Phenobarbital Dosing for Neonates
For neonates with seizures, the recommended loading dose of phenobarbital is 15-20 mg/kg intravenously, followed by a maintenance dose of 3-5 mg/kg/day. 1, 2, 3
Loading Dose
- Initial loading dose: 15-20 mg/kg IV
- Administer slowly, not exceeding 1 mg/kg/minute
- This loading dose typically achieves therapeutic plasma levels (15-30 μg/mL) within minutes 3
- For refractory seizures, additional boluses of 5-10 mg/kg may be given until seizures cease or serum concentration reaches 40 μg/mL 4
Maintenance Dosing
- Begin 12-24 hours after loading dose
- 3-5 mg/kg/day IV or divided into 1-2 daily doses 2, 3
- Do not exceed 5 mg/kg/day to avoid drug accumulation due to the long half-life in neonates (69-165 hours) 3
Monitoring
- Target therapeutic serum levels: 15-30 μg/mL 3, 5
- Monitor plasma levels regularly due to variable metabolism in neonates
- First level should be checked 24 hours after loading dose
- Subsequent monitoring every 3-5 days until stable
Duration of Therapy
- Generally, early discontinuation after 1-2 weeks is possible for most neonates 3
- Duration should be individualized based on seizure etiology and clinical response
Special Considerations
Preterm vs. Term Neonates
- Preterm neonates (<32 weeks) may show better response to phenobarbital 4
- However, no significant difference in plasma phenobarbital levels between term and preterm infants has been observed 6
Refractory Seizures
- If seizures persist despite phenobarbital levels of 40 μg/mL, consider adding a second anticonvulsant 4
- Do not use additional anticonvulsant drugs until phenobarbital plasma level exceeds 40 μg/mL 3
Administration Precautions
- Administer IV phenobarbital slowly to avoid respiratory depression
- Have resuscitation equipment readily available
- Monitor vital signs closely during administration
- Use larger veins for administration to minimize risk of irritation 2
Adverse Effects
- Respiratory depression (more common at higher doses)
- Hypotension
- Sedation
- Feeding difficulties (particularly at levels >50 μg/mL) 4
- Side effects are generally minimal when plasma levels remain in the therapeutic range 6
Phenobarbital remains the first-line drug for neonatal seizures due to its efficacy and relatively favorable safety profile when properly dosed and monitored.