Increased seizure frequency associated with felbamate withdrawal in adults.

Abstract

To characterize changes in seizure frequency following felbamate withdrawal. Nonrandomized, retrospective chart review of a case series. Epilepsy program specializing in adults with uncontrolled epilepsy. Forty-five ambulatory patients withdrawn from felbamate use. Patients were included if they had received felbamate for at least 1 month, were 18 years or older, had accurate seizure frequency documentation, had accurate documentation of all antiepileptic drugs, and received the same concomitant antiepileptic drugs before and after felbamate therapy, except for the possible addition of gabapentin. Patients were excluded if they had hematologic or hepatic toxic effects with felbamate, were unable to withdraw from felbamate treatment, had a progressive neurologic disorder, or participated in another drug trial. When information became available on aplastic anemia and hepatotoxicity associated with felbamate, all patients were advised to taper their felbamate dosage over approximately 2 weeks. They received written instructions for tapering felbamate and adjusting concomitant antiepileptic drugs and kept calendars to note the number of seizures. The charts of all patients who received felbamate were evaluated for adherence to inclusion and exclusion criteria. Statistical analysis was performed using a log-linear model for count data. Seizure frequency during the 6 months before initiating felbamate therapy served as the baseline. Changes in seizure frequency were evaluated by comparing the number of seizures in the month felbamate was tapered and the 3 months after felbamate discontinuation with the baseline frequency. Comparisons were made between patients who started gabapentin therapy and those who did not and between felbamate responders and nonresponders. Felbamate withdrawal resulted in a significant (P=.02) increase in seizure frequency. Patients receiving gabapentin had a smaller increase in seizure frequency, but the difference was not statistically significant. There was no statistically significant difference in seizure frequency between felbamate responders and nonresponders. Felbamate withdrawal caused a significant increase in seizure frequency over the subsequent 3 months. These findings are important for clinical trial design and clinical practice.