Effects of Low Doses of Meperidine on Neonatal Behavior

After meperidine administration during labor, meperidine reaches its highest level in fetal tissues within 2–3 hr. The highest levels of normeperidine, the active metabolite of meperidine, are, on the other hand, determined in fetal tissues by the time between administration of meperidine to the mother and delivery: the greater the drug-to-delivery interval (DDI), the higher the fetal levels of normeperidine. Because of the different times to peak fetal levels of meperidine and normeperidine, it may be possible to partially separate the effects of meperidine and its metabolite on the neonate using the DDI. The purpose of this study was to determine whether low doses of meperidine affected performance on the Brazelton Neonatal Behavioral Assessment Scale (BNBAS), and whether this performance is related to the DDI or to levels of meperidine or to normeperidine. Sixteen control neonates whose mothers received no meperidine and 41 study infants whose mothers received 25–100 mg meperidine intravenously (mean 39 ± 19 mg) were studied. Comparisons of BNBAS scores of control and study infants measured at < 12 hr, again at 3 days of age, and the effect of DDI were made using repeated measures analyses of variance (ANOVA). Correlation techniques were used to examine relationships between BNBAS performance and clinical and pharmacological variables related to drug administration. The BNBAS cluster scores representing regulation of state and number of abnormal reflexes were significantly different in study neonates from control neonates. Performance depended upon test day. Further analysis showed that longer DDIs resulted in less optimal BNBAS performance. The number of abnormal reflexes was significantly related to the DDI at both test times. Longer DDIs resulted in more abnormal reflexes. Cord venous pH and maternal parity were significant covariates. These results suggest that even low doses of meperidine may influence neonatal behavior. Furthermore, the difference in BNBAS scores suggests that less optimal performance with longer DDIs may be caused by normeperidine.