What is the recommended starting dose of Dilantin (phenytoin) for initial treatment of seizures?

Starting Dose of Dilantin (Phenytoin)

For status epilepticus or acute seizure management, administer phenytoin 20 mg/kg IV at a maximum infusion rate of 50 mg/min (or 1 mg/kg/min in children), with a maximum initial dose of 1000 mg. 1

Intravenous Loading Dose

The standard IV loading dose is 15-20 mg/kg for adults and 20 mg/kg for children, infused over 10-20 minutes. 1

• In status epilepticus specifically, use 20 mg/kg as the loading dose to achieve rapid therapeutic levels and seizure control. 1
• The infusion rate must not exceed 50 mg/min in adults (or 1 mg/kg/min in children) to minimize cardiac complications including hypotension, bradycardia, and arrhythmias. 1, 2
• Neonates should receive 10 mg/kg due to increased risk of toxicity from decreased protein binding; phenobarbital is preferred in this population. 1
• This loading dose achieves therapeutic serum levels (10-20 mcg/mL) within 2 hours in most patients and maintains levels for up to 24 hours. 1, 2

Oral Loading Dose

For oral loading in non-emergent situations, administer 18-20 mg/kg divided into doses of maximum 400 mg every 2 hours. 1

• One effective oral regimen is 1000 mg divided as 400 mg, 300 mg, and 300 mg given at 2-hour intervals. 1
• Oral loading takes 5+ hours to reach therapeutic levels, making it unsuitable for acute seizure control. 1
• Approximately 48-55% of patients achieve therapeutic levels within 3-10 hours after oral loading. 1

Critical Safety Considerations

Cardiac monitoring is mandatory during IV phenytoin administration due to significant risk of hypotension (46% of patients), bradycardia, and arrhythmias. 1

• Reduce infusion rate by 50% if heart rate decreases by 10 beats per minute. 1
• Phenytoin must be diluted in normal saline only—it precipitates in glucose-containing solutions. 1
• Use an infusion pump and filter for IV administration. 1
• Fosphenytoin (15-20 PE/kg at maximum rate of 150 PE/min) is preferred when available due to lower risk of cardiac adverse effects and extravasation injuries. 1

Maintenance Dosing After Loading

Begin maintenance therapy at 4-7 mg/kg/day (typically 300 mg/day in adults) starting 6-12 hours after the loading dose. 1, 2

• For perioperative prophylaxis, maintenance is 250 mg IV every 8 hours. 3
• Steady-state therapeutic levels are achieved in 7-10 days (5-7 half-lives) with maintenance dosing alone. 4

Common Pitfalls to Avoid

• Never use a 15 mg/kg loading dose in perioperative settings—studies show 7 out of 10 patients fall below therapeutic range within 6 hours; use 15 mg/kg minimum. 3
• Do not load phenytoin orally in patients requiring immediate seizure control—IV route is essential for status epilepticus. 1
• Avoid phenytoin in neonates whose mothers used long-term opioids due to risk of acute withdrawal and seizures. 1
• Be prepared for respiratory support when combining with benzodiazepines, as apnea risk increases significantly. 1

Efficacy Data

• IV phenytoin at 15-18 mg/kg controls seizures in 80% of patients with repetitive seizures, though efficacy drops below 40% when anoxic or metabolic disturbances are present. 1
• A loading dose of 18 mg/kg achieves therapeutic levels (>10 mg/L) at 24 hours post-infusion in nearly all patients. 1