Antiepileptic — GABA Transaminase Inhibitor Pregnancy: Vigabatrin oral solution should not be used during pregnancy unless the clinical condition of the woman requires treatment with vigabatrin. Abnormal outcomes (congenital anomalies or spontaneous abortion) have been reported from spontaneous reports in the offspring of mothers taking vigabatrin, but no definite conclusion can be drawn because of limited data and concomitant antiepileptics; animal studies have shown reproductive toxicity. There is limited information on the possible occurrence of visual field defect in children exposed in utero. In offspring of women treated with antiepileptic medication generally, the prevalence of malformations is two to three times greater than in the general population, and monotherapy should be practised whenever possible. Vigabatrin is excreted into human milk with insufficient information on effects in newborns/infants — decide whether to discontinue breast-feeding or the medicine, taking account of the benefit of each (§4.6).

Vigabatrin

Brand names: Sabril

Vigabatrin is an antiseizure medicine used for refractory focal seizures and as a first-line treatment for infantile spasms (West syndrome).

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Adults: a starting dose of 1 g daily should be added to the patient's current antiepileptic medicinal product regimen, then titrated in 0.5 g increments at weekly intervals depending on clinical response and tolerability. Maximal efficacy is usually seen in the 2–3 g/day range

Route: Oral (oral solution 100 mg/mL) — may be taken before or after meals

Frequency: Once or twice daily

Max: 3 g/day — the highest recommended dose is 3 g/day

Treatment may only be initiated by a specialist in epileptology, neurology or paediatric neurology, with follow-up under specialist supervision. Except for the treatment of infantile spasms, vigabatrin should not be initiated as monotherapy. If the control of epilepsy is not clinically significantly improved after an adequate trial, treatment should not be continued; vigabatrin should be gradually withdrawn under close medical supervision. No direct correlation exists between plasma concentration and efficacy. Visual field defects have been reported with a high prevalence (about 1/3 of patients), usually after months to years of therapy, and available data suggest they are irreversible even after discontinuation — patients should undergo systematic screening examination when starting vigabatrin and visual field testing and assessment of visual acuity should continue at 6 month intervals for the whole duration of treatment; vigabatrin is not recommended in patients with any pre-existing clinically significant visual field defect. Paediatric population — resistant partial epilepsy: recommended starting dose in neonates, children and adolescents is 40 mg/kg/day, with maintenance in relation to bodyweight of 10 to 15 kg: 0.5–1 g/day; 15 to 30 kg: 1–1.5 g/day; 30 to 50 kg: 1.5–3 g/day; over 50 kg: 2–3 g/day — the maximum recommended dose in each of these categories should not be exceeded. Monotherapy for infantile spasms (West's syndrome): recommended starting dose 50 mg/kg/day, which may be titrated over a period of one week if necessary; doses of up to 150 mg/kg/day have been used with good tolerability.

Paediatric dose

Route: Oral (oral solution 100 mg/mL)

Frequency: Daily — vigabatrin oral solution is for oral administration once or twice daily

Max: Resistant partial epilepsy: the maximum recommended dose in each bodyweight category should not be exceeded (10 to 15 kg: 0.5–1 g/day; 15 to 30 kg: 1–1.5 g/day; 30 to 50 kg: 1.5–3 g/day; over 50 kg: 2–3 g/day). Infantile spasms: doses of up to 150 mg/kg/day have been used with good tolerability

Two distinct paediatric per-kg regimens are stated, so a single dosePerKg value is left null. Resistant partial epilepsy: 'The recommended starting dose in neonates, children and adolescents is 40 mg/kg/day', with weight-band maintenance doses as above. Monotherapy for infantile spasms (West's syndrome): 'The recommended starting dose is 50 mg/kg/day. This may be titrated over a period of one week if necessary. Doses of up to 150 mg/kg/day have been used with good tolerability.' Treatment may only be initiated by a specialist in epileptology, neurology or paediatric neurology. Visual field defects can only be reliably detected by systematic perimetry, which is usually possible only in patients with a developmental age of more than 9 years; a field-specific Visual Evoked Potential method is available from the company for children aged 3 years and above but has not been validated for detecting vigabatrin-attributed visual field defects, and electroretinography should be used only in adults unable to cooperate with perimetry or in the very young. Brain MRI abnormalities and intramyelinic oedema have been reported, particularly in infants.

Dose adjustments

Renal

Since vigabatrin is eliminated via the kidney, caution should be exercised when administering to older people and more particularly to patients with creatinine clearance less than 60 mL/min. Adjustment of dose or frequency of administration should be considered; such patients may respond to a lower maintenance dose and should be monitored for undesirable effects such as sedation or confusion (§4.2).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to vigabatrin or to any of the excipients

Side effects

Visual field defect (very common) — ranging from mild to severe, potentially disabling and generally irreversible; as many as 1/3 of patients develop them
Somnolence (very common); in adults mostly CNS effects such as sedation, drowsiness, fatigue and impaired concentration, whereas in children excitation or agitation is frequent
Fatigue (very common)
Agitation, aggression, nervousness, depression, paranoid reaction and insomnia (common)
Speech disorder, headache, dizziness, paraesthesia, disturbance in attention and memory impairment, mental impairment and tremor (common)
Weight increased, arthralgia, oedema and irritability (common); nausea, vomiting and abdominal pain (common)

Interactions

Phenytoin — vigabatrin may cause a moderate reduction in total phenytoin plasma levels; routine phenytoin dose adjustment is not required but should be considered if clinically indicated (US label §7.1)
Clonazepam — vigabatrin may moderately increase the Cmax of clonazepam, resulting in an increase of clonazepam-associated adverse reactions (US label §7.1)
Phenobarbital and sodium valproate — no clinically significant pharmacokinetic interactions; carbamazepine, clorazepate, primidone and sodium valproate appear to have no effect on plasma concentrations of vigabatrin (US label §7.1)
Steroid oral contraceptives — vigabatrin is unlikely to affect their efficacy (US label §7.2)
Drug-laboratory test interaction: vigabatrin decreases ALT and AST plasma activity in up to 90% of patients, which may preclude the use of these markers to detect early hepatic injury (US label §7.3)
Note: no §4.5 interactions section was present in the fetched eMC bundle — the items above are from US labelling and must be verified against the UK SPC

Clinical monograph

How it works

It is an irreversible inhibitor of GABA transaminase, the enzyme that degrades GABA, thereby raising brain GABA concentrations and enhancing inhibitory neurotransmission.

Prescribing in practice

It can cause permanent, irreversible concentric visual field constriction, so the benefits and risks must be discussed and vision assessed where feasible, with treatment limited to indications where the benefit justifies this risk.
Sedation, weight gain and behavioural changes can occur, and MRI signal changes have been reported in infants.
It should be withdrawn gradually to avoid precipitating seizures.

Monitoring

Arrange baseline and periodic visual field testing where the child or adult can cooperate, and monitor for behavioural change and excessive sedation.

Counselling the patient

Be aware of the risk of permanent loss of peripheral vision and attend any recommended eye tests.
Do not stop the medicine suddenly, as this can bring on seizures.

Evidence & guidelines

Its first-line role in infantile spasms and the visual field risk are reflected in NICE guidance and MHRA safety advice.

Reference: NICE NG217; MHRA Vigabatrin Visual Field Guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways