Purpose: This study assessed the extent of refill nonadherence with antiepileptic drugs (AEDs) and the potential association between AED nonadherence and health care costs in an adult-managed care population. Methods: Retrospective claims from the PharMetrics database were analyzed. Inclusion criteria were: age >/=21, epilepsy diagnosis between January 01, 2000 and March 12, 2005, >/=2 AED prescriptions, and continuous health plan enrollment for >/=6 months prior to and >/=12 months following AED initiation. Adherence was evaluated using the medication possession ratio (MPR). Patients with an MPR <0.8 were classified as nonadherent. Multivariate regression was used to assess the effect of AED nonadherence on annualized cost outcomes. Regression covariates included patient demographics, Charlson Comorbidity Index (CCI), and follow-up duration. Results: Among patients meeting all inclusion criteria (N = 10,892), 58% were female, mean age was 44 years, mean CCI was 0.94, and mean follow-up was 27 months. Mean MPR was 0.78 and 39% of patients were nonadherent. AED nonadherence was associated with an increased likelihood of hospitalization (odds ratio [OR]= 1.110, p = 0.013) and emergency room (ER) admission (OR = 1.479, p < 0.0001), as well as increased inpatient and ER costs of $1,799 and $260 (both p = 0.001), respectively, per patient per year. Outpatient and other ancillary costs were not significantly affected by nonadherence. A large net positive effect of nonadherence on total annual health care costs remained (+$1,466, p = 0.034) despite an offset from reduced prescription drug intake. Discussion: Adherence with AEDs among adult epilepsy patients is suboptimal and nonadherence appears to be associated with increased health care costs. Efforts to promote AED adherence may lead to cost savings for managed care systems
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