Is Fosphenytoin safe while breastfeeding?
Here is what NIH LactMed, the U.S. National Library of Medicine's authority on medicines and breastfeeding, reports about Fosphenytoin. This is a summary of that source — not our own verdict.
Effects on the breastfed infant
A mother was taking phenobarbital 390 mg daily and phenytoin 400 mg daily during pregnancy and postpartum. Her infant was drowsy at birth, refused to suck and was given partial formula feeding. At 5 days of age, her infant was admitted to the hospital pale and collapsed with bruising, bleeding, and a decreased hemoglobin, thought to be due to methemoglobinemia. Breastfeeding was discontinued and the infant was given a transfusion which rapidly improved her condition. On day 10, the mother resumed breastfeeding the infant. Within 24 hours the infant was extremely sedated and refused to suck and was fed breastmilk with a spoon. The sedation persisted for 2 days until breastmilk was discontinued permanently because of a return of methemoglobinemia. The extreme sedation was probably due to phenobarbital in the milk and the methemoglobinemia was probably caused by the phenytoin.[ 12 ] One clinician reported that the breastfed infants of 28 mothers who were taking phenytoin 100 to 200 mg 3 times daily had no adverse reactions including drowsiness or lethargy.[ 13 ] No adverse effects were noted in the breastfed neonates of 2 mothers who were taking phenytoin 300 mg daily.[ 3 ] A 10-week-old breastfed infant whose mother was taking clemastine, phenytoin and carbamazepine was drowsy, refused to feed, was irritable, and had high-pitched crying.[ 14 ] These side effects were possibly caused by clemastine in breastmilk, but the other drugs could also have contributed. A probable case of drug-induced drowsiness occurred in a newborn whose mother was taking primidone, carbamazepine and phenytoin (dosages not stated). At day 30, breastfeeding was discontinued because of the drowsiness that occurred after each feeding and poor weight gain. The same group of researchers found that 15 partially breastfed infants whose mothers were taking various anticonvulsants, including phenytoin, gained weight at a slower rate during the first 5 days postpartum than did 75 infants of epileptic mo
Effects on milk supply
Relevant published information was not found as of the revision date.
Levels in milk
Fosphenytoin is rapidly metabolized to phenytoin, formaldehyde and phosphate after administration. Information on phenytoin during breastfeeding is listed below. In published reports of anticonvulsant use during breastfeeding, most women were taking a combination of anticonvulsants. Some other anticonvulsants (e.g., phenytoin, carbamazepine) stimulate the metabolism of other drugs including anticonvulsants, whereas others (e.g., valproic acid) inhibit the metabolism of other drugs. Therefore, the relationship of the maternal dosage to the concentration in breastmilk can be quite variable, making calculation of the weight-adjusted percentage of maternal dosage less meaningful than for other drugs in this database. Maternal Levels. Two women were taking phenytoin 300 mg daily (dosage details not reported) during pregnancy and postpartum. In one, milk levels ranged from 1.2 to 2.2 mg/L at various times on days 4 to 6 postpartum. The highest levels were reported on day 6. In the other, levels ranged from 1 to 2.6 mg/L on days 1 to 4 postpartum and was 1.3 mg/L on day 33 postpartum.[ 3 ] In a woman taking phenytoin 500 mg daily in 2 divided doses 12 hours apart, breastmilk phenytoin levels were 0.58 mg/L 3 hours after the morning dose and 0.26 mg/L 1 hour before the evening dose.[ 4 ] Eight phenytoin breastmilk levels were measured between days 3 and 32 postpartum at unstated times after the dose in an unstated number of women who were taking phenytoin and other anticonvulsants in unstated dosages. Phenytoin milk levels averaged 0.8 mg/L (range 0.5 to 1.4 mg/L), while maternal serum levels averaged 4.5 mg/L.[ 5 ] A mother who was taking phenytoin 200 mg twice daily had breastmilk phenytoin levels measured 5 times during days 2 to 4 postpartum. Milk levels ranged from trace to 2 mg/L.[ 6 ] Two mothers taking phenytoin during pregnancy and postpartum had breastmilk levels measured during the first week postpartum. One who was taking 300 mg daily had a milk level of 2.7 mg/
Alternatives LactMed lists
Source: NIH LactMed (National Library of Medicine).
Educational summary of an authoritative source — not medical advice. Never start, stop, or change a medicine while breastfeeding without confirming with your doctor.