Copayment level and compliance with antihypertensive medication: analysis and policy implications for managed care.

OBJECTIVE: To measure the impact of medication copayment level and other predictors on compliance with antihypertensive medications, as measured by the medication possession ratio. STUDY
DESIGN: Retrospective observational analysis.
METHODS: We used claims data from a large managed care organization. The identification of subjects was based on a diagnosis of hypertension and a filled prescription for antihypertensive medication between January 1999 and June 2004. Multivariate logistic regression models were used to evaluate copayment level and patient characteristics as predictors of medication compliance.
RESULTS: Analysis of data for 114,232 patients filling prescriptions for antihypertensive medications revealed that compliance was lower for drugs in less preferred tiers. Relative to medications with a 5 dollars copayment, the odds ratio (95% confidence interval) for compliance with drugs having a 20 dollars copayment was 0.76 (0.75, 0.78); for drugs requiring a 20 dollars to 165 dollars copayment, the odds ratio for compliance was 0.48 (0.47, 0.49). Medication compliance also differed by patient age, morbidity level, and ethnicity, as well as by medication therapeutic class--with the best compliance observed for angiotensin receptor blockers, followed by calcium channel blockers, beta-adrenergic receptor antagonists (beta-blockers), angiotensin-converting enzyme inhibitors, and last, thiazide diuretics.
CONCLUSIONS: Copayment level, independent of other determinants, was found to be a strong predictor of compliance with antihypertensive medications, with greater compliance seen among patients filing pharmacy claims for drugs that required lower copayments. This finding suggests that patient use is sensitive to price. The potential impact on compliance should be considered when making pricing and policy decisions.