Is Metronidazole safe while breastfeeding?

Effects on the breastfed infant

None of ten 5-day-old infants who were breastfed every 4 hours after a single maternal 200 mg oral dose of metronidazole had any signs of oral or gastrointestinal upset during the 12-hour study period.[ 5 ] Sixteen newborn breastfed infants (aged 0 to 22 days) of mothers receiving 200 mg or 400 mg of oral metronidazole 3 times daily reportedly suffered no observable adverse reactions during the 9 days of the study.[ 8 ] A case of diarrhea and secondary lactose intolerance was possibly caused by metronidazole in breastmilk transmitted to the infant in the early neonatal period.[ 12 ] In a controlled, comparative study, 35 newborn infants were monitored for 10 days during maternal therapy with metronidazole and another antibiotic (33 ampicillin, 1 erythromycin and 1 cephalexin) for postpartum infection or prophylaxis. Dosages and routes of administration were not stated, but some mothers received the drugs intravenously initially and then were switched to oral therapy. Compared to infants of mothers who received ampicillin alone or no antibiotics, more infants exposed to metronidazole and ampicillin had very loose stools than in the other groups, especially when the drugs were given intravenously. More frequent and heavier growth of Candida species was found in the oral and perianal swabs of metronidazole-exposed infants, but this did not quite reach statistical significance (p=0.053). One infant exposed to metronidazole and ampicillin developed oral thrush. No differences were found between the groups in diaper rash, feeding problems or weight gain to the time of discharge.[ 9 ]

Effects on milk supply

Relevant published information was not found as of the revision date.

Levels in milk

Maternal Levels. Ten women were given a single oral dose of metronidazole 200 mg at 5 days postpartum. Milk levels averaged 3.4 mg/L at 4 hours, 2.8 mg/L at 8 hours and 1.3 mg/L at 12 hours (5 women) after the dose.[ 5 ] Seventeen mothers in a randomized study received oral metronidazole 200 mg 3 times daily for 7 days postpartum. Milk metronidazole levels taken at unstated times on day 6 averaged 4.7 mg/L (range 1.1 to 15.2 mg/L).[ 6 ] Three women were given a single 2 gram oral dose of metronidazole for trichomoniasis. Average milk levels were 45.8 mg/L at 2 hours after the dose, 27.9 mg/L at 8 hours after the dose, 19.1 mg/L at 12 hours after the dose, 12.6 mg/L at 18 hours (2 women) and 3.5 mg/L at 36 hours after the dose (2 women). The authors estimated that the infants would receive a total of 25.3 mg over the 48 hours following this dose.[ 7 ] Fifteen women received 200 mg (n = 11) or 400 mg (n = 4) of metronidazole orally 3 times a day for postpartum endometritis 0 to 22 days postpartum. Single milk samples taken after 1 to 9 days of therapy and from 30 minutes to 4 hours after a 200 mg dose contained 1.6 to 12.2 mg/L of metronidazole and 1.1 to 3.8 mg/L of hydroxymetronidazole. Milk samples taken 2 to 3 hours after a 400 mg dose contained 11.6 to 18 mg/L of metronidazole and 2.4 to 6.3 mg/L of hydroxymetronidazole.[ 8 ] Twelve women taking oral metronidazole 400 mg 3 times daily at an average of 4.3 days postpartum had milk samples taken on days 3 and 4 postpartum. Milk levels of metronidazole averaged 15.5 mg/L at 2 hours after the dose, 12.9 mg/L at 4 hours after the dose, 10.6 mg/L at 6 hours after the dose, and 9.1 mg/L at 8 hours after the dose. Milk levels of hydroxymetronidazole averaged 5.5 mg/L at 2 hours after the dose, 5.7 mg/L at 4 hours after the dose, 5.6 mg/L at 6 hours after the dose, and 5.5 mg/L at 8 hours after the dose. The authors estimated that a breastfed neonate ingesting 500 mL of milk daily with this maternal dosage would receive l

Alternatives LactMed lists

• Clindamycin