Phenytoin Loading Dose Administration Protocol
The recommended phenytoin loading dose is 15-20 mg/kg administered intravenously at a maximum rate of 50 mg/minute in adults or 1-3 mg/kg/minute in pediatric patients (whichever is slower) to minimize cardiovascular adverse effects. 1
IV Loading Dose Administration
- Administer 15-20 mg/kg IV loading dose to achieve therapeutic serum concentrations (10-20 mcg/mL) 1
- Maximum infusion rate should not exceed 50 mg/minute in adults and 1-3 mg/kg/minute in pediatric patients 1, 2
- Dilute in normal saline (not dextrose solutions) to prevent precipitation 2
- With an 18 mg/kg dose, 97% of patients achieve therapeutic levels (>10 mcg/mL) immediately after infusion 3, 4
Monitoring During Administration
- Continuous cardiac monitoring is essential during infusion 1
- Monitor blood pressure every 15 minutes during infusion 4
- If cardiovascular complications occur (hypotension, bradycardia, arrhythmias), slow or temporarily stop the infusion 5
- For IV site irritation or burning (occurs in ~15% of patients), reduce infusion rate to 20 mg/minute 2, 4
Alternative Loading Strategies
- For less urgent situations, consider divided loading dose: 15 mg/kg divided into 3 IV injections given 2 hours apart 6
- In awake patients who can take oral medications, oral loading with 18 mg/kg can achieve therapeutic levels in 48-55% of patients within 3-10 hours 3
- For status epilepticus that doesn't respond to initial treatment, the Epilepsy Foundation of America recommends up to 30 mg/kg before using another antiepileptic drug 3
Maintenance Dosing
- Begin maintenance dosing based on 2-hour post-loading serum level 7
- If 2-hour level is >20 mcg/mL, delay maintenance dose until 12 hours post-loading 7
- If 2-hour level is 15-20 mcg/mL, begin maintenance dose at 6-8 hours post-loading 1, 7
- Standard maintenance dose is 100 mg IV or orally every 6-8 hours 1
Special Considerations
- Fosphenytoin can be administered faster (150 mg/minute) and is associated with fewer infusion site reactions 3
- In patients with renal or hepatic disease or hypoalbuminemia, monitor unbound phenytoin concentrations 1
- For status epilepticus, consider concomitant benzodiazepines for rapid seizure control while phenytoin is being administered 1
- Therapeutic effect typically occurs with serum total concentrations between 10-20 mcg/mL 1
Common Pitfalls to Avoid
- Never administer in dextrose-containing solutions (causes precipitation) 2
- Avoid intramuscular administration due to erratic absorption, pain, and tissue necrosis 1
- Do not exceed recommended infusion rates, as rapid administration increases risk of cardiovascular complications 1, 5
- Remember that phenytoin sodium injection is 92% phenytoin by weight - dosing calculations should account for this when switching between formulations 1