Pregnancy: Pregnancy Category: B.
Metronidazole crosses the placental barrier and enters the fetal circulation rapidly. There are 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.
Lactation: Because of the potential for tumorigenicity shown for metronidazole in mouse and rat studies, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. Metronidazole is secreted in breastmilk in concentrations similar to those found in plasma.