Fosphenytoin is the prodrug for its active metabolite, phenytoin.3280 Fosphenytoin sodium is available as a solution containing 50 mg phenytoin sodium equivalents (PE)/mL in single-dose 2-mL (100-mg) and 10-mL (500-mg) vials.3280 Each mL of solution also contains tromethamine (TRIS) buffer along with hydrochloric acid or sodium hydroxide to adjust the pH in water for injection.3280
CAUTION: Care should be taken to avoid confusion between the two different forms (i.e., fosphenytoin sodium and phenytoin sodium) to prevent dosing errors.3280
Units
Each 1.5 mg of fosphenytoin sodium is equivalent to phenytoin sodium 1 mg and is referred to as 1 mg of phenytoin sodium equivalents (PE).3280 The amount and concentration of fosphenytoin sodium are expressed in terms of the equivalent mass of phenytoin sodium.3280 Manufacturers indicate that this avoids the need to perform conversions between the two forms based on molecular weight; however, it necessitates that all prescribing, preparation, and dosing be consistently expressed in terms of PE to avoid dosing errors that could result from confusion between the two forms.3280
pH
From 8.6 to 93280 or 8.3 to 9.3.3281
Phosphate Content
Each 1 mg PE contains 0.0037 mmol phosphate.3280
Trade Name(s)
Cerebyx
Fosphenytoin sodium is dosed in terms of phenytoin sodium equivalents (PE).3280
CAUTION: Care should be taken to ensure that all prescribing, preparation, and dosing is performed using the correct units and that any confusion between the two forms (i.e., fosphenytoin sodium and phenytoin sodium) is avoided.3280
Fosphenytoin sodium is administered intravenously.3280 For intravenous infusion, fosphenytoin sodium must be diluted in dextrose 5% or sodium chloride 0.9% to a concentration ranging from 1.5 mg PE/mL to a maximum of 25 mg PE/mL.3280 The drug also has been administered intramuscularly in certain situations when intravenous access is not possible.3280
For the treatment of status epilepticus in adult patients, a loading dose of fosphenytoin sodium should be administered by intravenous infusion at a rate of 100 to 150 mg PE/min; the rate of administration must not exceed 150 mg PE/min.3280 The intramuscular route of administration generally should not be used in the treatment of status epilepticus.3280 For non-emergent situations in adult patients in which fosphenytoin sodium is indicated, the loading dose may be administered intravenously or intramuscularly.3280 For non-emergent indications, intravenous fosphenytoin sodium infusion should be administered more slowly.3280 The rate of administration of maintenance doses in adults also should not exceed 150 mg PE/min.3280
For the treatment of status epilepticus in pediatric patients, a loading dose of fosphenytoin sodium should be administered by intravenous infusion at a rate of 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower); the rate of administration must not exceed 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower).3280 For non-emergent indications, intravenous fosphenytoin sodium infusion should be administered more slowly.3280 For non-emergent situations in pediatric patients in which fosphenytoin sodium is indicated, the loading dose should be administered intravenously at a rate of 1 to 2 mg PE/kg/min (or 150 mg PE/min, whichever is slower).3280 Following administration of a loading dose, maintenance doses in pediatric patients should be administered at a rate of 1 to 2 mg PE/kg/min (or 100 mg PE/min, whichever is slower).3280 The intramuscular route of administration generally should not be used in pediatric patients.3280
Purple glove syndrome, characterized by edema, discoloration, and pain distal to the site of infusion, has been reported following intravenous administration of fosphenytoin sodium through a peripheral vein and may or may not be associated with extravasation.3280
Fosphenytoin sodium injection is a clear, colorless to pale yellow solution.3280 Intact vials should be stored under refrigeration at 2 to 8°C.3280 Storage at room temperature should not exceed 48 hours.3280
Fosphenytoin sodium injection solution should be visually inspected for particulate matter and discoloration prior to administration.3280 Any unused portions should be discarded.3280
Freezing Solutions
Fosphenytoin sodium (Parke-Davis) 1, 8, and 20 mg PE/mL in dextrose 5% (Baxter) and sodium chloride 0.9% (Baxter) in PVC containers and undiluted fosphenytoin sodium 50 mg PE/mL were packaged in 3-mL polypropylene syringes sealed with tip caps (Becton Dickinson). The samples were frozen at -20°C. Little or no loss occurred after 30 days of frozen storage followed by 7 days at 4 or 25°C. Stability also was maintained if the thawed samples that had been stored at 25°C were returned to the freezer for an additional 7 days.2083
Syringes
Fosphenytoin sodium (Parke-Davis) 50 mg PE/mL was packaged in 3-mL polypropylene syringes with syringe caps (Becton Dickinson) and stored at -20, 4, and 25°C. The samples stored at 4 and 25°C exhibited little or no loss of fosphenytoin sodium in 30 days. The samples stored at -20°C also showed little or no loss of fosphenytoin sodium after 30 days of storage followed by 7 days at 4°C or at 25°C. Stability was maintained if the thawed samples that had been stored at 25°C were returned to the freezer for an additional 7 days.2083
For a list of references cited in the text of this monograph, search the monograph titled References.