Skip to Content
Here’s what to ask a doctor about hereditary angioedema

Metronidazole Pregnancy and Breastfeeding Warnings

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

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 Comments: -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 Comments: -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. "Product Information. Flagyl (metronidazole)." Searle, Skokie, IL.
  4. CDC. Centers for Disease Control and Prevention "Sexually Transmitted Diseases Treatment Guidelines, 2015. Available from: URL:" (June 5, 2015):

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 -]):

Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Wolters Kluwer Health and is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This drug information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate that the drug or combination is safe, effective, or appropriate for any given patient. Multum Information Services, Inc. does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. Copyright 2000-2008 Multum Information Services, Inc. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse, or pharmacist.