Meperidine and normeperidine levels following meperidine administration during labor. II. Fetus and neonate.

The time interval between the administration of meperidine to laboring patients and delivery may affect neonatal status, but sophisticated analytic techniques have not been used to determine the exposure of the fetus to meperidine at various drug-delivery intervals. By means of gas chromatography and mass spectrometry, the concentrations of meperidine and normeperidine (the principle metabolite of meperidine) were quantitated in the umbilical cord venous and arterial plasma at delivery and in the urine of the neonate for three days postpartum. Following 50 mg. of meperidine administered intravenously during labor, fetal exposure to meperidine was highest two to three hours after maternal medication while fetal exposure to normeperidine was highest four hours or more after medication. We conclude from this study that there is a definite but nonlinear relationship between the drug-delivery interval and the amount of meperidine and normeperidine an infant receives; and that the drug-delivery intervals resulting in maximum fetal exposure reported here correspond with those resulting in maximum neonatal depression reported by others.