Carisbamate as adjunctive treatment of partial onset seizures in adults in two randomized, placebo-controlled trials

Purpose: To assess the efficacy, safety, and tolerability of the investigational drug carisbamate as adjunctive treatment for partial-onset seizures (POS). Methods: Two identical, randomized, placebo-controlled, double-blind studies were conducted in adults with POS uncontrolled for ≥1 year. Therapy-refractory epilepsy patients (≥16 years) remained on stable doses of prescribed antiepileptic drugs (≤2) for an 8-week prospective baseline phase and were then randomized (1:1:1) to carisbamate 200 mg/day, carisbamate 400 mg/day, or placebo, for a 12-week double-blind phase. Primary efficacy end points were percent reduction in seizure frequency and responder rate (patients with ≥50% reduction in POS frequency) during the double-blind phase compared with the prospective baseline phase. Results: Of the 565 patients randomized in study 1, 93% completed the study; of the 562 randomized in study 2, 94% completed the study. Patient characteristics were similar across both studies and treatment arms: mean age, 35 years (study 1, range 16-75 years) and 36 years (study 2, range 16-74 years); approximately 50% were men. Treatment with carisbamate 400 mg/day resulted in significant improvement (p < 0.01) in both efficacy measures compared with placebo in study 1 but not in study 2. Carisbamate 200 mg/day did not differ statistically from placebo in either study. Among the most common treatment-emergent adverse events (≥5% in any group), those with an incidence exceeding placebo (≥3%) were dizziness (400 mg/day group) and somnolence. Conclusions: Carisbamate 400 mg/day was effective in patients with refractory partial-onset seizures in one of these global studies. More than 200 mg/day of carisbamate is required for efficacy. Carisbamate was well-tolerated in both studies.