Dose Ranging Study of the Efficacy and Tolerability of Tonabersat in the Prophylaxis of Migraine Headache

A multi-centre, double-blind, placebo controlled, randomized, parallel group, dose ranging study to investigate the efficacy and tolerability of two different target doses of tonabersat and placebo in the prophylaxis of migraine. Following initial screening patients will enter a 4 week baseline assessment period, prior to randomization to one of three treatment groups. Subsequently patients will be allocated, according to the predetermined randomization schedule, to treatment with placebo or a target dose of tonabersat 40 mg/day or 80 mg/day in a 20 week treatment period. A dose titration regimen will be employed over a period of 4 weeks and treatment will then be maintained for a further 16 weeks. During the baseline assessment period and the treatment period patients will maintain a daily record (diary data) of the occurrence of migraine headache, the severity of an attack, the presence/absence of a preceding aura, other symptoms associated with the migraine and details of the use of rescue medication (patients will be permitted to use their usual symptomatic/acute treatment as rescue medication throughout the trial). Patients will attend the clinic for assessment and collection of blood and urine samples for laboratory analysis, and a sub-population of patients will participate in a pharmacokinetic study. A total of 7 visits are planned during the randomized double-blind treatment period. On completion of the randomized double-blind treatment period all patients will be offered the opportunity to enter an open label extension study where all patients receive tonabersat. A dose titration regimen will be employed over a period of 1 month and the final assigned dose of tonabersat (40, 60 or 80 mg/day) will be continued for the next 12 months. During the open label extension patients will attend the clinic for regular assessment of migraine status and safety. A total of 5 visits are planned.