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Fosphenytoin Pregnancy and Breastfeeding Warnings

Medically reviewed by Last updated on May 20, 2022.

Fosphenytoin is also known as: Cerebyx, Sesquient

Fosphenytoin Pregnancy Warnings

Benefit should outweigh risk

US FDA pregnancy category: Not assigned

Risk Summary: Fosphenytoin is the prodrug of phenytoin; prenatal exposure to phenytoin may increase the risks for congenital malformations and other adverse developmental outcomes; meta-analyses using data from published observational studies and registries have estimated an approximately 2.4-fold increased risk for any major malformation in children with prenatal phenytoin exposure compared to controls. There are significant risks to mother and fetus with uncontrolled seizures.

-This drug should only be used in women of childbearing potential, women planning pregnancy, and pregnant women, when there is a clear clinical need and when she is made aware of the risks of use during pregnancy; additionally, this drug may cause failure of hormonal contraceptives and women of childbearing potential should be counseled regarding effective contraception while receiving this drug.
-Increased seizure frequency may occur during pregnancy because of altered phenytoin pharmacokinetics; serum phenytoin concentrations should be closely monitored.
-A potentially life-threatening bleeding disorder may occur in newborns exposed to phenytoin in utero; this drug-induced condition can be prevented by administration of Vitamin K to the mother before delivery and to the neonate after birth.
-Pregnancy Exposure Registry: Pregnant patients should be encourage to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry; Phone: 1-888-233-2334; website:

Malformations including craniofacial, cardiovascular, neural, limb, and digit abnormalities, have been observed in rats, rabbits, and mice at doses as low as 100, 75, and 12.5 mg/kg, respectively. Malformations such as orofacial clefts, cardiac defects, dysmorphic facial features, nail and digit hypoplasia, and growth abnormalities (including microcephaly) have been reported in children born to mothers who took phenytoin during pregnancy. Fetal hydantoin syndrome, a pattern of abnormalities including a dysmorphic skull and facial features, nail and digit hypoplasia, growth abnormalities (including microcephaly), and cognitive deficits has been associated with the use of phenytoin alone or in combination with other antiepileptic drugs during pregnancy. There have been several case reports of malignancies, including neuroblastoma, in children whose mothers received phenytoin during pregnancy. There are no controlled data in human pregnancy.

US FDA pregnancy category Not Assigned: The US FDA has amended the pregnancy labeling rule for prescription drug products to require labeling that includes a summary of risk, a discussion of the data supporting that summary, and relevant information to help health care providers make prescribing decisions and counsel women about the use of drugs during pregnancy. Pregnancy categories A, B, C, D, and X are being phased out.

See references

Fosphenytoin Breastfeeding Warnings

This drug is rapidly metabolized in the body to the active drug phenytoin. Because of the low levels of phenytoin in breastmilk, amounts ingested by the infant are small and usually cause no difficulties when used alone except for rare idiosyncratic reactions. Breastfeeding during phenytoin monotherapy does not appear to adversely affect infant growth or development. Combination therapy with sedating anticonvulsants or psychotropics may result in infant sedation or withdrawal reactions.

Benefit should outweigh risk

Excreted into human milk: Unknown
Excreted into animal milk: Data not available

-Fosphenytoin is a prodrug of phenytoin; phenytoin is excreted in breastmilk.
-The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for this drug and any potential adverse effects to the breastfed infant from the drug or from the underlying maternal condition.

See references

References for pregnancy information

  1. Monson RR, Rosenberg L, Hartz SC, et al. "Diphenylhydantoin and selected congenital malformations." N Engl J Med 289 (1973): 1049-52
  2. Eadie MJ, McKinnon GE, Dickinson RG, et al. "Phenytoin metabolism during pregnancy." Eur J Clin Pharmacol 43 (1992): 389-92
  3. Knott C, Williams CP, Reynolds F "Phenytoin kinetics during pregnancy and the puerperium." Br J Obstet Gynaecol 93 (1986): 1030-7
  4. Kochenour NK, Emery MG, Sawchuk RJ "Phenytoin metabolism in pregnancy." Obstet Gynecol 56 (1980): 577-82
  5. Dam M, Christiansen J, Munck O, Mygind KI "Antiepileptic drugs: metabolism in pregnancy." Clin Pharmacokinet 4 (1979): 53-62
  6. Lander CM, Smith MT, Chalk JB, et al. "Bioavailability and pharmacokinetics of phenytoin during pregnancy." Eur J Clin Pharmacol 27 (1984): 105-10
  7. Paulson GW, Paulson RB "Teratogenic effects of anticonvulsants." Arch Neurol 38 (1981): 140-3
  8. "Teratogenic risks of antiepileptic drugs." Br Med J 283 (1981): 515-6
  9. "Product Information. Cerebyx (fosphenytoin)." Parke-Davis (2001):
  10. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  11. "Product Information. Sesquient (fosphenytoin)." Emergent BioSolutions Inc. (2021):

References for breastfeeding information

  1. "Product Information. Cerebyx (fosphenytoin)." Parke-Davis (2001):
  2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  3. United States National Library of Medicine "Toxnet. Toxicology Data Network." (2013):
  4. "Product Information. Sesquient (fosphenytoin)." Emergent BioSolutions Inc. (2021):

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.