Effect of number of medications on cardiovascular therapy adherence

OBJECTIVE: Increasing regimen complexity is generally assumed to result in lower medication adherence, but there is conflicting evidence. This study determined the relationship between the number of medications dispensed and adherence with chronic cardiovascular regimens. METHODS: A survey was administered to 367 patients who had taken an angiotensin-converting enzyme inhibitor or lipid-lowering medication for at least 3 consecutive months. Information was collected on nonprescription drug use, demographics, adverse effects, and use of adherence aids. Prescription drug use data over the previous 12 months were obtained for each subject from the British Columbia prescription claims database. Adherence for each prescription medication was calculated based on prescription fill dates and number of days supplied. Univariate and multivariate analyses were used to identify predictors of nonadherence (<80%) with cardiovascular medications. RESULTS: Forty-five subjects (12%) were categorized as nonadherent. Nonadherent subjects took fewer regularly scheduled prescription medications per day (4.1 +/- 2.7 vs. 5.9 +/- 3.4; p = 0.001), fewer pills per day (5.3 +/- 3.6 vs. 9.2 +/- 7.1; p < 0.001), and had fewer administration times per day (1.8 +/- 0.7 vs. 2.4 +/- 0.9; p = 0.001). A multivariate logistic regression model adjusting for age, gender, reported adverse effects, reported nonprescription drug use, and use of adherence aids identified fewer regularly scheduled prescription drugs as an independent predictor of nonadherence with chronic cardiovascular medications (OR = 0.85 per medication, 95% Cl 0.74 to 0.94; p = 0.01). CONCLUSIONS: Contrary to popular belief, taking fewer medications was associated with lower adherence with chronic cardiovascular regimens.