II. Indications: Adjunctive Therapy
- Simple Partial Seizure
- Complex Partial Seizure
- Bipolar Disorder (not FDA approved)
- Anxiety (not FDA approved)
- Neuropathic Pain (not FDA approved)
III. Mechanism
IV. Precautions
- Adjust dose in hepatic disease
V. Dosing
-
General
- Typically combined with enzyme-inducing anticonvulsants (e.g. Carbamazepine, Phenobarbital, Phenytoin, Primidone)
- Decrease starting dose and titration speed when NOT used with an enzyme-inducing anticonvulsant
- Adult
- Initial: 4 mg orally daily for first week
- Increase by 4 to 8 mg/day increments per day weekly (over 6 to 20 weeks)
- Divide dose 2 to 4 times daily after first week
- Maximum: 56 mg/day divided 2 to 4 times daily
- Child (age 12 to 18 years)
- Initial: 4 mg orally daily for first week
- Increase by 4 mg/day increments per day for first week, then up to 4 to 8 mg/day weekly thereafter (over 6 to 20 weeks)
- Divide dose 2 to 4 times daily after first week
- Maximum: 32 mg/day divided 2 to 4 times daily
VI. Adverse Effects: General
- Common (Dose related)
- Sedation
- Dizziness
- Lethargy
- Tremor
- Nervousness
- Irritability
- Abdominal Pain
- Cognitive Impairment
- Serious
- Neurotoxic in Overdose
- Status Epilepticus, New Seizueres, Nonconvulsive Status Epilepticus
VII. Adverse Effects: Overdose
- Timing
- Symptom onset 2 hours at 2 hours after ingestion
- Duration up to 24 hours after ingestion
- Symptoms
- Vomiting
- Cardiopulmonary
- Tachycardia
- Hypertension or Hypotension
- Respiratory depression
- Neurologic
- Somnolence (doses >8 mg in a 6 year old)
- Nonconvulsive Status Epilepticus (doses >96 mg in an adult)
- Confusion
- Agitation
- Tremor
- Dystonia
- Myoclonus
- Management
- See Unknown Ingestion
- Activated Charcoal in early presentations (<1-2 hours after ingestion) and controlled airway
- Seizures
- Benzodiazepines (preferred first-line)
- Barbiturates
- Status Epilepticus may require Endotracheal Intubation and Propofol
- Disposition
- Medically cleared if asymptomatic after 6 hours from time of ingestion
- References
- Tomaszewski (2024) Crit Dec Emerg Med 38(9):38
VIII. Safety
- Pregnancy Category C
- Unknown Safety in Lactation
IX. Pharmacokinetics
- High oral Bioavailability with peak effect at 1 hour after ingestion
- Elimination Half-Life 4.5 to 6 hours
X. Resources
XI. References
- (2022) Presc Lett, Resource #361206, Antiseizure Medications
- Olson (2020) Clinical Pharmacology, Medmaster Miami, p. 56-7
- Hamilton (2020) Tarascon Pocket Pharmacopoeia
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