A Prospective Study of Predictors of Adherence to Combination Antiretroviral Medication

Abstract

OBJECTIVE: Adherence to complex antiretroviral therapy (ART) is critical for HIV treatment but difficult to achieve. The development of interventions to improve adherence requires detailed information regarding barriers to adherence. However, short follow-up and inadequate adherence measures have hampered such determinations. We sought to assess predictors of long-term (up to 1 year) adherence to newly initiated combination ART using an accurate, objective adherence measure. DESIGN:A prospective cohort study of 140 HIV-infected patients at a county hospital HIV clinic during the year following initiation of a new highly active ART regimen. MEASURES AND MAIN RESULTS:We measured adherence every 4 weeks, computing a composite score from electronic medication bottle caps, pill count and self-report. We evaluated patient demographic, biomedical, and psychosocial characteristics, features of the regimen, and relationship with one's HIV provider as predictors of adherence over 48 weeks. On average, subjects took 71% of prescribed doses with over 95% of patients achieving suboptimal (<95%) adherence. In multivariate analyses, African-American ethnicity, lower income and education, alcohol use, higher dose frequency, and fewer adherence aids (e.g., pillboxes, timers) were independently associated with worse adherence. After adjusting for demographic and clinical factors, those actively using drugs took 59% of doses versus 72% for nonusers, and those drinking alcohol took 66% of doses versus 74% for nondrinkers. Patients with more antiretroviral doses per day adhered less well. Participants using no adherence aids took 68% of doses versus 76% for those in the upper quartile of number of adherence aids used.CONCLUSIONS: Nearly all patients' adherence levels were suboptimal, demonstrating the critical need for programs to assist patients with medication taking. Interventions that assess and treat substance abuse and incorporate adherence aids may be particularly helpful and warrant further study. Unfortunately, many reports have been limited by a cross-sectional design, the use of self-report measures or both. 7,13,30±48 Several studies assessed only patients' selfreported reasons for nonadherence, rather than testing for associations between these factors and actual adherence. 36,37,45,47,48 We designed a longitudinal, cohort study to address some of the unresolved questions related to the influence of various factors on adherence to ART. We prospectively measured hypothesized predictors of ART adherence and followed patients for a prolonged period of time (up to 48 weeks). Then we used a carefully constructed measure of adherence that has been shown to be significantly predictive of virologic outcomes. 21 We derived the following hypotheses from the existing literature and tested them in this study: greater self-efficacy toward adherence,