Metronidazole and alcohol in pregnancy

To the Editor.— Concerning the recent question about the safety of metronidazole use in pregnancy, 1 I would like to add a note of caution based on our experimental data. As correctly pointed out by Dr Friedrich, who answered the letter to JAMA , there are no reports on the teratogenicity of metronidazole in humans. For all practical purposes metronidazole is not teratogenic in experimental animals, 2 unless administered in extremely high doses. However, if metronidazole together with ethyl alcohol is given to pregnant mice, fetotoxicity and teratogenicity occur far in excess of that noted in animals exposed to each of these drugs administered separately. 2 It seems that, in mice, metronidazole potentiates the teratogenicity of alcohol. Since metronidazole may cause intolerance to alcohol 3 as well as dizziness and nausea if taken together with alcohol, a warning against the simultaneous use of two drugs in pregnancy may be warranted.