What is the proper administration protocol for phenytoin (antiepileptic medication)?

Phenytoin Administration Protocol

For safe and effective administration of phenytoin, use a loading dose of 10-15 mg/kg IV at a maximum rate of 50 mg/min in adults, followed by maintenance doses of 100 mg orally or IV every 6-8 hours. 1

IV Administration Guidelines

Loading Dose

• For adults with status epilepticus, administer 10-15 mg/kg IV at a rate not exceeding 50 mg/min (approximately 20 minutes for a 70-kg patient) 1
• For children, administer 15-20 mg/kg IV at a rate not exceeding 1-3 mg/kg/min or 50 mg/min, whichever is slower 1
• Therapeutic serum phenytoin levels (10-20 mcg/mL) are typically achieved within minutes after completion of the infusion 2

Administration Technique

• Administer directly into a large peripheral or central vein through a large-gauge catheter 1
• Test IV catheter patency with sterile saline flush before administration 1
• Follow each injection with a sterile saline flush to avoid local venous irritation due to the solution's alkalinity 1
• For infusion, dilute in normal saline with final concentration no less than 5 mg/mL 1
• Use an in-line filter (0.22-0.55 microns) for infusion administration 1
• Complete administration within 1-4 hours after preparation 1
• Never add phenytoin to dextrose-containing solutions due to precipitation risk 1, 3

Monitoring During Administration

• Continuous cardiac monitoring is essential during and after IV administration 1
• Monitor vital signs closely, especially blood pressure and heart rate via ECG 3
• Reduce infusion rate or discontinue if:
  • Heart rate decreases by 10 beats per minute 3
  • Hypotension develops 1
  • Cardiac arrhythmias occur 1
• Monitor for neurological side effects including ataxia, nystagmus, tremor, and somnolence 2

Alternative: Fosphenytoin Administration

• Fosphenytoin (a water-soluble prodrug of phenytoin) can be administered at 18 PE/kg IV at a maximum rate of 150 PE/min 3, 2
• Fosphenytoin has fewer adverse events compared to IV phenytoin loading 3, 2
• Therapeutic phenytoin levels are achieved within minutes after completion of the infusion 3
• Intramuscular administration of fosphenytoin produces therapeutic serum phenytoin levels within 1 hour 2

Oral Administration

• Oral loading of phenytoin can be administered as 20 mg/kg divided in maximum doses of 400 mg every 2 hours 2
• Therapeutic serum phenytoin levels are typically achieved between 3-8 hours after initial ingestion 2
• Maintenance oral dosing without loading can achieve therapeutic levels in 3-7 days 2

Therapeutic Monitoring

• Therapeutic effect occurs most often with serum total concentrations between 10-20 mcg/mL (unbound phenytoin 1-2 mcg/mL) 1
• Trough levels should be obtained just prior to the patient's next scheduled dose 1
• Peak levels indicate threshold for dose-related side effects 1
• For patients with renal or hepatic disease or hypoalbuminemia, monitor unbound phenytoin concentrations 1

Common Pitfalls and Cautions

• Rapid IV administration can cause cardiovascular collapse, CNS depression, and cardiac arrest 1
• IV phenytoin contains propylene glycol (40%) and ethanol (10%) with pH of 12, contributing to adverse effects 2
• Purple glove syndrome, tissue necrosis, and phlebitis are potential complications of IV phenytoin 2
• If refrigerated or frozen, undiluted phenytoin may form a precipitate (will dissolve at room temperature) 1
• A faint yellow coloration may develop but does not affect potency 1

By following these guidelines, phenytoin can be administered safely and effectively while minimizing the risk of adverse events that could compromise patient outcomes.