Pharmacokinetics of the placental transfer and distribution of clorazepate and its metabolite nordiazepam in the feto-placental unit and in the neonate.

Clorazepate 20 mg was given i.m. to 49 mothers during the first stage of labour. The elimination of the drug was studied in 27 newborns produced by these mothers. The same dose was given to 13 women who underwent amniocentesis and to 7 women who were breast-feeding. "Total nordiazepam", i.e. the sum of clorazepate and its metabolite nordiazepam, was determined by gas-liquid chromatography in maternal blood, umbilical cord blood (both arterial and venous), amniotic fluid and in milk. Clorazepate was found to cross the placental barrier slowly, but nordiazepam was transferred more rapidly. Nordiazepam was found in the milk and in the blood of neonates after breast-feeding had started.