Administration of nitrofurantoin directly to infants under 1 month of age and in those with G-6-PD deficiency is contraindicated because of potential hemolysis in these infants. Nitrofurantoin doses in milk are low and it can be used while breastfeeding older infants, but it is best to avoid it in infants under 1 month of age and those with G-6-PD deficiency at any age.
The time of the peak amounts in milk depends on the food taken with the drug and the dosage form of the drug. Rapid-release capsules of nitrofurantoin macrocrystals reach their peak milk levels either 1 to 2 hours after the dose with food or 4 hours after a high-fat meal. The sustained-release product (Macrobid) has not been studied, but probably has a delayed peak milk time that would be difficult to predict in an individual mother.
In one early report, random samples of milk from several women in the first few days postpartum who were receiving 100 mg orally 4 times daily were tested for nitrofurantoin. Nitrofurantion was undetectable (<2 mg/L) in 20 samples measured.
A second study found milk levels ranging from 0 to 0.5 mg/L in 4 women (time postpartum not stated) 2 hours after a single dose of 200 mg of nitrofurantoin was given orally during therapy with 100 mg 4 times a day. In 5 others receiving 100 mg orally 4 times daily, no drug was detected in milk levels (assay limit not stated).
Six women who were 3 to 6 days postpartum were given 50 or 100 mg of macrocrystalline nitrofurantoin orally 3 times a day. Nitrofurantoin was undetectable (<10 mcg/L) in all women before the first dose of the second day of administration with breakfast (fat content not stated). Peak milk levels occurred 1 to 2 hours after the dose. Mothers taking the 50 mg dose had an average of 0.49 mg/L (range 0.2 to 0.7 mg/L) in milk 3 hours after the dose and those given 100 mg had milk levels of 1.19 mg/L (range 0.62 to 2.22 mg/L) in milk at 3 hours. The authors calculated that between 0.06 and 0.28% of a dose was excreted into milk during the 6 hours after a dose.
Four women who were 8 to 26 weeks postpartum received a single 100 mg dose of nitrofurantoin macrocrystals orally with a high-fat meal. Under these conditions, peak milk levels occurred 4 to 6 hours after the dose. Peak levels averaged 2.7 mg/L (range 2.2 to 3.2 mg/L). Milk levels were higher than serum levels and much higher than predicted at all times, indicating active transport into milk. Nevertheless, an exclusively breastfed infant would receive only 0.2 mg/kg/day or about 6% of the weight-adjusted maternal dosage.
Relevant published information was not found as of the revision date.
Effects in Breastfed Infants:
In a prospective follow-up study, 6 nursing mothers reported taking nitrofurantoin (dosage and dosage form not specified). Two mothers reported diarrhea in their infants. No rashes or candidiasis were reported among the exposed infants.
Possible Effects on Lactation:
In a prospective follow-up study, 1 of 6 nursing mothers who took nitrofurantoin (dosage unspecified) reported a decrease in milk supply. It is not known if there was a causal relationship.
1. Hosbach RE, Foster RB. Absence of nitrofurantoin from human milk. JAMA. 1967;202:1057. Letter. PMID:6072610 2. Varsano I, Fischl J, Shochet SB. The excretion of orally ingested nitrofurantoin in human milk. J Pediatr. 1973;82:886-7. PMID:4735457 3. Pons G, Rey E, Richard MO et al. Nitrofurantoin excretion in human milk. Dev Pharmacol Ther. 1990;14:148-52. PMID:2364853 4. Gerk PM, Kuhn RJ, Desai NS et al. Active transport of nitrofurantoin into human milk. Pharmacotherapy. 2001;21:669-75. PMID:11401180 5. Ito S, Blajchman A, Stephenson M et al. Prospective follow-up of adverse reactions in breast-fed infants exposed to maternal medication. Am J Obstet Gynecol. 1993;168:1393-9. PMID:8498418
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