GABITRIL

Clinical safety rating: caution

Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).

How it works

Tiagabine inhibits gamma-aminobutyric acid (GABA) reuptake into presynaptic neurons, thereby increasing synaptic GABA levels and enhancing inhibitory neurotransmission.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).

Breastfeeding	Tiagabine is excreted in human milk at low concentrations; estimated relative infant dose is 0.1-0.3% of maternal weight-adjusted dose. M/P ratio not established. Monitor infant for drowsiness, poor feeding. Use caution.
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.

Warnings & precautions

■ FDA Black Box Warning

None.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to tiagabine or any component of the formulation","Severe hepatic impairment (Child-Pugh class C)"]

Clinical Precautions

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"]

Clinical Tips & Counseling

Drug interactions

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GABITRIL

Clinical safety rating: caution

Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).

How it works

Tiagabine inhibits gamma-aminobutyric acid (GABA) reuptake into presynaptic neurons, thereby increasing synaptic GABA levels and enhancing inhibitory neurotransmission.

What the body does with it

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.

Classification & Brands

Dosing & administration

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.

Use during pregnancy

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

Clinical note

Comprehensive clinical and safety monograph for GABITRIL (GABITRIL).

Breastfeeding	Tiagabine is excreted in human milk at low concentrations; estimated relative infant dose is 0.1-0.3% of maternal weight-adjusted dose. M/P ratio not established. Monitor infant for drowsiness, poor feeding. Use caution.
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.

Warnings & precautions

■ FDA Black Box Warning

None.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to tiagabine or any component of the formulation","Severe hepatic impairment (Child-Pugh class C)"]