THE PLACENTAL TRANSMISSION OF PETHIDINE

Abstract

Pethidine given intravenously to a pregnant patient began to reach the foetus in measurable quantities within 2 minutes. The level of concentration in cord blood fell exponentially, parallel to, but always lower than, the level in maternal blood. Non-pregnant patients excreted pethidine (in urine) mainly as the demethylated compound, norpethidine; pregnant patients and neonates preferentially excreted pethidine in the unchanged state. Two neonates excreted, respectively, 25 per cent and 40 per cent of a received dose of pethidine in 48 hours. Significantly more pethidine reached the foetus after intravenous than after intramuscular injection. Following intramuscular administration of pethidine to a pregnant patient at term, slightly less than 1 per cent of the dose reached the foetus during the subsequent few hours.