Adherence to Antiseizure vs Other Medications Among US Medicare Beneficiaries With and Without Epilepsy.

OBJECTIVE To 1) compare adherence to antiseizure medications (ASMs) versus non-ASMs among individuals with epilepsy, 2) assess the degree to which variation in adherence is due to differences between individuals versus between medication classes among individuals with epilepsy, and 3) compare adherence in individuals with versus without epilepsy. METHODS This was a retrospective cohort study using Medicare. We included beneficiaries with epilepsy (≥1 ASM, plus International Classification of Diseases, Ninth Revision, Clinical Modification diagnostic codes), and a 20% random sample without epilepsy. Adherence for each medication class was measured by the proportion of days covered (PDC) in 2013-2015. We used Spearman correlation coefficients, Cohen's kappa statistics, and multilevel logistic regressions. RESULTS There were 83,819 beneficiaries with epilepsy. Spearman correlation coefficients between ASM PDCs and each of the 5 non-ASM PDCs ranged 0.44-0.50, Cohen's kappa ranged 0.33-0.38, and within-person differences between each ASM's PDC minus each non-ASM's PDC were all statistically significant (p