Placental transfer of metronidazole in the first trimester of pregnancy.

Concentrations of metronidazole and its hydroxy metabolite (I) were determined by a specific chromatographic method in blood, placenta and fetus from 10 women receiving oral metronidazole prior to legal first trimester abortion. In one woman given 2 g of metronidazole 9 hours before abortion, placenta and plasma levels were 6.6 micrograms/g and 13.4 micrograms/ml, respectively. The corresponding values for the hydroxy metabolite (I) were 1.8 micrograms/g and 5.6 micrograms/ml. In nine women receiving 400 mg metronidazole 1 hour before abortion, concentrations of metronidazole in plasma ranged from less than 0.1 to 9.4 micrograms/ml, in placenta from less than 0.1 to 6.3 micrograms/g, and in a fetal tissue from 1.9 to 3.0 micrograms/g. The concentrations of hydroxy metabolite (I) in plasma and placenta and fetal tissue all ranged below those of metronidazole.