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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.

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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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References for pregnancy information

  1. Paulson GW, Paulson RB "Teratogenic effects of anticonvulsants." Arch Neurol 38 (1981): 140-3
  2. Dam M, Christiansen J, Munck O, Mygind KI "Antiepileptic drugs: metabolism in pregnancy." Clin Pharmacokinet 4 (1979): 53-62
  3. Knott C, Williams CP, Reynolds F "Phenytoin kinetics during pregnancy and the puerperium." Br J Obstet Gynaecol 93 (1986): 1030-7
  4. Dean M, Stock B, Patterson RJ, Levy G "Serum protein binding of drugs during and after pregnancy in humans." Clin Pharmacol Ther 28 (1980): 253-61
  5. Kochenour NK, Emery MG, Sawchuk RJ "Phenytoin metabolism in pregnancy." Obstet Gynecol 56 (1980): 577-82
  6. "Teratogenic risks of antiepileptic drugs." Br Med J 283 (1981): 515-6
  7. Lander CM, Smith MT, Chalk JB, et al "Bioavailability and pharmacokinetics of phenytoin during pregnancy." Eur J Clin Pharmacol 27 (1984): 105-10
  8. Steen B, Rane A, Lonnerholm G, Falk O, Elwin CE, Sjoqvist F "Phenytoin excretion in human breast milk and plasma levels in nursed infants." Ther Drug Monit 4 (1982): 331-4
  9. "Product Information. Cerebyx (fosphenytoin)." Parke-Davis, Morris Plains, NJ.
  10. Monson RR, Rosenberg L, Hartz SC, et al "Diphenylhydantoin and selected congenital malformations." N Engl J Med 289 (1973): 1049-52
  11. Eadie MJ, McKinnon GE, Dickinson RG, et al "Phenytoin metabolism during pregnancy." Eur J Clin Pharmacol 43 (1992): 389-92

References for breastfeeding information

  1. "Product Information. Cerebyx (fosphenytoin)." Parke-Davis, Morris Plains, NJ.
  2. Roberts RJ, Blumer JL, Gorman RL, et al "American Academy of Pediatrics Committee on Drugs: Transfer of drugs and other chemicals into human milk." Pediatrics 84 (1989): 924-36

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