Predictors of antihypertensive medication adherence in two urban health-care systems

Most studies on patient-related predictors of adherence used self-reported measures or pharmacy databases to measure adherence. We identified predictors of antihypertensive medication adherence measured by Medication Event Monitoring System (MEMS), the gold standard for adherence assessment, in uncontrolled, predominantly African-American (AA) hypertensives from large urban public and private primary care clinics.

As part of the baseline data collection of a cluster-randomized trial for hypertension control, we measured adherence in a random sample of 124 participants using MEMS caps. We also included the data of 52 patients in intervention clinics who subsequently completed MEMS monitoring on referral from their provider. Participants were classified as adherent if they took ≥ 80% of all prescribed doses. Multivariate logistic regression was used to predict adherence.

Of 176 patients monitored, 61 (34.6%) took <80% of prescribed doses. AA ethnicity (odds ratio (OR) AA vs. Hispanic = 0.36; 95% confidence interval (CI) 0.15-0.86), female sex (OR = 0.38; 95% CI 0.15-0.91), and public clinics as source of care (OR public clinics vs. private clinics = 0.45; 95% CI 0.20-0.97) were independently associated with lower adherence. Higher adherence was seen in patients monitored by clinician order in the intervention clinics (OR intervention sample vs. random baseline sample = 2.15; 95% CI 0.96-4.81) and diabetic patients (OR = 2.05; 95% CI 1.01-4.15). All analyses were adjusted for education, employment status, and other potentially confounding factors.

AA ethnicity, female gender and attending a publicly funded primary care clinic were associated with lower adherence. Whether targeting these groups for special interventions would improve overall adherence needs further study.