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Metronidazole Pregnancy and Breastfeeding Warnings

Metronidazole is also known as: Flagyl, Flagyl 375, Flagyl ER, Flagyl IV, Metro, Metro IV, Metryl, Protostat

Medically reviewed by Last updated on Oct 22, 2018.

Metronidazole Pregnancy Warnings

Animal studies have failed to reveal evidence of impaired fertility nor fetal harm at higher doses. However, fetotoxicity was observed in pregnant mice when this drug was administered intraperitoneally. This drug crosses the placenta and rapidly enters fetal circulation. Published data in more than 5000 pregnant women who used this drug during pregnancy (majority during the first trimester) included reports of increased risk of cleft lip, with or without cleft palate; however, these findings cannot be confirmed. The majority of studies did not show an increased risk for congenital anomalies or other adverse fetal outcomes. There are no controlled data in human pregnancy.

AU TGA pregnancy category B2: Drugs which have been taken by only a limited number of pregnant women and women of childbearing age, without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals are inadequate or may be lacking, but available data show no evidence of an increased occurrence of fetal damage.

US FDA pregnancy category B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

Bacterial Vaginosis and Trichomoniasis: Use is contraindicated during the first trimester of pregnancy; according to some authorities, use is not recommended during the first trimester of pregnancy; use is not recommended unless clearly needed during the second and third trimesters of pregnancy

All Other Indications: Use is not recommended unless clearly needed; according to some authorities, use is not recommended in the first trimester

AU TGA pregnancy category: B2
US FDA pregnancy category: B

-According to some authorities, use for trichomoniasis in the second and third trimester should be reserved for those in whom local palliative treatment has been inadequate to control symptoms.
-The US CDC recommends treatment of trichomoniasis at any stage of pregnancy.

See references

Metronidazole Breastfeeding Warnings

Case reports regarding candida infections and diarrhea have been reported and a comparative trial suggests oral and rectal colonization with Candida might be more common in infants exposed to this drug. In one report, 3 women were given 2 g orally for trichomoniasis where the average milk levels were 45.8 mg/L at 2 hours, 27.9 mg/L at 8 hours, 19.1 mg/L at 12 hours, 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 an infant would receive a total of 25.3 mg over the 48 hours following the dose. In a separate report, 11 infants whose mothers were taking 600 mg orally daily had plasma metronidazole levels averaging 0.8 mg/L (range 0.3 to 1.4 mg/L) and hydroxymetronidazole levels averaging 0.4 mg/L (range 0.1 to 0.8 mg/L).

A decision should be made to discontinue breastfeeding or discontinue the drug, taking into account the importance of the drug to the mother.

Excreted into human milk: Yes

-This drug is secreted in breast milk in concentrations similar to those found in the plasma.
-Due to the potential for tumorigenicity in animal studies, a nursing mother may choose to pump and discard her milk during therapy and for 24 hours after therapy ends and feed her infant stored human milk or formula.
-Some sources recommend discontinuing breastfeeding for 12 to 24 hours after single-dose maternal treatment.

See references

References for pregnancy information

  1. Cerner Multum, Inc. "Australian Product Information." O 0
  2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  3. CDC. Centers for Disease Control and Prevention "Sexually Transmitted Diseases Treatment Guidelines, 2015. Available from: URL:" (June 5, 2015):
  4. "Product Information. Flagyl (metronidazole)." Searle, Skokie, IL.

References for breastfeeding information

  1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0
  2. "Product Information. Flagyl (metronidazole)." Searle, Skokie, IL.
  3. Cerner Multum, Inc. "Australian Product Information." O 0
  4. United States National Library of Medicine "Toxnet. Toxicology Data Network. Available from: URL:" ([cited 2013 -]):

Further information

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