What is the typical dosage of Phenobarbital (anticonvulsant) for treating epileptic seizures in children?

Phenobarbital Dosing for Epileptic Seizures in Children

For status epilepticus in children, administer phenobarbital 20 mg/kg IV over 10-15 minutes, with neonates receiving 10 mg/kg IV. 1

Status Epilepticus Dosing

Initial Loading Dose

• Children (non-neonates): 20 mg/kg IV administered over 10-15 minutes 1
• Neonates: 10 mg/kg IV 1
• Maximum initial dose: 1000 mg 1

The American Academy of Pediatrics guidelines specify 15-20 mg/kg over 10-15 minutes for status epilepticus, which achieves therapeutic blood levels of 10-15 mcg/mL 2. The FDA labeling confirms that loading doses of 15-20 mg/kg produce blood levels of approximately 20 mcg/mL shortly after administration in children and infants 2.

Additional Dosing for Refractory Seizures

• If seizures persist after the initial loading dose, administer additional doses of 5-10 mg/kg until seizures stop 2
• Some infants with refractory seizures may require serum concentrations up to 40-100 mcg/mL 3
• Do not administer additional anticonvulsants until phenobarbital plasma levels exceed 40 mcg/mL 4

Maintenance Therapy

Daily Maintenance Dosing

• Standard maintenance: 3-4 mg/kg/day 2, 4
• Anticonvulsant maintenance: 4-6 mg/kg/day for 7-10 days to achieve blood levels of 10-15 mcg/mL 2
• Maximum maintenance dose: Do not exceed 5 mg/kg/day to avoid drug accumulation due to the long half-life (69-165 hours in neonates) 4

The therapeutic serum concentration range is 10-25 mcg/mL for anticonvulsant use 2.

Critical Safety Considerations

Respiratory Monitoring

Phenobarbital carries significant risk of respiratory depression and hypotension, particularly when combined with other sedative agents. 1

• Be prepared to provide respiratory support with equipment for resuscitation and artificial ventilation available 2
• Monitor oxygen saturation continuously 1
• Vital signs must be recorded throughout administration 2

Administration Technique

• IV infusion rate: Administer over 10-20 minutes; do not exceed 1 mg/kg per minute 1
• Use larger veins; avoid small veins on the dorsum of the hand or wrist 2
• Never administer subcutaneously - causes tissue necrosis 2
• Avoid intraarterial injection - can cause gangrene requiring amputation 2

Special Populations

Neonates have increased risk of toxicity due to decreased protein binding; phenobarbital is specifically preferred over phenytoin in this age group. 1

The half-life in term neonates is 103 hours and in preterm infants is 141 hours, compared to 100 hours in adults 3. This prolonged half-life necessitates careful dosing to prevent accumulation 4.

Clinical Efficacy Context

The VA Cooperative Study demonstrated that phenobarbital is equally efficacious in managing status epilepticus when compared with lorazepam, phenytoin, and phenytoin plus diazepam 1. However, phenobarbital is typically used after benzodiazepines have failed in the treatment algorithm 1.

For focal epilepsy treated with oral high-dose phenobarbital (>5 mg/kg/day maintaining serum levels >40 mcg/mL), effectiveness was achieved in 7 of 15 children, with good tolerability 5.

Common Pitfall to Avoid

Do not continue injecting phenobarbital until convulsions stop - phenobarbital may require 15 minutes or more to attain peak brain concentrations after IV administration 2. If injected continuously until seizures cease, brain concentrations will continue rising and can cause excessive barbiturate-induced depression combined with postictal depression 2. Use the minimal amount required and wait for anticonvulsant effect to develop before administering additional doses 2.