Metronidazole

The Basics

What is Metronidazole?

Used to treat infections of the reproductive system, gastrointestinal (GI) tract, skin, heart, bone, joint, lung, blood, nervous system, and other areas of the body.

Brand names for Metronidazole

Metronidazole Injection

How Metronidazole is classified

Anti-Infective Agents, Antibacterial Agents, Antiprotozoal Agents, Nitroimidazoles

Metronidazole During Pregnancy

Metronidazole pregnancy category

Category BNote that the FDA has deprecated the use of pregnancy categories, so for some medications, this information isn’t available. We still think it’s useful to list historical info, however, given what a common proxy this has been in the past.

What we know about taking Metronidazole while pregnant

Metronidazole crosses the placental barrier and enters the fetal circulation rapidly. Reproduction studies have been performed in rats at doses up to five times the human dose and have revealed no evidence of impaired fertility or harm to the fetus due to metronidazole. Metronidazole administered intraperitoneally to pregnant mice at approximately the human dose caused fetotoxicity; administered orally to pregnant mice, no fetotoxicity was observed. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, and because metronidazole is a carcinogen in rodents, these drugs should be used during pregnancy only if clearly needed.

Taking Metronidazole While Breastfeeding

What are recommendations for lactation if you're taking Metronidazole?

With maternal intravenous and oral therapy, breastfed infants receive metronidazole in doses that are less than those used to treat infections in infants, although the active metabolite adds to the total infant exposure. Plasma levels of the drug and metabolite are measurable, but less than maternal plasma levels. Case reports of candidal infections and diarrhea have been reported, and a comparative trial suggested that oral and rectal colonization with Candida might be more common in infants exposed to metronidazole. Neither topical nor vaginal metronidazole have been studied during breastfeeding. After vaginal administration, plasma levels are less than 2% of those after a 500 mg oral dose. After topical administration, blood levels are about 1% of the peak plasma levels after a 250 mg oral dose. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.[1] Because of the well demonstrated genotoxicity and mutagenicity in bacteria, carcinogenicity in animals, and possible mutagenicity in humans,[2][3] concern has been raised about exposure of healthy infants to metronidazole via breastmilk.[4] The relevance of these findings has been questioned and no definitive study has yet been performed in humans.[3][5] Opinions vary among experts on the advisability of using metronidazole during longer-term therapy while breastfeeding, but some sources recommend discontinuing breastfeeding for 12 to 24 hours after single-dose maternal treatment.[4][6] Other drugs are available for some conditions that metronidazole is used to treat. Topical or vaginal use of metronidazole during breastfeeding is unlikely to be of concern, although the manufacturer of one vaginal product recommends not breastfeeding during treatment and for 2 days after the last dose.

Maternal / infant drug levels

With maternal intravenous and oral therapy, breastfed infants receive metronidazole in doses that are less than those used to treat infections in infants, although the active metabolite adds to the total infant exposure. Plasma levels of the drug and metabolite are measurable, but less than maternal plasma levels. Case reports of candidal infections and diarrhea have been reported, and a comparative trial suggested that oral and rectal colonization with Candida might be more common in infants exposed to metronidazole. Neither topical nor vaginal metronidazole have been studied during breastfeeding. After vaginal administration, plasma levels are less than 2% of those after a 500 mg oral dose. After topical administration, blood levels are about 1% of the peak plasma levels after a 250 mg oral dose. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.[1] Because of the well demonstrated genotoxicity and mutagenicity in bacteria, carcinogenicity in animals, and possible mutagenicity in humans,[2][3] concern has been raised about exposure of healthy infants to metronidazole via breastmilk.[4] The relevance of these findings has been questioned and no definitive study has yet been performed in humans.[3][5] Opinions vary among experts on the advisability of using metronidazole during longer-term therapy while breastfeeding, but some sources recommend discontinuing breastfeeding for 12 to 24 hours after single-dose maternal treatment.[4][6] Other drugs are available for some conditions that metronidazole is used to treat. Topical or vaginal use of metronidazole during breastfeeding is unlikely to be of concern, although the manufacturer of one vaginal product recommends not breastfeeding during treatment and for 2 days after the last dose.

Possible effects of Metronidazole on milk supply

Relevant published information was not found as of the revision date.

Possible alternatives to Metronidazole

(Anaerobic bacterial infections) Amoxicillin and Clavulanic Acid, Clindamycin, Doxycycline; (Giardiasis) Tinidazole; (Topical for Rosacea) Azelaic Acid; (Vaginal) Clindamycin.