General Information


  • Metronidazole crosses the placenta. Studies have not shown an increased risk of congenital anomalies or other adverse events to the fetus following maternal use during pregnancy
  • Because metronidazole was carcinogenic in some animal species, concern has been raised whether metronidazole should be used during pregnancy, however, available studies have not shown an increased risk of cancer following human exposure or infant cancer following metronidazole exposure during pregnancy
  • Metronidazole is considered compatible during pregnancy


  • The relative infant dose (RID) of metronidazole has been reported as high as 24%
  • Both metronidazole and its active metabolite are detectable in infant serum after exposure via breastmilk, however, exposure via breasmilk is significantly lower compared to neonates that are given therapeutic doses of metronidazole
  • There are some case reports of infant diarrhea via breastmilk exposure
  • Metronidazole is considered compatible with breastfeeding and holding breastfeeding following metronidazole doses (including the 2 g dose) is not necessary

Monitor the infant for signs of gastrointestinal intolerance.

Suspected or confirmed anaerobic infections including intra-abdominal, biliary, central nervous system, Clostridium difficile, Giardia and pelvic infections.

Also used in Crohns disease, bacterial vaginosis, trichomoniasis, and hepatic encephalopathy

Used in combination therapy with a beta-lactam for chorioamniotitis and endometritis.

With prolonged therapy (> 6 wks) or if symptoms develop assess for peripheral/optic neuropathy

  • GI symptoms common - especially nausea/vomiting and metallic taste
  • Peripheral/optic neuropathy with extended therapy
  • Disulfiram-like reaction with alcohol (severe vomiting)
  • Rare neurotoxicity including aseptic meningitis and encephalopathy
  • Luekopenia, neutropenia

Ethanol - disulfiram like reaction

Increases levels of cyclosporine, lithium, warfarin, and phenobarbital and phenytoin

Antimicrobial class: Nitroimidazole