Phenobarbital Dosing in Neonates
The recommended intravenous phenobarbital dosing for neonates is a loading dose of 15-20 mg/kg followed by a maintenance dose of 3-5 mg/kg/day. 1
Loading Dose Administration
- Initial loading dose: 15-20 mg/kg IV administered slowly
- Rate of administration: Should not exceed 60 mg/min for phenobarbital sodium
- Therapeutic plasma levels (15-30 μg/mL) are typically achieved within minutes of injection
Maintenance Dosing
- 3-4 mg/kg/day for most neonates 2
- For infants ≤35 weeks gestation: 3.5-4.5 mg/kg/day 3
- For infants >35 weeks gestation: 4.0-5.0 mg/kg/day 3
- Maximum recommended maintenance dose: 5 mg/kg/day to avoid drug accumulation due to long half-life (69-165 hours in neonates) 2
Dosing Considerations
- Asphyxiated term infants may have higher trough concentrations and may require doses at the lower end of the recommended range 3
- Actual body weight is the most reliable parameter for dosing calculations 4
- Therapeutic monitoring is essential due to significant individual variation in drug metabolism
- Plasma concentration should be monitored frequently during the first month of life as clearance can change substantially 3
Administration Precautions
- Slow IV injection is essential
- Carefully monitor vital signs during administration
- Equipment for resuscitation and artificial ventilation should be available
- Use larger veins rather than small veins on the dorsum of hand or wrist
- Avoid administration into varicose veins due to retarded circulation 1
Duration of Therapy
- Generally, early discontinuation after 1-2 weeks should be possible depending on the clinical condition 2
- Gradual withdrawal is recommended after sustained improvement
Important Considerations
- No other anticonvulsant should be used until phenobarbital plasma level exceeds 40 μg/mL 2
- If seizures persist despite phenobarbital levels of 40 μg/mL, consider adding a second anticonvulsant rather than further increasing phenobarbital dose 5
- Preterm infants (<32 weeks gestation) typically show better response to phenobarbital than term infants 5
This evidence-based dosing regimen balances efficacy in seizure control with safety considerations in this vulnerable population.