Low-dose topiramate in adults with treatment-resistant partial-onset seizures

Objectives - Based on dose predictions from animal and human volunteer studies, most patients enrolled in initial randomized controlled trials of topiramate as adjunctive therapy in adults with partial-onset seizures were randomized to greater than or equal to 600 mg/day topiramate. Subsequent experience suggests that dosage needs were overestimated. This double-blind, placebo-controlled study evaluated 200 mg/day topiramate in adults with treatment-resistant partial-onset seizures receiving a concurrent enzyme-inducing antiepileptic agent (carbamazepine). Material and methods - After a 4-week baseline, 263 adults receiving carbamazepine who had at least three partial-onset seizures during the baseline period were randomized to placebo or one of two topiramate 200 mg/day treatment arms: topiramate escalated weekly 25 mg/day(8-week escalation) or 50 mg/day(4-week escalation). Therapy was then maintained for the remainder of the 12-week double-blind study. Results - Median percent reduction in seizure frequency from baseline to study end was 44% with topiramate and 20% with placebo (P less than or equal to 0.001). A significant therapeutic effect was present at 2 weeks with a dose of 100 mg/day. The most common adverse events (greater than or equal to10% incidence in topiramate-treated patients) were somnolence, fatigue, paresthesia, nervousness and anorexia; 8% of topiramate-treated patients and 2% of placebo-treated patients discontinued because of adverse events. As a result of the low incidence of adverse events, differences between titration rates in terms of tolerability were not detected. Conclusion - Topiramate 200 mg/day is an appropriate target dose as adjunctive therapy in adults with treatment-resistant partial-onset seizures, even when receiving an enzyme-inducing agent; 100 mg/day also appears to be effective. A significant therapeutic effect may be seen in the second week of treatment with a dose of 100 mg/day.