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NERVOUS SYSTEM › ANTIEPILEPTICS › ANTIEPILEPTICS › Barbiturates and derivatives
phenobarbital
N03AA02
Forms & Strengths
- Tablet: 15 mg, 16.2 mg, 30 mg, 32.4 mg, 60 mg, 64.8 mg, 97.2 mg, 100 mg
- Elixir: 15 mg/5 mL, 20 mg/5 mL
- Injection: 65 mg/mL, 130 mg/mL
Adult Dosing
- Epilepsy (General/Focal): 60 mg to 200 mg orally once daily or in divided doses
- Status epilepticus: 10 mg/kg to 20 mg/kg IV infusion (max rate 50 mg/min)
- Sedation: 30 mg to 120 mg orally daily in 2-3 divided doses
- Preoperative sedation: 100 mg to 200 mg IM 60-90 minutes before surgery
Pediatric Dosing
- Neonatal seizures: Loading dose 15 mg/kg to 20 mg/kg IV; maintenance 3 mg/kg to 5 mg/kg/day IV or orally
- Epilepsy (Children): 3 mg/kg to 6 mg/kg orally once daily or in divided doses
- Status epilepticus (Pediatric): 15 mg/kg to 20 mg/kg IV single dose
Indications
- Management of generalized tonic-clonic and partial seizures
- Treatment of neonatal seizures
- Short-term treatment of insomnia and anxiety (historical/limited use)
- Preoperative sedation
Mechanism of Action
- Enhances GABA-A receptor activity by prolonging the duration of chloride channel opening
- Increases inhibitory neurotransmission in the central nervous system
- Suppresses the sensory cortex, decreases motor activity, and raises seizure threshold
Contraindications
- Hypersensitivity to barbiturates
- History of manifest or latent porphyria
- Severe respiratory depression or chronic obstructive pulmonary disease
- Severe hepatic impairment
Adverse Reactions
- Central nervous system depression (somnolence, sedation, ataxia, lethargy)
- Respiratory depression and apnea
- Hypotension and bradycardia (especially with rapid IV administration)
- Paradoxical excitement, hyperactivity in children, and confusion in the elderly
- Long-term use: osteomalacia, folate deficiency, megaloblastic anemia, and dependence/tolerance
Drug Interactions
- Potent CYP450 enzyme inducer (CYP3A4, 2C9, 2C19); decreases serum concentrations of oral anticoagulants, oral contraceptives, and corticosteroids
- Additive CNS depression with alcohol, opioids, benzodiazepines, and other sedatives
- Valproic acid inhibits phenobarbital metabolism, significantly increasing its serum concentrations
- May decrease the absorption and efficacy of certain medications like griseofulvin and doxepin
Curated Content: Needs Vetting Before Put to Clinical Use