Phenobarbitone Dosing for a 1-Year-Old Child Weighing 7.6 kg
For a 1-year-old child weighing 7.6 kg, the recommended phenobarbitone syrup dose is 6 mg/kg/day divided into 3 doses, which equals approximately 15 mg three times daily (45-50 mg total daily dose) for sedative purposes, or 15-50 mg two to three times daily for anticonvulsant therapy. 1
Weight-Based Calculation for Sedative Use
- The FDA-approved dosing for pediatric sedation is 6 mg/kg/day divided into 3 doses 1
- For this 7.6 kg child: 7.6 kg × 6 mg/kg = 45.6 mg total daily dose
- Practical divided dosing: 15 mg three times daily (morning, afternoon, evening) 1
Anticonvulsant Dosing (If Indicated)
- For seizure control, the FDA label specifies 15-50 mg given 2-3 times daily for children 1
- The loading dose in neonates is 20 mg/kg IV, with maintenance of 3-4 mg/kg orally, though this specific infant falls between neonatal and older pediatric dosing 2
- For this 7.6 kg child as anticonvulsant: start with 15-20 mg twice daily and titrate based on seizure control and serum levels 1, 2
Syrup Formulation and Administration
- Phenobarbitone syrup typically comes as 15 mg/5 mL or 20 mg/5 mL formulations
- For sedative dosing (15 mg per dose): give 5 mL of 15 mg/5 mL syrup three times daily 1
- Administer doses at consistent intervals (approximately every 8 hours for three-times-daily dosing) 1
Critical Safety Parameters
- Therapeutic serum concentration for anticonvulsant effect is up to 40 µg/mL, though refractory cases may require up to 100 µg/mL 2
- The half-life in infants around 1 year of age is approximately 67-100 hours, significantly longer than adults, requiring careful dose titration 2
- Monitor for drowsiness, lethargy, poor feeding, and irritability as common adverse effects 3
- Watch for respiratory depression, particularly if combined with other sedatives 4
Important Clinical Pitfalls
- Never exceed the weight-based calculation without serum level monitoring, as phenobarbitone has a very long half-life in infants and accumulates with repeated dosing 2
- The sedative dose (6 mg/kg/day) is substantially lower than anticonvulsant dosing requirements; do not confuse these indications 1, 2
- Phenobarbitone undergoes hepatic metabolism via CYP2C9, with 25% excreted unchanged in urine—adjust dosing in hepatic or renal impairment 2
- The drug takes 4-5 days to reach steady state in infants due to the prolonged half-life, so clinical effects and side effects may not be immediately apparent 2
Practical Prescribing Example
- Prescription: Phenobarbitone syrup 15 mg/5 mL
- Dose: Give 5 mL (15 mg) by mouth three times daily
- Total daily dose: 45 mg/day (approximately 6 mg/kg/day for this 7.6 kg child)
- Instructions: Administer at consistent 8-hour intervals; measure dose carefully with provided oral syringe 1