This is a selective inhibitor of GABA transaminase.

Indications: treatment of refractory epilepsy, particularly partial epilepsy in adults and children, excluding petitmal, in addition to existing treatment; monotherapy for infantile spasms (West's Syndrome).

Cautions: renal impairment; elderly; closely monitor neurological function; avoid sudden withdrawal (taper off over 2–4 weeks); history of psychosis, depression or behavioural problems; pregnancy: and breast-feeding; absence seizures (may be exacerbated).

Contra-indications: visual field defects

Note: Onset of symptoms varies from 1 month to several years after starting. In most cases, visual field defects have persisted despite discontinuation. Product literature advises visual field testing before treatment and at 6- month intervals; a procedure for testing visual fields in those with a developmental age of less than 9 years is available from the manufacturers. Patients should be warned to report any new visual symptoms that develop and those with symptoms should be referred for an urgent ophthalmological opinion. Gradual withdrawal of vigabatrin should be considered.

Side Effects: drowsiness and fatigue; dizziness, nervousness, irritability, behavioural effects such as excitation and agitation especially in children; depression, abnormal thinking, headache, nystagmus, ataxia, tremor, paraesthesia, impaired concentration; less commonly confusion, aggression, psychosis, mania, memory disturbance, visual disturbance (e.g. diplopia); also weight gain, oedema, gastro-intestinal disturbances, alopecia, rash; less commonly, urticaria, occasional increase in seizure frequency (especially if myoclonic), decrease in liver enzymes, slight decrease in haemoglobin; photophobia and retinal disorders (e.g. peripheral retinal atrophy); optic neuritis, optic atrophy, hallucinations.

Dose: with current antiepileptic therapy, initially 1 g daily in single or 2 divided doses then increased according to response in steps of 500 mg at weekly intervals; usual range 2–3 g daily (max. 3 g daily); CHILD initially 40 mg/kg daily in single or 2 divided doses then adjusted according to body-weight 10–15 kg, 0.5–1 g daily; body-weight 15–30 kg, 1–1.5 g daily; body-weight 30–50 kg, 1.5–3 g daily; body-weight over 50 kg, 2–3 g daily.

Infantile spasms (West's syndrome), monotherapy, 50 mg/kg daily, adjusted according to response over 7 days; up to 150 mg/kg daily used with good tolerability.