FOSPHENYTOIN

Clinical Use

Fosphenytoin sodium is a soluble pro-drug disodium phosphate ester of phenytoin (142 mg/mL) that was developed as a replacement for parenteral phenytoin sodium to circumvent the pH and solubility problems associated with parenteral phenytoin sodium formulations. Unlike phenytoin, fosphenytoin is freely soluble in aqueous solutions and is rapidly absorbed by the IM route. It is rapidly metabolized (conversion half-life, 8–15 minutes) to phenytoin by in vivo phosphatases. Therapeutic free (unbound) and total plasma phenytoin concentrations are consistently attained following IM or IV administration of fosphenytoin. It is administered IV following benzodiazepines for control of status epilepticus or whenever there is a need to rapidly achieve therapeutic plasma concentrations. Severe bradycardiac adverse events to fosphenytoin, including some fatalities, have been reported. A dose reduction in patients who are elderly or have renal or hepatic impairment has been suggested.