Last update: Nov. 3, 2018

C6 H9 N3 O3

Very Low Risk for breastfeeding

Not risky for breastfeeding or infant.

An antiinfective from the imidazole family indicated in the treatment of giardiasis, amebiasis, trichomoniasis and anaerobic infections (bacteroides and clostridium).
Oral administration one to three times a day. Intravenous use in severe cases.
Authorized and widely used in pediatrics. The dose for babies under two months is 15 mg/kg/day and for those older than two months it is 30 mg/kg/day (AEMPS 2018).

There are old studies that showed carcinogenic effects in rats receiving high doses. This has not been demonstrated in humans (Falagas 1998, Fahrig 1997, Beard 1988, Roe 1985), there still being a great deal of controversy (Adil 2018, Friedman 2009) and metronidazole is one of the most used antibiotics in vaginal, intestinal and other infections and whose use in humans is spreading (Adil 2018, Sobel 2015).

It is excreted in breastmilk in moderate but clinically insignificant amounts (Zhang 1997, Passmore 1988, Heisterberg 1983, Erickson 1981, Gray 1961).

No problems have been observed in infants whose mothers were taking it (Passmore 1988, Gray 1961), except for a possible case of diarrhea (Clements 1980). Plasma levels in these infants are undetectable or very low (Passmore 1988, Gray 1961).

Metronidazole can turn body fluids red and give a bitter or metallic taste to milk (Chin 2001, Andersson 1981), without this being detrimental. Although opinions are divided (Huang 2016), being contraindicated for some (van der Woude 2015 and 2010, Nielsen 2014, Yarur 2013), various medical associations, experts and expert consensus consider its use to be safe during breastfeeding ( Hale 2017 p 647, Schulze 2014, Kong 2013, Rowe 2013, Bar-Oz 2003, Einarson 2000, Rubin 1986). When the dose is large, some authors recommend waiting 12 to 24 hours after administration before breastfeeding in order to minimize exposure (Damas 2015, Huang 2014, Rowe 2013, CDC 2010, WHO 2002).

When it comes to mothers of premature or newborn babies, who are unable to metabolize metronidazole well, it may be prudent either to use the minimum effective dose or to seek an alternative.

See below the information of this related product:


Suggestions made at e-lactancia are done by APILAM´s pediatricians and pharmacists, and are based on updated scientific publications.
It is not intended to replace the relationship you have with your doctor but to compound it.

Jose Maria Paricio, Founder & President of APILAM/e-Lactancia

Your contribution is essential for this service to continue to exist. We need the generosity of people like you who believe in the benefits of breastfeeding.

Thank you for helping to protect and promote breastfeeding.

José María Paricio, founder of e-lactancia.

Other names

C6 H9 N3 O3 is Metronidazole in Molecular formula.

Is written in other languages:

C6 H9 N3 O3 is also known as


C6 H9 N3 O3 belongs to these groups or families:


Main tradenames from several countries containing C6 H9 N3 O3 in its composition:


Variable Value Unit
Bioavailability 100 %
Molecular weight 171 daltons
Protein Binding 10 %
pKa 3,09 -
Tmax 1 - 3 hours
T1/2 6 - 8 hours
M/P ratio 0,8 - 1,2 -
Theoretical Dose 0,7 ( 0,17 - 2,3 ) mg/Kg/d
Relative Dose 7 ( 1.7 - 23 ) %
Relat.Ped.Dose 2,3 ( 0,6 - 7,6 ) %


  1. Adil M, Iqbal W, Adnan F, Wazir S, Khan I, Khayam MU, Kamal MA, Ahmad S, Ahmad J, Khan IN. Association of Metronidazole with Cancer: A Potential Risk Factor or Inconsistent Deductions? Curr Drug Metab. 2018 Abstract
  2. AEMPS-Sanofi. Metronidazol. Ficha técnica. 2018 Full text (in our servers)
  3. Huang VW, Chang HJ, Kroeker KI, Goodman KJ, Hegadoren KM, Dieleman LA, Fedorak RN. Management of Inflammatory Bowel Disease during Pregnancy and Breastfeeding Varies Widely: A Need for Further Education. Can J Gastroenterol Hepatol. 2016 Abstract Full text (link to original source) Full text (in our servers)
  4. van der Woude CJ, Ardizzone S, Bengtson MB, Fiorino G, Fraser G, Katsanos K, Kolacek S, Juillerat P, Mulders AG, Pedersen N, Selinger C, Sebastian S, Sturm A, Zelinkova Z, Magro F; European Crohn’s and Colitis Organization. The second European evidenced-based consensus on reproduction and pregnancy in inflammatory bowel disease. J Crohns Colitis. 2015 Abstract Full text (link to original source) Full text (in our servers)
  5. Sobel R, Sobel JD. Metronidazole for the treatment of vaginal infections. Expert Opin Pharmacother. 2015 Abstract
  6. FDA Hospira. Metronidazole.. Drug Summary. 2015 Full text (in our servers)
  7. Damas OM, Deshpande AR, Avalos DJ, Abreu MT. Treating Inflammatory Bowel Disease in Pregnancy: The Issues We Face Today. J Crohns Colitis. 2015 Abstract Full text (in our servers)
  8. Schulze H, Esters P, Dignass A. Review article: the management of Crohn's disease and ulcerative colitis during pregnancy and lactation. Aliment Pharmacol Ther. 2014 Abstract Full text (link to original source) Full text (in our servers)
  9. Huang VW, Habal FM. From conception to delivery: managing the pregnant inflammatory bowel disease patient. World J Gastroenterol. 2014 Abstract Full text (link to original source) Full text (in our servers)
  10. Nielsen OH, Maxwell C, Hendel J. IBD medications during pregnancy and lactation. Nat Rev Gastroenterol Hepatol. 2014 Abstract
  11. Rowe H, Baker T, Hale TW. Maternal medication, drug use, and breastfeeding. Pediatr Clin North Am. 2013 Feb;60(1):275-94. Abstract
  12. Yarur A, Kane SV. Update on pregnancy and breastfeeding in the era of biologics. Dig Liver Dis. 2013 Abstract Full text (link to original source) Full text (in our servers)
  13. Kong YL, Tey HL. Treatment of acne vulgaris during pregnancy and lactation. Drugs. 2013 Abstract
  14. CDC - Workowski KA, Berman S; Centers for Disease Control and Prevention (CDC). Sexually transmitted diseases treatment guidelines, 2010. MMWR Recomm Rep. 2010 Abstract Full text (link to original source) Full text (in our servers)
  15. Friedman GD, Jiang SF, Udaltsova N, Quesenberry CP Jr, Chan J, Habel LA. Epidemiologic evaluation of pharmaceuticals with limited evidence of carcinogenicity. Int J Cancer. 2009 Abstract
  16. Bar-Oz B, Bulkowstein M, Benyamini L, Greenberg R, Soriano I, Zimmerman D, Bortnik O, Berkovitch M. Use of antibiotic and analgesic drugs during lactation. Drug Saf. 2003 Abstract
  17. WHO / UNICEF. BREASTFEEDING AND MATERNAL MEDICATION Recommendations for Drugs in the Eleventh WHO Model List of Essential Drugs. Department of Child and Adolescent Health and Development (WHO/UNICEF) 2002 Full text (link to original source) Full text (in our servers)
  18. Chin KG, McPherson CE 3rd, Hoffman M, Kuchta A, Mactal-Haaf C. Use of anti-infective agents during lactation: Part 2--Aminoglycosides, macrolides, quinolones, sulfonamides, trimethoprim, tetracyclines, chloramphenicol, clindamycin, and metronidazole. J Hum Lact. 2001 Feb;17(1):54-65. Abstract
  19. Einarson A, Ho E, Koren G. Can we use metronidazole during pregnancy and breastfeeding? Putting an end to the controversy. Can Fam Physician. 2000 Abstract Full text (link to original source) Full text (in our servers)
  20. Falagas ME, Walker AM, Jick H, Ruthazer R, Griffith J, Snydman DR. Late incidence of cancer after metronidazole use: a matched metronidazole user/nonuser study. Clin Infect Dis. 1998 Abstract
  21. Zhang Y, Zhang Q, Xu Z. [Tissue and body fluid distribution of antibacterial agents in pregnant and lactating women]. Zhonghua Fu Chan Ke Za Zhi. 1997 Abstract
  22. Fahrig R, Engelke M. Reinvestigation of in vivo genotoxicity studies in man. I. No induction of DNA strand breaks in peripheral lymphocytes after metronidazole therapy. Mutat Res. 1997 Abstract
  23. Passmore CM, McElnay JC, Rainey EA, D'Arcy PF. Metronidazole excretion in human milk and its effect on the suckling neonate. Br J Clin Pharmacol. 1988 Abstract Full text (link to original source) Full text (in our servers)
  24. Beard CM, Noller KL, O'Fallon WM, Kurland LT, Dahlin DC. Cancer after exposure to metronidazole. Mayo Clin Proc. 1988 Abstract
  25. Rubin PC. Prescribing in pregnancy. General principles. Br Med J (Clin Res Ed). 1986 Abstract
  26. Roe FJ. Safety of nitroimidazoles. Scand J Infect Dis Suppl. 1985 Abstract
  27. Heisterberg L, Branebjerg PE. Blood and milk concentrations of metronidazole in mothers and infants. J Perinat Med. 1983 Abstract
  28. Erickson SH, Oppenheim GL, Smith GH. Metronidazole in breast milk. Obstet Gynecol. 1981 Abstract
  29. Andersson KE. Pharmacokinetics of nitroimidazoles. Spectrum of adverse reactions. Scand J Infect Dis Suppl. 1981 Abstract
  30. Clements CJ. Metronidazole and breast feeding. N Z Med J. 1980 Abstract
  31. Wood BA, Monro AM. Pharmacokinetics of tinidazole and metronidazole in women after single large oral doses. Br J Vener Dis. 1975 Abstract Full text (link to original source) Full text (in our servers)
  32. GRAY MS, KANE PO, SQUIRES S. Further observations on metronidazole (Flagyl). Br J Vener Dis. 1961 Abstract Full text (link to original source) Full text (in our servers)

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