Section 01 · Monograph
Vigabatrin
Reviewed Nov 2026FDA label
SabrilGABA-transaminase inhibitor
- Forms
- Tab: 500mg | Powder packet: 500mg
- Dose
- 1-3g/day divided BID
- MOA
- Irreversibly inhibits GABA-T
Black Box Warning
- Permanent bilateral concentric visual field constriction, including tunnel vision, occurs in a high proportion of patients; onset is unpredictable and can occur at any time, even after treatment is discontinued, and may worsen despite stopping the drug
- Risk increases with total cumulative exposure (dose and duration); there is no known dose or duration free of risk
- Because of this risk, vigabatrin is reserved for patients who have responded inadequately to other therapies and is available only through the restricted Vigabatrin REMS Program
Indications
- Adjunctive therapy for refractory complex partial seizures in patients age 2 years and older who have responded inadequately to several alternative treatmentsFDA-labeled
- Monotherapy for infantile spasms in patients 1 month to 2 years of age, where potential benefits are judged to outweigh the risk of vision lossFDA-labeled
Mechanism of Action
- Irreversible inhibitor of GABA-transaminase (GABA-T), the enzyme responsible for GABA degradation, leading to increased CNS levels of the inhibitory neurotransmitter GABA
- Because enzyme inhibition is irreversible, pharmacologic effects persist until new enzyme is synthesized
Full Dosing
Adult / usual
- Infantile spasms: initiate 50mg/kg/day in 2 divided doses; may titrate by increments every 3 days to a maximum of 150mg/kg/day
- Complex partial seizures, adults: initiate 1000mg/day in 2 divided doses; titrate in 500mg weekly increments to a usual maintenance of 3000mg/day (range 1000-3000mg/day); doses above 3000mg/day have not shown added benefit
Renal
- Reduce dose in renal impairment (drug is renally eliminated largely unchanged)
Pediatric
- Complex partial seizures, pediatric 2-16 years: weight-based divided dosing per label; patients >60kg dosed as adults
Contraindications
- No absolute contraindications specified; avoid in patients with significant pre-existing visual field loss unless benefit clearly outweighs further risk
Drug Interactions
- May decrease phenytoin plasma concentrations (mechanism unclear) — monitor phenytoin levels
- No clinically significant interaction demonstrated with oral contraceptives
- Additive CNS/sedative effects with other CNS depressants
Adverse Effects
- Permanent vision loss/visual field constriction (see boxed warning)
- Common: somnolence, fatigue, dizziness, weight gain, tremor, blurred vision, memory impairment
- MRI signal abnormalities (intramyelinic edema) reported, particularly in infants receiving high doses
- Peripheral neuropathy, more common with long-term use in adults
- Anemia, edema, suicidal ideation (class effect)
Monitoring Parameters
- Vision assessment (perimetry when age-appropriate, or alternative testing such as electroretinography in young children) at baseline, then approximately every 3 months during treatment, and 3-6 months after discontinuation
- Only prescribers, pharmacies, and patients enrolled in the Vigabatrin REMS Program may prescribe, dispense, or receive the drug
- Consider periodic MRI surveillance in infants for intramyelinic edema per specialist judgment
- Assess for emerging suicidal ideation
Pregnancy & Lactation
- Animal data show developmental toxicity/neurotoxicity at clinically relevant exposures; human data limited. Use only if potential benefit justifies fetal risk. NAAED Pregnancy Registry enrollment encouraged (1-888-233-2334)
- Vigabatrin is excreted into breast milk; effects on the nursing infant are unknown