What is the intravenous (IV) phenytoin dose for seizure management?

From the Guidelines

The recommended IV phenytoin loading dose for seizures is 18-20 mg/kg administered at a maximum rate of 50 mg/minute in adults. For a typical adult, this translates to approximately 1000-1500 mg given over 20-30 minutes 1. After the loading dose, maintenance dosing is usually 4-6 mg/kg/day divided into 2-3 doses (typically 100 mg every 6-8 hours). Administration requires cardiac monitoring due to potential cardiovascular side effects including hypotension and cardiac arrhythmias. Phenytoin should be administered in normal saline rather than dextrose solutions as it precipitates in glucose-containing fluids. Purple glove syndrome is a rare but serious complication, so proper administration through a large vein with saline flush before and after is important. Blood levels should be monitored, with a therapeutic range of 10-20 mcg/mL. Phenytoin works by blocking voltage-sensitive sodium channels in neurons, limiting repetitive firing of action potentials and thereby preventing seizure propagation. Fosphenytoin, a water-soluble prodrug of phenytoin, may be preferred when available as it can be administered more rapidly (150 mg/minute) with fewer infusion-related complications 1.

Some key points to consider when administering IV phenytoin include:

• Monitoring for adverse effects such as hypotension, cardiac dysrhythmias, and soft tissue injury with extravasation 1
• Using a filter and infusion pump to administer the medication 1
• Avoiding administration in glucose-containing solutions due to precipitation 1
• Monitoring blood levels to ensure therapeutic ranges are achieved 1

It's also important to note that other medications, such as valproate and levetiracetam, may be considered as alternatives to phenytoin in certain situations, such as refractory convulsive status epilepticus 1. However, the choice of medication and administration route should be individualized based on patient-specific factors and clinical judgment.

From the FDA Drug Label

In adults, a loading dose of 10 to 15 mg/kg should be administered slowly intravenously, at a rate not exceeding 50 mg per minute In the pediatric population, a loading dose of 15 to 20 mg/kg of phenytoin sodium intravenously will usually produce serum concentrations of phenytoin within the generally accepted serum total concentrations between 10 and 20 mcg/mL The drug should be injected slowly intravenously at a rate not exceeding 1 to 3 mg/kg/min or 50 mg per minute, whichever is slower.

The recommended IV phenytoin dose for seizures is:

• Adults: 10 to 15 mg/kg loading dose, administered at a rate not exceeding 50 mg per minute
• Pediatrics: 15 to 20 mg/kg loading dose, administered at a rate not exceeding 1 to 3 mg/kg/min or 50 mg per minute, whichever is slower 2 2

From the Research

IV Phenytoin Dose for Seizures

• The recommended IV phenytoin dose for seizures is 18 mg/kg given by IV infusion in either 0.45% or 0.9% sodium chloride at a rate no greater than 50 mg/min, resulting in therapeutic serum levels for up to 24 hours in most patients 3.
• Maintenance therapy with phenytoin should start at 4 to 7 mg/kg/day and be adjusted to both clinical response and serum levels 3.
• In cases of status epilepticus, phenytoin is effective in preventing recurrence of seizures and in treating most other forms of status epilepticus 3.
• A systematic review and meta-analysis found that levetiracetam might be more effective than phenytoin for the treatment of established status epilepticus and is associated with a lower incidence of more serious adverse events 4.
• Another study compared the efficacy of phenytoin, valproate, and levetiracetam as second-line treatment of status epilepticus, and found that levetiracetam failed more often than valproate, while phenytoin was not statistically different from the other two compounds 5.

Comparison with Other Antiepileptic Drugs

• A systematic review comparing the efficacy of levetiracetam and phenytoin in reducing the incidence of late post-traumatic seizures found no significant difference, although levetiracetam showed an improvement in the Extended Glasgow Outcome Scale (GOS-E) 6.
• A survey of UK neurosurgical prescribing practice found that phenytoin was still the most commonly used antiepileptic medication for prophylaxis, but levetiracetam was gaining popularity due to its superior side-effect profile 6.