SABRIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SABRIL (SABRIL).
Irreversible inhibitor of GABA transaminase, increasing brain gamma-aminobutyric acid (GABA) levels.
| Metabolism | Minimally metabolized; primarily excreted unchanged in urine. |
| Excretion | Primarily renal excretion as unchanged drug; approximately 70% recovered in urine within 24 hours, with an additional small amount as the inactive S(+)-enantiomer; minimal biliary/fecal elimination (<5%). |
| Half-life | Terminal elimination half-life is 5–8 hours in adults with normal renal function, but effective half-life for pharmacodynamic effect is longer (up to 24–48 hours) due to irreversible binding to GABA transaminase; half-life is prolonged in renal impairment (up to 15 hours in moderate impairment). |
| Protein binding | Less than 1% bound to plasma proteins; negligible binding. |
| Volume of Distribution | Approximately 0.8 L/kg, indicating distribution into total body water; clinically, low tissue binding and primarily extracellular distribution in line with hydrophilic properties. |
| Bioavailability | Oral bioavailability is approximately 60–80% (mean ~70%) due to saturable absorption at higher doses; food does not significantly affect absorption. |
| Onset of Action | Oral: time to maximum serum concentration (Tmax) is 1-2 hours; clinical anticonvulsant effect may be seen within a few days but optimal effect may require 1–2 weeks due to gradual enzyme inhibition. |
| Duration of Action | Duration of anticonvulsant effect persists for days after discontinuation due to irreversible inhibition of GABA transaminase; clinical effect can last up to 5–7 days after last dose despite shorter plasma half-life. |
| Molecular Weight | 129.16 |
For monotherapy of infantile spasms: 50 mg/kg/day orally divided twice daily, titrated over 7 days to 150 mg/kg/day. For refractory complex partial seizures: 500 mg twice daily, increased by 500 mg/week to a maximum of 3000 mg/day (1500 mg twice daily).
| Dosage form | TABLET |
| Renal impairment | GFR 50-80 mL/min: reduce dose by 25%; GFR 30-49 mL/min: reduce by 50%; GFR <30 mL/min: reduce by 75%. Hemodialysis: 500 mg after each dialysis. |
| Liver impairment | No specific adjustment for hepatic impairment; monitor for adverse effects as hepatic metabolism is minimal. |
| Pediatric use | Infantile spasms: Initial 50 mg/kg/day divided twice daily, titrate weekly by 50 mg/kg/day to 150 mg/kg/day. For partial seizures (off-label): 10-20 mg/kg/day divided twice daily, titrate to 40-60 mg/kg/day. |
| Geriatric use | Start at 500 mg twice daily; use lowest effective dose due to increased risk of visual field defects and renal clearance decline; monitor renal function and titrate slowly. |
| 1st trimester | Use only if benefit outweighs risk; associated with increased risk of major congenital malformations including neural tube defects (risk ~7%) |
| 2nd trimester | Use only if benefit outweighs risk; may cause fetal harm, consider alternative agents |
| 3rd trimester | Use only if benefit outweighs risk; neonatal withdrawal syndrome possible with third trimester exposure |
Clinical note
Comprehensive clinical and safety monograph for SABRIL (SABRIL).
| Placental transfer | Vigabatrin crosses the placenta; cord plasma concentrations approximately 50-80% of maternal plasma levels. |
| Breastfeeding | Vigabatrin is excreted into breast milk in low concentrations (milk-to-plasma ratio ~0.1-0.3). Monitor infant for potential adverse effects such as sedation, poor suckling, or developmental delays. Consider benefits of breastfeeding against potential risks. |
■ FDA Black Box Warning
May cause permanent bilateral concentric visual field constriction and other vision loss. Risk increases with cumulative dose and duration. Not indicated for treatment of other seizure types or conditions.
| Serious Effects |
Hypersensitivity to vigabatrin or any component of the formulationPre-existing visual field defects (unless benefit clearly outweighs risk)
| Precautions | Vision loss (permanent bilateral concentric visual field constriction, retinal abnormalities, optic nerve damage), Neurologic effects (somnolence, fatigue, dizziness, abnormal MRI signal changes, suicidal ideation), Hematologic effects (anemia, neutropenia), Peripheral edema, weight gain, Withdrawal seizures if abruptly discontinued |
| Food/Dietary | No clinically significant food interactions reported. Take with or without food. Alcohol should be avoided due to additive CNS depression and increased seizure risk. |
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| Lactation Rating | L3 (Moderately Safe) - Limited data suggest low risk; monitor infant. |
| Teratogenic Risk | Vigabatrin (SABRIL) is associated with an increased risk of fetal harm when administered during pregnancy. In animal studies, vigabatrin caused developmental toxicity including fetal structural abnormalities and reduced fetal weight. Human data are limited, but the drug crosses the placenta. Use during the first trimester carries a risk of major congenital malformations; use later in pregnancy may cause adverse neurological effects. Pregnancy category C. |
| Fetal Monitoring | Maternal: assess visual function (peripheral visual fields) at baseline and regularly (every 3 months). Monitor LFTs, CBC, and renal function. Fetal: if used during pregnancy, consider fetal ultrasound to assess growth and development. Newborns should be monitored for signs of neurotoxicity (e.g., sedation, hypotonia) if exposed near term. |
| Fertility Effects | In animal studies, vigabatrin caused decreased fertility and spermatogenic effects. Human data are lacking, but potential for reversible impairment of spermatogenesis exists. Effect on female fertility unknown. |
| Clinical Pearls | Vigabatrin (SABRIL) is associated with irreversible bilateral concentric visual field defects; mandatory ophthalmologic monitoring at baseline and every 3 months. It is indicated only for refractory complex partial seizures (CPS) in adults and infantile spasms in children 1 month to 2 years. Dose-dependent weight gain and peripheral edema are common. Avoid abrupt discontinuation to prevent withdrawal seizures. |
| Patient Advice | This drug can cause permanent vision loss; you must have eye exams before starting and every 3 months during treatment. · Do not stop taking this medicine suddenly; stopping abruptly can cause seizures that do not stop. · Report any vision changes, such as blurring, blind spots, or trouble seeing at night, immediately. · Avoid alcohol and other CNS depressants as they may increase drowsiness and dizziness. · Use effective contraception during treatment because this drug may harm an unborn baby. · You may experience weight gain, swelling in your legs or feet, or coordination problems; notify your doctor if these occur. |