Transfer in vitro of three benzodiazepines across the human placenta.

A comparative study of the placental transfer to the foetus of three benzodiazepines was performed using a dual perfusion system of the human placental lobule. A transport fraction was calculated for each benzodiazepine and was compared with reference substances. Relative to antipyrine, the transport fraction of diazepam was 85%, and that of nordiazepam was 84%. The transport fraction of clorazepate represented only 20% of that of tritiated water. The relatively high transfer of diazepam and nordiazepam can be attributed to their high lipid solubility, and the lower transfer of clorazepate is due to its polar nature. It is suggested that in certain instances this benzodiazepine may be of especial value to obstetricians.