A risk-benefit assessment of vigabatrin in the treatment of neurological disorders.

Vigabatrin was designed to increase the levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the brain. It does this by replacing GABA as a substrate for the action of the catabolic enzyme GABA-transaminase. As a result of this inhibition, neuronal GABA levels are elevated, resulting in enhanced endogenous GABA transmission. A number of clinical trials assessing the effect of vigabatrin in epilepsy have been completed. Vigabatrin is of proven benefit in partial seizures and secondarily generalised tonic clonic seizures, and it is licensed for use as adjunctive therapy in these conditions in several European countries. It has been shown to be effective in some epilepsy syndromes in children including West's syndrome, infantile spasms and cryptogenic partial seizures. Its effect on primary generalised tonic clonic seizures is variable, while there is considerable evidence that it has a deleterious effect on myoclonic and absence seizures. There have been a few reports of the benefits of vigabatrin in other neurological disorders including tardive dyskinesia, degenerative ataxias and GABA metabolism disorders. The adverse effects associated with vigabatrin are similar to those seen with other anticonvulsants, with a predominance of CNS effects including somnolence, fatigue, irritability, dizziness and headache. Psychiatric symptoms including depression and psychosis are seen in a small number of patients and cause the most problems. These often necessitate discontinuation of vigabatrin, which usually results in resolution of symptoms.