Phenytoin Pediatric Dose — Anticonvulsant
Phenytoin is a hydantoin-class antiepileptic agent that stabilizes neuronal membranes by blocking voltage-gated sodium channels, thereby reducing repetitive neuronal firing. It is indicated in pediatric patients for the treatment and prevention of tonic-clonic and focal seizures, as well as status epilepticus refractory to first-line benzodiazepines. Phenytoin remains a cornerstone agent in both acute and chronic pediatric seizure management.
Pediatric Dosing
- Loading dose: 20 mg/kg IV (single dose)
- Maintenance dose: 5–10 mg/kg/day IV or PO, divided every 12 hours
The loading dose is administered as a single intravenous dose to rapidly achieve therapeutic serum concentrations. Maintenance therapy is initiated thereafter, divided into twice-daily dosing by either the intravenous or oral route, with dose individualized based on clinical response and serum drug levels.
Worked example — 20 kg child: Loading dose: 20 kg × 20 mg/kg = 400 mg IV (single dose). Maintenance: 20 kg × 5–10 mg/kg/day = 100–200 mg/day, given as 50–100 mg every 12 hours IV or PO. Consult institutional protocol for specific concentration, infusion rate limits, and maximum single dose guidance.
Indications and Clinical Context
Phenytoin is used in pediatric patients for acute seizure management, particularly in status epilepticus that has not responded to benzodiazepines, consistent with PALS and standard pediatric neurology guidelines. It is also employed for ongoing seizure prophylaxis in conditions such as post-traumatic seizures and neonatal seizures, where it serves as a second-line or adjunctive agent.
Therapeutic drug monitoring is essential to optimize efficacy and minimize toxicity. Target total phenytoin serum concentrations are typically 10–20 mcg/mL, though free (unbound) levels should be interpreted in patients with altered protein binding (e.g., neonates, hypoalbuminemia). Dose adjustments should be guided by clinical response and drug levels in consultation with neurology or pharmacy where available.
Administration and Monitoring
The loading dose must be administered intravenously at a controlled rate; rapid infusion is associated with cardiovascular adverse effects including hypotension, bradycardia, and cardiac arrhythmias. Phenytoin should be infused in normal saline (it is incompatible with dextrose-containing solutions) and administered through a dedicated IV line due to its alkaline pH and risk of precipitation. Continuous cardiac monitoring and blood pressure assessment are required during IV loading.
- Monitor for cardiac arrhythmias, hypotension, and local infusion-site reactions (purple glove syndrome)
- Assess for dose-dependent neurological side effects: nystagmus, ataxia, and sedation
- Oral bioavailability varies by formulation; ensure consistent use of brand or generic when transitioning routes
- Use with caution in patients with known cardiac conduction abnormalities or hepatic impairment
- Consult institutional protocol for maximum infusion rate and concentration limits
Disclaimer: This article is an educational reference summarizing standard pediatric dosing values. It is not a substitute for clinical judgment. Always verify doses against institutional protocols, the current edition of authoritative references (e.g., Lexicomp, Harriet Lane Handbook, PALS guidelines), the patient’s accurate weight, and any patient-specific factors (renal/hepatic function, allergies, comedications) before administration.