Fosphenytoin Sodium

Fosphenytoin sodium injection, USP is indicated for the control of generalized tonic-clonic status epilepticus and prevention and treatment of seizures occurring during neurosurgery. Fosphenytoin can also be substituted, short-term, for oral phenytoin. Fosphenytoin should be used only when oral phenytoin administration is not possible. Fosphenytoin must not be given orally.

Fosphenytoin sodium injection, USP is contraindicated in patients who have demonstrated hypersensitivity to fosphenytoin sodium injection, USP or its ingredients, or to phenytoin or other hydantoins. Because of the effect of parenteral phenytoin on ventricular automaticity, fosphenytoin injection is contraindicated in patients with sinus bradycardia, sino-atrial block, second and third degree A-V block, and Adams-Stokes syndrome.

Coadministration of fosphenytoin is contraindicated with delavirdine due to potential for loss of virologic response and possible resistance to delavirdine or to the class of non-nucleoside reverse transcriptase inhibitors.

DOSES OF FOSPHENYTOIN ARE ALWAYS EXPRESSED IN TERMS OF MILLIGRAMS OF PHENYTOIN SODIUM EQUIVALENTS (mg PE). 1 mg PE IS EQUIVALENT TO 1 mg PHENYTOIN SODIUM. DO NOT, THEREFORE, MAKE ANY ADJUSTMENT IN THE RECOMMENDED DOSES WHEN SUBSTITUTING FOSPHENYTOIN FOR PHENYTOIN SODIUM OR VICE VERSA. FOR EXAMPLE, IF A PATIENT IS RECEIVING 1000 mg PE OF FOSPHENYTOIN, THAT IS EQUIVALENT TO 1000 mg OF PHENYTOIN SODIUM. The following warnings are based on experience with fosphenytoin or phenytoin.

Dosing Errors Do not confuse the amount of drug to be given in PE with the concentration of the drug in the vial. Medication errors associated with fosphenytoin have resulted in patients receiving the wrong dose of fosphenytoin. Fosphenytoin is marketed in 2 mL vials containing a total of 100 mg PE and 10 mL vials containing a total of 500 mg PE. The concentration of each vial is 50 mg PE/mL. Errors have occurred when the concentration of the vial (50 mg PE/mL) was misinterpreted to mean that the total content of the vial was 50 mg PE.

These errors have resulted in two- or ten-fold overdoses of fosphenytoin since each vial actually contains a total of 100 mg PE or 500 mg PE. In some cases, ten-fold overdoses were associated with fatal outcomes. To help minimize confusion, the prescribed dose of fosphenytoin should always be expressed in milligrams of phenytoin equivalents (mg PE) (see DOSAGE AND ADMINISTRATION ). Additionally, when ordering and storing fosphenytoin, consider displaying the total drug content (i.e., 100 mg PE/2 mL or 500 mg PE/10 mL) instead of concentration in computer systems, pre-printed orders, and automated dispensing cabinet databases to help ensure that total drug content can be clearly identified.