Adult Dosing
Status Epilepticus
- Loading dose: 15-20 mg PE/kg IV at a rate of 100-150 mg PE/min
- Maintenance dose: 4-6 mg PE/kg/day IM/IV
Neurosurgery related seizures
- Loading dose: 10-20 mg PE/kg IM/IV at a rate not exceeding 150 mg PE/min
- Maintenance dose: 4-6 mg PE/kg/day IM/IV
Note:
- Fosphenytoin doses are expressed as phenytoin sodium equivalents (PE) to avoid the need to perform molecular weight-based adjustments when converting between fosphenytoin and phenytoin sodium doses
- Dilute in 5% dextrose injection or 0.9% sodium chloride injection, prior to IV infusion
Prophylaxis of seizures in subdural hematoma [Non-FDA Approved]
- Loading dose 15-20 mg/kg IV
Pediatric Dosing
- Safety and efficacy of fosphenytoin in pediatric patients have not been established
Seizure prophylaxis in Subarachnoid Hemorrhage [Non-FDA Approved]
- Loading dose (all ages): 15-20 mg/kg IV
- Max. dose: 1500 mg/24 hr
- Maintenance for seizure disorders:
- Neonate: Start with 5 mg/kg/24 hr IV divided q12 hr; usual range 5-8 mg/kg/24 hr IV divided q8-12 hr
- Infant/child: Start with 5 mg/kg/24 hr divided bid-tid IV; usual dose range (doses divided bid-tid):
- 6 mo-3 yr: 8-10 mg/kg/24 hr
- 4-6 yr: 7.5-9 mg/kg/24 hr
- 7-9 yr: 7-8 mg/kg/24 hr
- 10-16 yr: 6-7 mg/kg/24 hr
Prophylaxis of seizures in subdural hematoma [Non-FDA Approved]
- Loading dose 15-20 mg/kg IV
[Outline]
- Do not make any dose adjustments when substituting fosphenytoin for phenytoin, as doses of fosphenytoin are expressed as their phenytoin sodium equivalents
- IV administration of fosphenytoin is preferred over IM, when rapid phenytoin loading is a primary goal because the time to achieve therapeutic plasma phenytoin concentrations is greater following IM than IV
- Do not discontinue antiepileptic drugs abruptly, as sudden withdrawal may precipitate seizure or status epilepticus. If there is need for dosage reduction, discontinuation, or substitution of alternative antiepileptic medication arises, it should be done gradually
- Hypotension has been reported, especially after IV administration at high doses and high rates of administration
- Severe cardiovascular reactions and fatalities have been reported with atrial and ventricular conduction depression and ventricular fibrillation. Careful cardiac monitoring is needed when administering IV loading doses of fosphenytoin. Reduce the rate of administration or discontinue the drug if such reaction occurs
- Discontinue therapy on development of skin rash. On suspicion of exfoliative, purpuric, or bullous rash or lupus erythematosus or Stevens-Johnson syndrome, do not resume the use of this drug and consider alternative therapy. If the rash is of a milder type (measles-like or scarlatiniform) therapy may be resumed after complete disappearance of rash. On recurrence of rash upon reinstitution of therapy, further phenytoin medication is contraindicated
- Acute hepatotoxicity associated with a hypersensitivity syndrome, characterized by fever, skin eruptions, lymphadenopathy, jaundice, hepatomegaly, elevated serum transaminase levels, leukocytosis, and eosinophilia has been reported with phenytoin. Immediately discontinue and do not readminister fosphenytoin if acute hepatotoxicity occurs
- Hemopoietic complications including thrombocytopenia, leukopenia, granulocytopenia, agranulocytosis, and pancytopenia with or without bone marrow suppression have been reported with administration of phenytoin
- Lymphadenopathy (local or generalized) including benign lymph node hyperplasia, pseudolymphoma, lymphoma and Hodgkin’s Disease may occur. Involvement of lymph nodes may occur with or without symptoms and signs resembling serum sickness. Conduct follow-up observation for an extended period and make efforts to achieve seizure control using alternative antiepileptic drugs for all cases of lymphadenopathy
- Increased phenytoin serum levels may occur with acute alcoholic intake while serum levels may decrease with chronic alcoholic use
- Higher incidence of birth defects may occur in children born to women using this drug. Avoid discontinuation of treatment in patients in whom the drug is administered to prevent major seizures, as strong possibility of precipitating status epilepticus with attendant hypoxia and threat to life exists. Discontinuation of the drug may be considered prior to and during pregnancy in individual cases where the severity and frequency of the seizure disorder are such that the removal of medication does not pose a serious threat to the patient; however it cannot be confirmed with any confidence that even minor seizures do not pose some hazard to the developing embryo or fetus. Weigh such considerations in treating or counseling epileptic women of childbearing potential
- Increased incidence of congenital malformation, such as cleft lip/palate and heart malformations in children of women receiving phenytoin have occurred. Reports also suggest that fetal hydantoin syndrome may also develop. Malignancies, including neuroblastoma may also occur in children whose mothers received phenytoin during pregnancy. Periodically measure serum phenytoin levels for the management of a pregnant epileptic patient as a guide to an appropriate adjustment of dosage
- Neonatal coagulation defects may occur within the first 24 hours in babies born to epileptic mothers receiving this drug. Administer Vitamin K to the mothers before and to the neonate after birth to prevent or correct such defect
- Severe burning, itching, and/or paresthesia has been reported. Slowing or temporarily stopping the infusion can lessen the occurrence and intensity of the discomfort
- Fosphenytoin can cause phosphate load, hence use cautiously in patients who require phosphate restriction, such as those with severe renal impairment
- Hyperglycemia may occur. This drug may also raise the serum glucose level in diabetic patients
- Delirium, psychosis, encephalopathy or rarely irreversible cerebellar dysfunction may occur due to sustained serum levels of phenytoin above optimal range. Consider dose reduction of phenytoin on excessive plasma levels and termination on persistence of symptoms
- This drug is not indicated for seizures due to hypoglycemic or other metabolic causes. Perform appropriate diagnostic procedures as indicated
Cautions: Use cautiously in
- Renal impairment
- Hepatic impairment
- Hypotension
- Severe myocardial insufficiency
- Cardiac disease
- Diabetes mellitus
- Porphyria
- Alcohol use
- Geriatric population
- Phosphate restriction
Pregnancy Category:D
Breastfeeding: It is not known whether fosphenytoin is excreted in human milk; however phenytoin is excreted in breastmilk in small amounts. Use not recommended according to manufacturer's data.
