Post hoc analysis of a phase 3 study for treatment of uncontrolled focal seizures: Adjunctive cenobamate dose and seizure reduction by baseline seizure frequency

This post hoc analysis (n = 240) of a subset of study sites (10 eligible US sites) from an open-label phase 3 study assessed whether baseline seizure frequency (<3 seizures/28 days vs ≥3 seizures/28 days) impacted mean cenobamate dose required to achieve 100% seizure reduction, duration of this response, and responder rates. Patients with uncontrolled focal seizures taking stable doses of 1-3 antiseizure medications were administered increasing doses of cenobamate (12.5, 25, 50, 100, 150, 200 mg/day) over 12 weeks at 2-week intervals. Further increases to 400 mg/day by 50-mg/day biweekly increments were allowed during the maintenance phase. Eligible patients were required to have consistent raw seizure data and good-quality data for ≥ 85% of the time spent in the study. Data were assessed until last visit and at data cut-off, on or after September 1, 2019. Among all 240 patients, 127 (52.9%) had < 3 seizures/28 days, and 113 (47.1%) had ≥ 3 seizures/28 days at baseline. Among patients continuing cenobamate at data cut-off (n = 177), 51% (90/177) and 49% (87/177) had < 3 and ≥ 3 seizures/28 days at baseline, respectively. Retention rate at data cut-off was 73.8% (177/240 patients), and these patients had a median time on study of 32.9 months (range: 22.1-43.0 months). 33.9% of patients continuing cenobamate (60/177) achieved 100% seizure reduction for ≥ 12 months at data cut-off, with 44.4% and 23.0% in patients with < 3 and ≥ 3 seizures/28 days at baseline, respectively. Regardless of baseline seizure frequency, responder rates at ≥ 50%, ≥ 75%, and ≥ 90% during the maintenance phase were similar (∼81%, ∼62%, and ∼43%, respectively). Mean±SD cenobamate dose for patients continuing cenobamate was 254.0 ± 82.1 mg/day, with means of 237.9 ± 78.1 mg/day and 270.7 ± 83.1 mg/day in patients with < 3 and ≥ 3 seizures/28 days at baseline, respectively. Among patients who had 100% seizure reduction for ≥ 12 months at data cut-off (n = 60), the mean cenobamate dose was 226.4 ± 75.4 mg/day and 255.1 ± 93.7 mg/day in patients with < 3 and ≥ 3 seizures/28 days at baseline, respectively. The current data suggest that cenobamate was effective regardless of baseline seizure frequency, with both groups having a high number of patients reaching 100% seizure reduction. A higher percentage of patients with less vs more frequent seizures at baseline reached zero seizures, suggesting these patients may reach 100% seizure reduction at lower cenobamate doses than those with more frequent seizures. Cenobamate dose varied slightly (∼30 mg/day) across patients who were stratified by baseline seizure frequency, but future analyses are necessary to determine whether patients with more frequent seizures require higher doses of cenobamate to achieve zero seizures.