DOSES OF FOSPHENYTOIN SODIUM INJECTION, USP ARE EXPRESSED AS THEIR PHENYTOIN SODIUM EQUIVALENTS IN THIS LABELING (PE=phenytoin sodium equivalent).
DO NOT, THEREFORE, MAKE ANY ADJUSTMENT IN THE RECOMMENDED DOSES WHEN SUBSTITUTING FOSPHENYTOIN SODIUM INJECTION, USP FOR PHENYTOIN SODIUM OR VICE VERSA.The following warnings are based on experience with Fosphenytoin Sodium Injection, USP or phenytoin.Status Epilepticus Dosing RegimenDo not administer Fosphenytoin Sodium Injection, USP at a rate greater than 150 mg PE/min.The dose of IV Fosphenytoin Sodium Injection, USP (15 to 20 mg PE/kg) that is used to treat status epilepticus is administered at a maximum rate of 150 mg PE/min.
The typical Fosphenytoin Sodium Injection, USP infusion administered to a 50 kg patient would take between 5 and 7 minutes.
Note that the delivery of an identical molar dose of phenytoin using parenteral Dilantin or generic phenytoin sodium injection cannot be accomplished in less than 15 to 20 minutes because of the untoward cardiovascular effects that accompany the direct intravenous administration of phenytoin at rates greater than 50 mg/min.If rapid phenytoin loading is a primary goal, IV administration of Fosphenytoin Sodium Injection, USP is preferred because the time to achieve therapeutic plasma phenytoin concentrations is greater following IM than that following IV administration (see DOSAGE AND ADMINISTRATION).Withdrawal Precipitated Seizure, Status EpilepticusAntiepileptic drugs should not be abruptly discontinued because of the possibility of increased seizure frequency, including status epilepticus.
When, in the judgement of the clinician, the need for dosage reduction, discontinuation, or substitution of alternative antiepileptic medication arises, this should be done gradually.
However, in the event of an allergic or hypersensitivity reaction, rapid substitution of alternative therapy may be necessary.
In this case, alternative therapy should be an antiepileptic drug not belonging to the hydantoin chemical class.Cardiovascular DepressionHypotension may occur, especially after IV administration at high doses and high rates of administration.
Following administration of phenytoin, severe cardiovascular reactions and fatalities have been reported with atrial and ventricular conduction depression and ventricular fibrillation.
Severe complications are most commonly encountered in elderly or gravely ill patients.
Therefore, careful cardiac monitoring is needed when administering IV loading doses of Fosphenytoin Sodium Injection, USP.
Reduction in rate of administration or discontinuation of dosing may be needed.Fosphenytoin Sodium Injection, USP should be used with caution in patients with hypotension and severe myocardial insufficiency.RashFosphenytoin Sodium Injection, USP should be discontinued if a skin rash appears. If the rash is exfoliative, purpuric, or bullous, or if lupus erythematosus, Stevens-Johnson syndrome, or toxic epidermal necrolysis is suspected, use of this drug should not be resumed and alternative therapy should be considered.
If the rash is of a milder type (measles-like or scarlatiniform), therapy may be resumed after the rash has completely disappeared. If the rash recurs upon reinstitution of therapy, further Fosphenytoin Sodium Injection, USP or phenytoin administration is contraindicated.Hepatic InjuryCases of acute hepatotoxicity, including infrequent cases of acute hepatic failure, have been reported with phenytoin.
These incidents have been associated with a hypersensitivity syndrome characterized by fever, skin eruptions, and lymphadenopathy, and usually occur within the first 2 months of treatment.
Other common manifestations include jaundice, hepatomegaly, elevated serum transaminase levels, leukocytosis, and eosinophilia.
The clinical course of acute phenytoin hepatotoxicity ranges from prompt recovery to fatal outcomes.
In these patients with acute hepatotoxicity, Fosphenytoin Sodium Injection, USP should be immediately discontinued and not readministered.Hemopoietic SystemHemopoietic complications, some fatal, have occasionally been reported in association with administration of phenytoin.
These have included thrombocytopenia, leukopenia, granulocytopenia, agranulocytosis, and pancytopenia with or without bone marrow suppression.There have been a number of reports that have suggested a relationship between phenytoin and the development of lymphadenopathy (local or generalized), including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin's disease.
Although a cause and effect relationship has not been established, the occurrence of lymphadenopathy indicates the need to differentiate such a condition from other types of lymph node pathology.
Lymph node involvement may occur with or without symptoms and signs resembling serum sickness, e.g., fever, rash, and liver involvement.
In all cases of lymphadenopathy, follow-up observation for an extended period is indicated and every effort should be made to achieve seizure control using alternative antiepileptic drugs.Alcohol UseAcute alcohol intake may increase plasma phenytoin concentrations while chronic alcohol use may decrease plasma concentrations.Usage in PregnancyClinical:Risks to Mother.
An increase in seizure frequency may occur during pregnancy because of altered phenytoin pharmacokinetics. Periodic measurement of plasma phenytoin concentrations may be valuable in the management of pregnant women as a guide to appropriate adjustment of dosage (see PRECAUTIONS, Laboratory Tests).
However, postpartum restoration of the original dosage will probably be indicated.Risks to the Fetus.
If this drug is used during pregnancy, or if the patient becomes pregnant while taking the drug, the patient should be apprised of the potential harm to the fetus.Prenatal exposure to phenytoin may increase the risks for congenital malformations and other adverse developmental outcomes.
Increased frequencies of major malformations (such as orofacial clefts and cardiac defects), minor anomalies (dysmorphic facial features, nail and digit hypoplasia), growth abnormalities (including microcephaly), and mental deficiency have been reported among children born to epileptic women who took phenytoin alone or in combination with other antiepileptic drugs during pregnancy.
There have also been several reported cases of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy.
The overall incidence of malformations for children of epileptic women treated with antiepileptic drugs (phenytoin and/or others) during pregnancy is about 10%, or two-to three-fold that in the general population.
However, the relative contributions of antiepileptic drugs and other factors associated with epilepsy to this increased risk are uncertain and in most cases it has not been possible to attribute specific developmental abnormalities to particular antiepileptic drugs.Patients should consult with their physicians to weigh the risks and benefits of phenytoin during pregnancy.Postpartum Period.
A potentially life-threatening bleeding disorder related to decreased levels of vitamin K-dependent clotting factors may occur in newborns exposed to phenytoin in utero.
This drug-induced condition can be prevented with vitamin K administration to the mother before delivery and to the neonate after birth.Preclinical: Increased frequencies of malformations (brain, cardiovascular, digit, and skeletal anomalies), death, growth retardation, and functional impairment (chromodacryorrhea, hyperactivity, circling) were observed among the offspring of rats receiving fosphenytoin during pregnancy.
Most of the adverse effects on embryo-fetal development occurred at doses of 33 mg PE/kg or higher (approximately 30% of the maximum human loading dose or higher on a mg/m2 basis), which produced peak maternal plasma phenytoin concentrations of approximately 20 mcg/mL or greater.
Maternal toxicity was often associated with these doses and plasma concentrations, however, there is no evidence to suggest that the developmental effects were secondary to the maternal effects.
The single occurrence of a rare brain malformation at a non-maternotoxic dose of 17 mg PE/kg (approximately 10% of the maximum human loading dose on a mg/m2 basis) was also considered drug-induced.
The developmental effects of fosphenytoin in rats were similar to those which have been reported following administration of phenytoin to pregnant rats.No effects on embryo-fetal development were observed when rabbits were given up to 33 mg PE/kg of fosphenytoin (approximately 50% of the maximum human loading dose on a mg/m2 basis) during pregnancy.Increased resorption and malformation rates have been reported following administration of phenytoin doses of 75 mg/kg or higher (approximately 120% of the maximum human loading dose or higher on a mg/m2 basis) to pregnant rabbits.