What is the maximum dose of phenytoin (antiepileptic drug) in status epilepticus?

Maximum Dose of Phenytoin in Status Epilepticus

The maximum dose of phenytoin for status epilepticus is 20 mg/kg, with a maximum initial dose of 1000 mg, administered at a rate not exceeding 50 mg/minute in adults and 1-3 mg/kg/minute (or 50 mg/minute, whichever is slower) in pediatric patients. 1, 2

Dosing Guidelines

Initial Loading Dose:

• Adults: 10-15 mg/kg IV 2
• Children: 15-20 mg/kg IV 1, 2
• Maximum initial dose: 1000 mg 1

Administration Rate:

• Adults: Not exceeding 50 mg/minute 2
• Children: Not exceeding 1-3 mg/kg/minute or 50 mg/minute, whichever is slower 1, 2

Repeat Dosing:

• If seizures continue, an additional dose may be given after 15 minutes, with a maximum total dose of 40 mg/kg 1
• Maintenance doses of 100 mg IV every 6-8 hours should follow the loading dose 2

Administration Considerations

IV Administration Requirements:

• Administer directly into a large peripheral or central vein through a large-gauge catheter 2
• Dilute in normal saline (NOT dextrose solutions) 1, 2
• Test IV catheter patency with sterile saline flush before and after administration 2
• Continuous cardiac monitoring is essential during administration 2

Safety Precautions:

• Monitor heart rate continuously - reduce infusion rate if heart rate decreases by 10 beats per minute 1
• Monitor blood pressure continuously with an arterial line if possible 2
• Be prepared to provide respiratory support due to increased risk of apnea when combined with other sedative agents 1

Efficacy and Adverse Effects

Efficacy:

• In randomized controlled trials, phenytoin alone has shown a 44% success rate in terminating status epilepticus within 20 minutes 1
• When used after benzodiazepines, phenytoin has shown efficacy rates of 84% in some studies 1

Common Adverse Effects:

• Hypotension (occurs in approximately 12% of patients) 1
• Cardiac arrhythmias, especially with rapid infusion 1, 2
• Local irritation at injection site 2
• Respiratory depression 1

Alternative Considerations

If fosphenytoin is available, it is preferred over phenytoin due to:

• Lower risk of adverse cardiac effects 1
• Faster administration rates possible (150 mg PE/minute) 1
• Fewer local injection site reactions 1

Monitoring

• Therapeutic serum levels: 10-20 mcg/mL total phenytoin (1-2 mcg/mL unbound phenytoin) 2
• In patients with renal or hepatic disease or hypoalbuminemia, monitor unbound phenytoin concentrations 2
• Continuous EEG monitoring is recommended in refractory cases 3

Important Cautions

• Neonates have an increased risk of toxicity due to decreased protein binding; phenobarbital is preferred in this population 1
• Reduce dosage in patients with hepatic or renal impairment 2
• Never administer intramuscularly for status epilepticus due to erratic absorption and risk of tissue necrosis 2
• If 50% QRS widening or significant hypotension occurs during administration, hold the remainder of the dose 1