Phenobarbital

Phenobarbital is a long-acting barbiturate that binds to an allosteric site on the GABA-A receptor, increasing the duration (not frequency) of chloride channel opening — the opposite modulation pattern to benzodiazepines. At higher concentrations, it also directly activates GABA-A chloride channels independently of GABA (GABA-mimetic action) and depresses glutamate-mediated excitatory neurotransmission. Its anticonvulsant action occurs at sub-anesthetic doses, and its very long half-life (72-144 hours) enables once-daily dosing but also means steady state takes 2-3 weeks to achieve.

Adult

Oral (Epilepsy): 60–180 mg once daily, dose to be taken at night. Intravenous Injection (Status epilepticus): 10 mg/kg (max. per dose 1 g) at a rate not more than 100 mg/minute, injection to be diluted 1 in 10 with water for injections.

Pediatric

Oral (Epilepsy, Child 1 month–11 years): Initially 1–1.5 mg/kg twice daily, then increased in steps of 2 mg/kg daily as required; maintenance 2.5–4 mg/kg 1–2 times a day. Oral (Epilepsy, Child 12–17 years): 60–180 mg once daily. Slow Intravenous Injection (Status epilepticus, Neonate): Initially 20 mg/kg at a rate no faster than 1 mg/kg/minute, then 2.5–5 mg/kg 1–2 times a day.…

• Acute porphyrias
• children
• debilitated
• elderly
• history of alcohol abuse
• history of drug abuse
• respiratory depression (avoid if severe)
• Acute intermittent porphyria or porphyria variegata