VIGABATRIN

Clinical safety rating: safe

Animal studies have demonstrated safety

How it works

Irreversibly inhibits GABA transaminase, increasing brain GABA levels.

What the body does with it

Metabolism	Minimal hepatic metabolism; primarily excreted unchanged in urine (80% as parent drug). Not significantly metabolized by CYP450 enzymes.
Excretion	Renal: ~80% unchanged in urine; fecal: <5%.
Half-life	5-8 hours in young adults; 12-17 hours in elderly; prolonged with renal impairment.
Protein binding	Negligible (<5%).
Volume of Distribution	0.8-1.0 L/kg; suggests distribution into total body water.
Bioavailability	Oral: ~60-80% (fasting).
Onset of Action	Oral: 1-2 hours (peak plasma concentration); clinical effect in days to weeks for seizures.
Duration of Action	12-24 hours; may extend with accumulation due to irreversible MAO-B inhibition for Parkinson's; anticonvulsant effect persists beyond elimination due to GABA-T inhibition.

Classification & Brands

Dosing & administration

Adults: 500 mg orally twice daily; may increase by 500 mg/day every 7 days up to 1500 mg twice daily. For refractory complex partial seizures, maximum 3000 mg/day.

Dosage form	FOR SOLUTION
Renal impairment	CrCl >80 mL/min: 1000-3000 mg/day in 2 divided doses. CrCl 50-80 mL/min: 500-1500 mg/day in 2 divided doses. CrCl 30-50 mL/min: 250-1000 mg/day in 2 divided doses. CrCl 10-30 mL/min: 250-500 mg/day in 2 divided doses. CrCl <10 mL/min: 250 mg every 24-48 hours. Hemodialysis: 250 mg every 24-48 hours; supplement 125 mg after dialysis.
Liver impairment	No specific adjustment recommended; use with caution in severe hepatic impairment as safety not established.
Pediatric use	Infants 1 month to 2 years: 50 mg/kg/day divided twice daily, titrated weekly by 25-50 mg/kg/day to 100-200 mg/kg/day. Children 2-16 years: 40 mg/kg/day divided twice daily, titrated weekly by 25-50 mg/kg/day to 80-100 mg/kg/day (max 3000 mg/day).
Geriatric use	Initiate at lower doses (e.g., 250 mg twice daily) due to age-related renal function decline; titrate slowly monitoring for CNS effects. Adjust dose based on creatinine clearance.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other drugs that cause visual field defects may have additive effects Can cause permanent concentric visual field constriction.

Breastfeeding	Excreted into breast milk; M/P ratio approximately 0.1–0.8. Infant exposure is low, but potential for adverse effects such as sedation or hypotonia. Compatible with cautious use, but monitor infant for drowsiness and feeding difficulties.
Teratogenic Risk	First trimester: Increased risk of major congenital malformations, particularly neural tube defects and cardiac anomalies. Second and third trimesters: Risk of fetal toxicity including growth restriction and neurodevelopmental adverse effects.

Warnings & precautions

■ FDA Black Box Warning

Permanent bilateral concentric visual field constriction; visual acuity loss; retinal damage. Risk increases with cumulative dose and treatment duration. Visual monitoring required at baseline and every 3 months.

Side Effect Profile

Common Effects	infantile spasms
Serious Effects

Absolute Contraindications

["Hypersensitivity to vigabatrin or any component","Pre-existing visual field defects (absolute)","Severe renal impairment (CrCl <30 mL/min) without dose adjustment","Pregnancy (unless benefit outweighs risk)"]

Clinical Precautions

Precautions

["Visual field defects (dose- and duration-dependent)","Neurotoxicity (MRI abnormalities, intramyelinic edema)","Suicidal thoughts/behavior","Withdrawal: taper slowly to avoid rebound seizures","Renal impairment: dose adjustment required (CrCl <60 mL/min)","Use in pregnancy: teratogenicity (neural tube defects, fetal CNS abnormalities)"]

Clinical Tips & Counseling

Drug interactions

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