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Fosphenytoin Pregnancy and Breastfeeding Warnings

Fosphenytoin is also known as: Cerebyx

Fosphenytoin Pregnancy Warnings

Fosphenytoin has been assigned to pregnancy category D by the FDA. Animal studies with fosphenytoin have revealed evidence of abnormalities in embryo-fetal development. An increased risk of congenital abnormalities ("fetal hydantoin syndrome") has been associated with the use of phenytoin (the active metabolite of fosphenytoin) in epileptic women during pregnancy. Additionally, neonatal coagulation defects (reversible with vitamin K administration) have been reported postpartum. There are no controlled data in human pregnancy. Fosphenytoin should only be given during pregnancy when there are no alternatives and benefit outweighs risk.

The patient should be informed of the potential harm to the neonate if fosphenytoin is administered during pregnancy. The overall incidence of neonate malformations for offspring of mothers treated with antiseizure medications (phenytoin and/or others) is approximately 10%, or two- to threefold the incidence in the general population (although a definite causal relationship has not been established). Altered phenytoin pharmacokinetics during pregnancy may decrease the maternal seizure threshold. Measurement of plasma phenytoin concentrations may be valuable in adjusting dosages during pregnancy.

Fosphenytoin Breastfeeding Warnings

It is known that phenytoin (the major active metabolite of fosphenytoin) is excreted into human milk in small quantities. Typical doses given to a nursing mother would be expected to result in very small infant doses (less than 5% of a typical dose for most infants).

There are no data on the excretion of fosphenytoin into human milk. The manufacturer does not recommend that fosphenytoin be administered to women who are breast-feeding. The American Academy of Pediatrics classifies phenytoin as a drug which is "usually compatible with breast-feeding." The Academy notes one case of methemoglobinemia as a cause of possible concern.

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