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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

Metronidazole Pregnancy Warnings

Animal studies have failed to reveal evidence of fetal harm, except when the drug was administered intraperitoneally. There are no controlled data in human pregnancy. Metronidazole crosses the placental barrier; effects on human fetal organogenesis are not known. Published data from case-control studies, cohort studies, and 2 meta-analyses included more than 5000 pregnant women who used metronidazole during pregnancy. Many studies included first trimester exposures. In 1 study, an increased risk of cleft lip (with or without cleft palate) was seen in infants exposed to metronidazole in utero; however, findings were not confirmed. More than 10 randomized placebo-controlled clinical studies enrolled more than 5000 pregnant women to assess use of antibiotics (including metronidazole) for bacterial vaginosis on rate of preterm delivery. Most studies did not show increased risk for congenital anomalies or other adverse fetal outcomes after metronidazole exposure during pregnancy. Increased risk of infant cancer after metronidazole exposure during pregnancy was not found in 3 studies conducted to assess this risk; however, limited ability to detect such a signal. The CDC recommends use of metronidazole for vaginal trichomoniasis during any stage of pregnancy. Multiple studies and meta-analyses have not established an association between metronidazole use during pregnancy and teratogenic or mutagenic effects in infants. 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.

FDA pregnancy category: B Use of metronidazole for trichomoniasis is contraindicated during the first trimester; the manufacturer makes no further recommendations regarding use during pregnancy.

See references

Metronidazole Breastfeeding Warnings

Metronidazole is present in human milk at levels similar to maternal serum levels, and infant serum levels can be similar to infant therapeutic levels. Due to the potential for tumorigenicity shown for metronidazole in mouse and rat studies, discontinuation of the drug or nursing is recommended. Alternatively, nursing mothers may pump and discard their milk during and for 24 hours after metronidazole therapy and feed their infants stored human milk or formula.

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 Excreted into animal milk: Data not available

See references

References for pregnancy information

  1. Morales WJ, Schorr S, Albritton J "Effect of metronidazole in patients with preterm birth in preceding pregnancy and bacterial vaginosis: a placebo-controlled, double-blind study." Am J Obstet Gynecol 171 (1994): 345-9
  2. Mcdonald HM, Oloughlin JA, Vigneswaran R, Jolley PT, Mcdonald PJ "Bacterial vaginosis in pregnancy and efficacy of short-course oral metronidazole treatment: a randomized controlled trial." Obstet Gynecol 84 (1994): 343-8
  3. Sorensen HT, Larsen H, Jensen ES, Thulstrup AM, Schonheyder HC, Nielsen GL, Czeizel A "Safety of metronidazole during pregnancy: a cohort study of risk of congenital abnormalities, preterm delivery and low birth weight in 124 women." J Antimicrob Chemother 44 (1999): 854-5
  4. Thapa PB, Whitlock JA, Worrell KGB, Gideon P, Mitchel EF, Roberson P, Pais R, Ray WA "Prenatal exposure to metronidazole and risk of childhood cancer: A retrospective cohort study of children younger than 5 years." Cancer 83 (1998): 1461-8
  5. "Product Information. Flagyl (metronidazole)." Searle, Skokie, IL.
  6. CDC. Centers for Disease Control and Prevention "Sexually transmitted diseases treatment guidelines, 2010. Available from: URL:" ([2010 Dec 17]):
  7. Donders GGG "Treatment of sexually transmitted bacterial diseases in pregnant women." Drugs 59 (2000): 477-85
  8. Carvajal A, Sanchez A, Hurtarte G "Metronidazole during pregnancy." Int J Gynaecol Obstet 48 (1995): 323-4
  9. Burtin P, Taddio A, Ariburnu O, Einarson TR, Koren G "Safety of metronidazole in pregnancy: a meta-analysis." Am J Obstet Gynecol 172 (1995): 525-9

References for breastfeeding information

  1. "Product Information. Flagyl (metronidazole)." Searle, Skokie, IL.
  2. Moore B, Collier J "Drugs and breast feeding." Br Med J 2 (1979): 211
  3. Erickson SH, Oppenheim GL, Smith GH "Metronidazole in breast milk." Obstet Gynecol 57 (1981): 48-50
  4. Passmore CM, McElnay JC, Rainey EA, D'Arcy PF "Metronidazole excretion in human milk and its effect on the suckling infant." Br J Clin Pharmacol 26 (1988): 45-51
  5. Heisterberg L, Branebjerg PE "Blood and milk concentrations of metronidazole in mothers and infants." J Perinat Med 11 (1983): 114-20
  6. Roberts RJ, Blumer JL, Gorman RL, et al "American Academy of Pediatrics Committee on Drugs: Transfer of drugs and other chemicals into human milk." Pediatrics 84 (1989): 924-36
  7. Gray MS, Kane PO, Squires S "Further observations on metronidazole (flagyl)." Br J Vener Dis 37 (1961): 278-9
  8. Clements CJ "Metronidazole and breast feeding." N Z Med J 92 (1980): 329

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