GABITRIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).
Tiagabine inhibits gamma-aminobutyric acid (GABA) reuptake into presynaptic neurons, thereby increasing synaptic GABA levels and enhancing inhibitory neurotransmission.
| Metabolism | Primarily hepatic via CYP3A4 and to a lesser extent CYP2C19; also undergoes glucuronidation. |
| Excretion | Approximately 70% of an oral dose is excreted in feces, 25% in urine, and 5% in bile. Renal elimination of unchanged drug is minimal (<2%); most is eliminated as metabolites. |
| Half-life | Terminal elimination half-life is 7–9 hours in healthy adults. In patients with hepatic impairment, half-life is prolonged (up to 12–24 hours) due to reduced clearance. No significant effect of renal impairment. |
| Protein binding | 96% bound to plasma proteins, primarily albumin and alpha1-acid glycoprotein. Binding is saturable and concentration-dependent. |
| Volume of Distribution | Volume of distribution is approximately 1.1 L/kg (range 0.9–1.4 L/kg). This indicates extensive tissue distribution, with drug levels in tissues exceeding plasma levels. |
| Bioavailability | Oral bioavailability is approximately 90% (range 80–100%) with minimal first-pass metabolism. Food reduces the rate but not extent of absorption. |
| Onset of Action | Oral: Peak concentrations occur at 1–2 hours; clinical effect (antiepileptic) typically begins within 1–2 weeks of regular dosing. Intravenous: not available (Gabitril is oral only). |
| Duration of Action | Duration of antiepileptic effect is approximately 6–12 hours, consistent with dosing every 6–8 hours. Sustained efficacy requires regular dosing due to relatively short half-life. |
| Molecular Weight | 412.46 |
Initial dose: 4 mg orally twice daily. Titrate by 4-8 mg/day every 2 weeks. Maximum dose: 56 mg/day in 2-4 divided doses.
| Dosage form | TABLET |
| Renal impairment | No adjustment required for mild to moderate renal impairment. For severe renal impairment (CrCl < 30 mL/min), reduce dose by 50%. |
| Liver impairment | Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50% or increase dosing interval. Child-Pugh C: Contraindicated or use extreme caution with significant dose reduction (e.g., 75% reduction) and slow titration. |
| Pediatric use | Not FDA-approved for pediatric use. Off-label use: For partial seizures, initial dose 0.1 mg/kg/day in 2 divided doses, titrate slowly up to 0.5-1 mg/kg/day. Maximum 56 mg/day. |
| Geriatric use | Start at lower end of dosing range (e.g., 2 mg twice daily). Monitor renal function; adjust based on creatinine clearance. Increased risk of dizziness and confusion. |
| 1st trimester | Teratogenic effects observed in animal studies; human data limited. Use only if benefit outweighs risk. |
| 2nd trimester | Potential for fetal harm; monitor fetal growth and development. Use only if clearly needed. |
| 3rd trimester | Risk of neonatal withdrawal or sedation; consider tapering prior to delivery. |
Clinical note
Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).
| Placental transfer | Crosses placenta in humans; fetal plasma concentrations may reach 30-50% of maternal levels. |
| Breastfeeding | Excreted into breast milk in low concentrations; monitor infant for drowsiness, poor feeding, or weight loss. Use with caution. |
| Lactation Rating |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to tiagabine or any component of the formulationSevere hepatic impairment
| Precautions | Risk of new-onset seizures or status epilepticus, especially with rapid dose escalation or abrupt discontinuation, Central nervous system depression (e.g., sedation, dizziness, ataxia), Suicidal ideation and behavior, Use with caution in hepatic impairment |
| Food/Dietary | Take with food to minimize gastrointestinal side effects. Avoid alcohol. Grapefruit juice has not been reported to interact, but caution is advised with other CNS depressants. |
| Clinical Pearls |
Loading safety data…
| L3 (Moderately Safe) |
| Teratogenic Risk | Pregnancy category C. First trimester: Risk cannot be ruled out; animal studies show developmental toxicity at clinically relevant doses, but human data limited. Second/third trimesters: Potential for increased seizure frequency due to pregnancy-induced pharmacokinetic changes, which may indirectly harm fetus. Use only if benefit outweighs risk. |
| Fetal Monitoring | Periodic monitoring of tiagabine plasma levels (if available) and seizure frequency. Assess for dose-dependent adverse effects. Fetal growth ultrasound if prolonged use. In neonates, observe for withdrawal symptoms (irritability, jitteriness) if used near term. |
| Fertility Effects | No human data on fertility effects. Animal studies showed no impairment of fertility at clinically relevant doses. Theoretical concerns with any antiepileptic drug on reproductive hormones. |
| Monitor for new or worsening depression, suicidal ideation, or unusual mood changes. Gabitril (tiagabine) is contraindicated in patients with severe hepatic impairment. Dose titration should be slow due to risk of CNS depression and dizziness. Abrupt discontinuation may precipitate withdrawal seizures. Tiagabine is not effective for absence seizures and may exacerbate them. |
| Patient Advice | Take with food to reduce stomach upset. · Do not drive or operate heavy machinery until you know how this medication affects you, as it may cause dizziness or drowsiness. · Avoid alcohol and other CNS depressants as they can increase sedation. · Notify your doctor immediately if you experience mood changes, depression, or suicidal thoughts. · Do not stop taking this medication abruptly as it may increase seizure frequency or cause withdrawal symptoms. · Take exactly as prescribed; do not change dose without consulting your doctor. |