A study of the plasma concentrations of lorazepam in mother and neonate.

A standard dose of lorazepam 2.5 mg was given i.v. to two groups of mothers: (a) before surgical induction of labour and (b) at the beginning of the second stage of labour. A group of non-pregnant women was studied as control. Plasma concentrations of lorazepam were measured by gas-liquid chromatography, in the mothers before delivery, and in the mother and neonate at delivery and 24 and 48 h thereafter. Concentrations at delivery in the neonates were similar to those in the mothers in group (a), but significantly less in group (b). Fetal concentration rarely exceeded that in the mother. Measurements after delivery indicated that the neonates were able to metabolize lorazepam at the same rate as the mothers. Of the 22 neonates studied only one had an Apgar score of less than 8 at 5 min and this score was 10 at 10 min.