May 27 2022


Risks to the infant

Several studies of few patients, with standard doses of metronidazole, have not detected changes in neonates. However, there have reported cases of candida infection and diarrhea after administration of metronidazole to the mother. Some data suggest that the presence of the fungus Candida albicans, both in the mouth and in the rectum is more common in children exposed to metronidazole through breastfeeding.

American Academy of Pediatrics recommends discontinue breastfeeding for 12-24 hours after administration of a single dose of 2 g metronidazole (STAT dose), to allow drug levels in milk to fall enough. A kinetic study has shown that the drug concentration in milk decreases from 45.8 mg/L at two hours after its administration until 12.6 mg/L at 18 hours after taking it.

Influence on lactation

In two studies with a small number of patients, in infants whose mothers received oral metronidazole 1200 mg a day in three doses, were recorded average levels of metronidazole and its hydroxy metabolite between 4 and 32% of the metronidazole concentration of the mother and between 8 and 96% of that of hydroxymetronidazole.

In a group of twelve women who received the standard dose of 400 mg metronidazole every eight hours, the concentration of the drug in milk decreased from 15.5 mg/L at two hours after the intake of metronidazole to 9.1 mg/L at eight hours. According to these data, a 5 kg baby exclusively breastfed receive approximately 7 to 11 mg/day of metronidazole through breastfeeding. A therapeutic dosage in the same child would need 50 to 100 mg of metronidazole per day. Some authors estimate that the dose received by the infant would not exceed 10% of therapeutics.


The final effect on the infant is unknown, but the baby breastfed by mothers receiving metronidazole by any route, including topical, must be controlled.

Metronidazole has shown to be potentially carcinogenic in animals, as well as genotoxic and mutagenic in bacteria, so metronidazole administration to the mother, even admitting its necessity, must be very well argued and could not exist better alternative. The issue is controversial and there is no an unanimous opinion. For some authors, metronidazole would be just the opposite. There is not any in-depth study on the subject.


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Warning of the manufacturer:

Metronidazole is excreted in human milk and should therefore be avoided unnecessary administration of the drug during lactation.