Suboptimal statin adherence and discontinuation in primary and secondary prevention populations

Abstract

Objectives: To compare statin nonadherence and discontinuation rates of primary and secondary prevention populations and to identify factors that may affect those suboptimal medication-taking behaviors.

Design: Retrospective cohort utilizing pharmacy claims and administrative databases.

Setting: A midwestern U.S. university-affiliated hospital and managed care organization (MCO).

Patients: Non-Medicaid MCO enrollees, 18 years old and older, who filled 2 or more statin prescriptions from January 1998 to November 2001; 2258 secondary and 2544 primary prevention patients were identified.

Measurements: Nonadherence was assessed by the percent of days without medication (gap) over days of active statin use, a measurement known as cumulative multiple refill-interval gap (CMG). Discontinuation was identified by cessation of statin refills prior to the end of available pharmacy claims data.

Results: On average, the primary and secondary groups went without medication 20.4% and 21.5% of the time, respectively (P=.149). Primary prevention patients were more likely to discontinue statin therapy relative to the secondary prevention cohort (relative risk [RR], 1.24; 95% confidence interval [CI], 1.08 to 1.43). Several factors influenced nonadherence and discontinuation. Fifty percent of patients whose average monthly statin copayment was < US dollars 10 discontinued by the end of follow-up (3.9 years), whereas 50% of those who paid >US dollars 10 but <or=US dollars 20 and >US dollars 20 discontinued by 2.2 and 1.0 years, respectively (RR, 1.39 and 4.30 relative to <US dollars 10 copay, respectively).

Conclusions: Statin nonadherence and discontinuation was suboptimal and similar across prevention categories. Incremental efforts, including those that decrease out-of-pocket pharmaceutical expenditures, should focus on improving adherence in high-risk populations most likely to benefit from statin use.

FIGURE 1

Survival curves for discontinuation of statin therapy by prevention category. Adjusted for all available covariates. The median time to discontinuation was 3.7 years for secondary prevention and 3.4 years for primary prevention.

FIGURE 2

Survival curves for discontinuation of statin therapy by range of mean prescription copayment. Adjusted for all available covariates. The median time to discontinuation was 3.9+ years for $0 to <$10, 2.2 years for $10 to <$20, and 1.0 year for $20+.