Safety and efficacy of antiemetics used to treat nausea and vomiting in pregnancy.

The safety and efficacy of antiemetic drugs used in the treatment of nausea and vomiting during pregnancy are reviewed. Confirmation of the teratogenicity of drugs in humans is difficult; the risk can be estimated from results of cohort studies and case-control studies. The possible teratogenicity of Bendectin (doxylamine succinate and pyridoxine hydrochloride) was studied thoroughly; although the risk was minimal, the drug was withdrawn from the U.S. market. Whether phenothiazines are teratogenic has still not been conclusively determined. A large number of epidemiological studies have not shown meclizine to be teratogenic in humans. More information about metoclopramide is necessary before it can be safely recommended for use during pregnancy. The risks of using dimenhydrinate and diphenhydramine appear to be low. Pyridoxine is considered safe for use during pregnancy, but its efficacy in treating nausea and vomiting has not been determined. The relative efficacy of these agents has not been determined. The available data suggest that meclizine and dimenhydrinate are the antiemetics that present the lowest risk of teratogenicity; meclizine is the drug of first choice. Phenothiazines should be reserved for treating persistent vomiting that threatens the maternal nutritional status.