Phenytoin Dosing for Seizures in Children
For acute seizure management in children, administer a loading dose of 15-20 mg/kg IV phenytoin at a rate not exceeding 1-3 mg/kg/min or 50 mg/min (whichever is slower), as this achieves therapeutic serum concentrations in the vast majority of pediatric patients. 1, 2
Loading Dose Protocol
The standard loading dose is 15-20 mg/kg IV for pediatric patients, which consistently produces therapeutic serum concentrations (10-20 mcg/mL) in most children 2. While a 10 mg/kg dose has been mentioned in some contexts, this lower dose is insufficient for acute seizure management and is primarily referenced for adult status epilepticus 2.
Evidence Supporting 15-20 mg/kg Dosing:
- The FDA-approved dosing for pediatric status epilepticus explicitly states 15-20 mg/kg as the loading dose 2
- Research confirms that 18 mg/kg achieves therapeutic concentrations (10-20 μg/mL) in 77% of children when measured 60-180 minutes post-infusion 3
- A more recent audit of the 20 mg/kg dose showed therapeutic levels in approximately 80% of patients, though supra-therapeutic levels occurred in 20% 4
Critical Administration Parameters
Infusion Rate (Non-Negotiable):
Never exceed 1-3 mg/kg/min or 50 mg/min, whichever is slower 1, 2. Rapid administration causes:
Dilution Requirements:
- Dilute only in normal saline to a final concentration ≥5 mg/mL 1, 2
- Never mix with dextrose solutions as precipitation occurs 1, 2
- Use an in-line filter (0.22-0.55 microns) for infusions 2
Mandatory Monitoring During Administration
Continuous cardiac and respiratory monitoring is required throughout the infusion 1:
- ECG monitoring for bradycardia, arrhythmias, and heart block 1
- Blood pressure monitoring for hypotension 1
- Reduce infusion rate if heart rate decreases by 10 beats/min 1
Clinical Effectiveness Timeline
- Seizure control typically occurs within 3 minutes of completing the loading dose in status epilepticus 5
- Therapeutic serum concentrations are maintained for >10 hours in approximately 63% of patients after a single loading dose 5
- Peak serum levels occur 60-180 minutes post-infusion 3, 4
Maintenance Dosing
Following the loading dose, initiate maintenance therapy at 100 mg every 6-8 hours (or age-appropriate dosing of 4-6 mg/kg/day divided) 2. Therapeutic drug monitoring should guide subsequent dose adjustments, with target trough levels of 10-20 mcg/mL 2.
Common Pitfalls to Avoid
- Using estimated weights can result in 78-138% of intended dose 4, leading to either subtherapeutic or toxic levels—always use actual weight when possible
- Intramuscular administration is contraindicated in status epilepticus as peak levels may not occur for up to 24 hours 2
- Do not refrigerate diluted phenytoin solutions as precipitation may occur 2
- Flush IV line with sterile saline after administration to prevent local venous irritation 2