% limits of agreement. An analysis of variance model was used to estimate the variance of the differences. Individual dosing calendars were examined for each subject. RESULTS: The dosing schedule was a strong predictor of intra-subject adherence. Regardless of the subject's overall adherence rate, high or low, when subjects missed a dose of one medication, they missed a dose of both medications taken at that dosing time. Conversely, when medications were scheduled to be taken together, regardless of the drug class, the medications were taken at the same times. The majority of the subjects took medications at obviously incorrect times. Problematical adherence was related to thrice-daily dosing and food restrictions. CONCLUSION: This is the first report objectively to quantify intra-subject adherence to antiretroviral therapy and report the findings in detail. We observed clear patterns of drug-taking behavior among the subjects in our study. To the extent that medication scheduling is a controllable factor, our report provides an insight into specific patterns of behavior that may be targets for adherence counseling.