Vigabatrin: rational treatment for chronic epilepsy. Vigabatrin is a selective, irreversible suicide inhibitor of GABA transaminase and thus increases brain and CSF GABA. In 33 adult patients with long standing refractory epilepsy on treatment with one or two standard anti-convulsant drugs, the addition of vigabatrin up to 3g daily for eight weeks was associated with a 48.2% reduction in seizure frequency. Twenty patients who had exhibited a 50% or more reduction in frequency of one or more seizure types entered an eight week double-blind placebo controlled phase. Patients on vigabatrin maintained a 54.7% reduction of seizure frequency, whereas those on placebo showed an 18.6% increase in seizure frequency, a highly significant difference between the two groups. In the open phase, seven patients were withdrawn due to unacceptable and reversible adverse events. The commonest side effects were drowsiness, depression and mood instability, and headaches. Vigabatrin is a potentially valuable new treatment for chronic epilepsy, especially partial seizures with or without secondary generalisation. 