Association of antiepileptic drug nonadherence with risk of seizures in adults with epilepsy

This study evaluated the potential effect of antiepileptic drug (AED) nonadherence on the risk of subsequent seizure. Retrospective insurance claims from the United States were analyzed. Inclusion criteria were: age 21–64 years, diagnosis of epilepsy or nonfebrile convulsions, ⩾2 AED prescriptions, and insurance enrollment for ⩾6 months pre- and ⩾60 days post-AED initiation. Seizure was defined as a hospital or emergency admission associated with epilepsy or nonfebrile convulsions. Observation began 7 days post-drug initiation, ending with the first of the following: seizure, insurance disenrollment, or 365 days post-drug initiation. Adherence was measured using the medication possession ratio (MPR), with MPR <0.8 defining nonadherence. Seizure risk was assessed using an extended Cox proportional hazards model. Of 18,073 subjects identified, 2467 (14%) had ⩾1 seizure. Mean follow-up was 133 days among subjects with event and 305 days for patients without event. Seizure risk was 21% higher among nonadherers (hazard ratio = 1.205, P = 0.0002) than adherers.