Direct evidence of nonadherence to antiepileptic medication in refractory focal epilepsy

The adherence to medication in drug-resistant focal epilepsy (RFE) remains largely unknown. The present work aimed to assess the frequency of recent adherence to antiepileptic drugs (AEDs) in patients with RFE. This prospective observational study screened all patients with RFE, admitted to the Nancy University Hospital between April 2006 and September 2008, for a 5-day hospitalization without AED tapering. The adherence to AEDs was assessed by measuring serum drug levels on day 1 (reflecting the recent "at home" adherence) and day 5 (reflecting the individual reference concentration when drug ingestion was supervised). A patient was considered nonadherent if at least one of their serum drug levels was different between days 1 and 5. The day-1 value was considered different from day 5 when it was at least 30% lower (underdosed) or 30% higher (overdosed). Nonadherent patients were classified as under-consumers in the case of one or more underdosed day-1 values, over-consumers in the case of one or more overdosed day-1 values, or undefined if they exhibited both underdosed and overdosed day-1 values. Forty-four of the 48 screened patients were included. Eighteen (40.9%) of 44 patients were nonadherent. Among them, 12 (66.7%) were over-consumers, 4 (22.2%) were under-consumers, and 2 (11.1%) were undefined nonadherents. The study indicates that recent adherence to antiepileptic medication in this group of patients with RFE is poor. Overconsumption is the most frequent form of nonadherence in this population and should be specifically assessed to prevent its possible consequences in terms of AEDs dose-dependent adverse events.