Fosphenytoin

Hydantoin anticonvulsant
Water-soluble phosphate ester prodrug of Phenytoin
1. Fosphenytoin is hydrolyzed to Phenytoin by phosphatases
Increases Neuronal Sodium efflux and stabilizes Neuronal membranes in the motor cortex
Suppresses the propagation of Seizure activity in the motor cortex

Dosed in Phenytoin equivalents (PE)
Transition to oral Phenytoin as soon as possible
Therapeutic serum level range: 10 to 20 mcg/ml
Status Epilepticus
1. Dose: 15 to 20 PE mg/kg IV or IM (at 3 mg/kg/min up to 100 to 150 mg/min) up to 1000 mg maximum
2. Avoid IM dosing if possible
Non-Emergent Loading Infusion
1. Dose: 10 to 15 PE mg/kg IV (at 2 mg/kg/min up to 100 to 150 mg/min) up to 1000 mg maximum
Maintenance
1. Follows loading dose by 12 hours (Status Epilepticus or non-emergent loading)
2. For initial dosing only (later dosing should be based on serum levels)
  1. Start: 2 to 4 PE mg/kg infused slowly (1-2 mg/kg/min up to 100 mg/min) every 12 hours
3. Subsequent dosing (based on serum levels)
  1. Dose 4 to 8 mg PE/kg/day divided every 12 hours based on serum levels
Preferred over Phenytoin for Status Epilepticus
1. Fosphenytoin can be infused with dextrose
2. Fosphenytoin has lower risk of Arrhythmia (due to no Ethylene Glycol in base)
3. Fosphenytoin may be given IM or delivered a faster IV rate (not tissue toxic)
  1. However onset of activity is similar to that with Phenytoin (as Fosphenytoin is converted to active Phenytoin form)

See Phenytoin
Severe Hypotension and Cardiac Dysrhythmias
1. Infuse slowly
2. Cardiac and hemodynamic monitoring during infusion