VIGABATRIN
Clinical safety rating: safe
Animal studies have demonstrated safety
Irreversibly inhibits GABA transaminase, increasing brain GABA levels.
| 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. |
| Molecular Weight | 129.16 |
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. |
| 1st trimester | Associated with increased risk of major congenital malformations, particularly neural tube defects and cleft palate. Use only if benefit outweighs risk. |
| 2nd trimester | Risk of fetal harm persists; may cause fetal vigabatrin exposure with potential for neurotoxicity. Use only if clearly needed. |
| 3rd trimester | May cause neonatal sedation and withdrawal symptoms. Use only if benefit justifies potential risk. |
Clinical note
Other drugs that cause visual field defects may have additive effects Can cause permanent concentric visual field constriction.
| Placental transfer | Crosses placenta readily; cord blood levels approximately equal to maternal plasma levels. |
| Breastfeeding | Excreted into breast milk in low concentrations; infant serum levels are low but case reports of infant drowsiness and poor feeding. Monitor infant for sedation and weight gain. |
■ 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.
| Common Effects | infantile spasms |
| Serious Effects |
Hypersensitivity to vigabatrin or any componentPregnancy (unless benefit outweighs risk, but considered absolute contraindication due to teratogenicity)
| 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) |
| Food/Dietary |
Loading safety data…
| Lactation Rating | L3 (Moderately Safe) |
| 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. |
| Fetal Monitoring | Monitor maternal hepatic function, visual fields (risk of peripheral visual field defects), and trough serum concentrations. Fetal monitoring includes serial ultrasound for growth and anatomy, and fetal echocardiography. Neonatal monitoring for hypotonia and respiratory depression. |
| Fertility Effects | Limited data; no established effect on fertility. In animal studies, no significant impairment observed. In humans, no reports of altered fertility. |
| No significant food interactions. Take with or without food. Maintain adequate hydration. Avoid alcohol due to increased sedation risk. |
| Clinical Pearls | Vigabatrin is a first-line treatment for infantile spasms (West syndrome) and a second-line agent for refractory complex partial seizures. It is an irreversible inhibitor of GABA transaminase, leading to increased brain GABA levels. Monitor for visual field defects, which can be asymptomatic and irreversible; baseline and periodic ophthalmologic exams are mandatory. Dose adjustment is needed for renal impairment. Abrupt discontinuation may precipitate rebound seizures. Avoid use in patients with pre-existing visual field defects or if benefit-risk is unfavorable. |
| Patient Advice | Take vigabatrin exactly as prescribed; do not stop suddenly without consulting your doctor. · This medication can cause permanent vision loss. You will need regular eye exams before and during treatment. · Report any vision changes, such as blurriness, tunnel vision, or difficulty seeing colors, immediately. · Avoid driving or operating heavy machinery until you know how vigabatrin affects you. · Inform your doctor about all other medications, especially those for epilepsy, as interactions may occur. · Do not drink alcohol while taking vigabatrin. · If you are pregnant, planning to become pregnant, or breastfeeding, discuss risks with your doctor. |