Placental Transfer and Pharmacokinetics of Atropine after a Single Maternal Intravenous and Intramuscular Administration

The placental transfer and pharmacokinetics of atropine were studied in 44 healthy parturients undergoing caesarean section. The concentrations in the plasma were determined by a new radioimmunoassay after intravenous (n = 32) or after intramuscular (n = 12) administration of 0.01 mg/kg of atropine. A fast placental transfer with apparent foetal uptake of the drug was found after intravenous injection. There was also a difference in the umbilical vein and artery concentrations after intramuscular administration. The maternal pharmacokinetics of i.v. atropine obeyed a two-compartment open model with a fast distribution phase (mean tα_1/2 = 1.02 min) and quite fast elimination (t_1/2 = 2.56 h). The total apparent volume of distribution was 1.0 1/kg and the total plasma clearance 6.36 ml/min/kg. The mean peak maternal plasma levels after i.m. atropine administration were found at 1.59 h and the mean calculated half-life of elimination was then 2.1 h. No atropine was found in the amniotic fluid.