Association between copayment and adherence to statin treatment initiated after coronary heart disease hospitalization: a longitudinal, retrospective, cohort study

Abstract

Background: Despite substantial evidence supporting the effectiveness of statin treatment, when administered regularly for the secondary prevention of coronary heart disease (CHD), many patients are not adherent.

Objective: The objective of this study was to examine the relationship between copayment and adherence to statin treatment among patients who initiated statin treatment after discharge from a CHD hospitalization.

Methods: Databases containing inpatient admission, outpatient, enrollment, and pharmacy claims from 1999 to 2003 were utilized for this study. The sample consisted of adults who initiated statin treatment after hospitalization directly related to CHD. Adherence to statins was measured by medication possession ratio (MPR), a surrogate marker of adherence calculated as a percentage of days with statins on hand during a 1-year observation period. The relationship between copayment and adherence to statin treatment was examined using multivariate logistic regression models. Demographic and clinical characteristics were selected as control variables based on modified versions of the Andersen health services utilization model as well as previous study findings.

Results: A total of 5,548 patients met the study entry criteria and were included in the analysis. Of this number, 3,404 patients (61.4%) had an MPR of >or=80% and were considered adherent to statins. Compared with those who had a copayment <USD10, patients with a copayment >or=USD20 were significantly less likely to be adherent to statins (odds ratio, 0.42; 95% CI, 0.36-0.49). Other relevant factors significantly associated with low adherence were younger age (P < 0.001), female sex (P < 0.001), absence of dyslipidemia diagnosis (P < 0.001), presence of depression (P = 0.010), and concomitant use of nonstatin lipid-lowering drugs (P < 0.001).

Conclusions: Adherence during the 1-year period after statin initiation among CHD hospitalized patients was suboptimal, with more than one third of the patients not adherent to statin treatment. High prescription copayment appeared to be a significant barrier to statin adherence, even after adjusting for demographic and clinical variables.