Study objective: To measure the association among prescription copayment, drug adherence, and subsequent health outcomes among patients with chronic heart failure (CHF).
Design: Retrospective cohort study.
Data source: Database of a large, national health insurance plan.
Patients: Patients with CHF receiving commercial and Medicare supplemental benefits.
Measurements and main results: We estimated adherence to therapy with beta-blockers or angiotensin-converting enzyme (ACE) inhibitors in 2002 by using the medication possession ratio, an estimate of the proportion of days a patient was exposed to a drug while taking a drug regimen. For 2003, we measured the annualized total cost of health care and identified hospitalizations with a diagnostic code for CHF. We used a two-stage regression approach to model the association among copayment, adherence, and patient outcomes. For patients taking ACE inhibitors, a $10 increase in copayment was associated with a 2.6% decrease in the medication possession ratio (95% confidence interval [CI] 2.0-3.1%). This change in adherence was associated with a predicted 0.8% decrease in medical costs (95% CI -4.2-2.5%) but a predicted 6.1% increase in the risk of hospitalization for CHF (95% CI 0.5-12.0%). Among patients taking beta-blockers, a $10 increase in copayment was associated with a 1.8% decrease in the medication possession ratio (95% CI 1.4-2.2%). This change in adherence was associated with a predicted 2.8% decrease in medical costs (95% CI -5.9-0.1%) and a predicted 8.7% increase in the risk of hospitalization for CHF (95% CI 3.8-13.8%).
Conclusion: Among patients with CHF, higher drug copayments were associated with poorer adherence. The change was relatively small and did not affect predicted total health care costs, but it was sufficient to increase the predicted risk of hospitalization for CHF.