Transfer of lorazepam and its conjugate across the human placenta.

The concentrations of lorazepam and its conjugate were determined in maternal venous serum, in umbilical vein and artery serum, and in amniotic fluid after a single 2 mg intramuscular and 2.5 mg oral maternal administration. During normal delivery (2 mg intramuscular injection) and caesarean section (2.5 mg orally) both the unconjugated and conjugated forms of lorazepam were found in the umbilical circulation and amniotic fluid. The serum protein unbound fraction was 14.0 +/- 4.8 (S.D.) % in maternal circulation and 20.8 +/- 3.1% in umbilical circulation. Generally, lorazepam was a useful anxiolytic agent during normal delivery and as a sedative on the night before caesarean section.