Phenobarbital Dosing for Seizure Management
For seizure management in adults, phenobarbital should be administered at 20 mg/kg IV over 10-15 minutes for status epilepticus, and 4-6 mg/kg/day for maintenance therapy to achieve serum levels of 10-15 mcg/mL. 1, 2
Adult Dosing
Status Epilepticus
- Initial loading dose: 20 mg/kg IV, administered over 10-15 minutes 2, 1
- For refractory seizures: Additional doses of 5-10 mg/kg may be given until seizures stop 3
- Maximum serum concentration may reach up to 40 μg/mL for therapeutic effect 3
- IV injection rate should not exceed 60 mg/min for phenobarbital sodium 1
Maintenance Therapy
- 4-6 mg/kg/day orally divided into 2-3 doses 1
- Target serum level: 10-15 mcg/mL 1
- For daytime sedation: 30-120 mg daily in 2-3 divided doses 1
Pediatric Dosing
Status Epilepticus
- 15-20 mg/kg IV over 10-15 minutes 2, 1
- Non-responders should receive additional doses of 5-10 mg/kg 3
Maintenance Therapy
- 4-6 mg/kg/day for 7-10 days to achieve blood level of 10-15 mcg/mL 1
- In neonates: 3-4 mg/kg/day orally for maintenance 3
Administration Considerations
Intravenous Administration
- Slow IV injection is essential to minimize adverse effects 1
- Use larger veins rather than small veins on the dorsum of the hand or wrist 1
- Monitor blood pressure, respiration, and cardiac function during administration 1
- Have resuscitation equipment available during administration 1
Intramuscular Administration
- Should be injected deeply into a large muscle 1
- Volume should not exceed 5 mL at any one site to prevent tissue irritation 1
- Avoid injection into or near peripheral nerves to prevent neurological deficit 1
Monitoring and Safety
- Monitor serum phenobarbital levels regularly to maintain therapeutic range 4
- Phenobarbital can cause hypotension in all patients requiring treatment with vasopressors 2
- Respiratory depression is a common adverse effect, especially with rapid administration 2
- Cognitive impairment may occur with long-term use, particularly in children 5
Special Considerations
- In refractory status epilepticus, higher doses may be needed - some studies have used mega-doses with serum levels up to 150 μg/mL 6
- Phenobarbital is a potent inducer of CYP3A4, leading to significant drug interactions 4
- Once-daily dosing may be effective for maintenance therapy in some patients with generalized epilepsy 7
- In patients with anoxic or metabolic disturbances, seizure control may be achieved in less than 40% of cases 2
Cautions and Contraindications
- Subcutaneous administration is not recommended 1
- Avoid inadvertent intraarterial injection which can lead to severe pain, spasm, and potential gangrene 1
- Phenobarbital may depress cognitive performance, with effects potentially outlasting drug administration 5
- Higher doses for refractory status epilepticus require careful risk-benefit analysis due to potential negative outcomes on survival and cardiorespiratory function 8