MATERNAL, FETAL AND PLACENTAL DISTRIBUTION OF LIDOCAINE-EPINEPHRINE AND BUPIVACAINE AFTER EPIDURAL ADMINISTRATION FOR CESAREAN-SECTION

Bupivacaine and lidocaine are both lipophilic drugs, bupivacaine being more lipophilic and protein-bound. Our earlier studies, using human p lacenta perfused in vitro, showed that increased placental binding of bupivacaine restricts fetal transfer compared to the higher fetal tran sfer of lidocaine. However, placental tissue concentrations of local a nesthetics have not been determined in the clinical context. Term part urients were randomized to receive either 2% lidocaine-epinephrine (n = 10) or 0.5% bupivacaine (n = 10) through a lumbar epidural catheter for elective cesarean section. Total drug concentrations of lidocaine and bupivacaine in maternal and umbilical plasma and placental tissue were determined. There was a higher incidence of maternal hypotension in the lidocaine-epinephrine group than in the bupivacaine group (7/10 vs 1/10, P < 0.05). At delivery, fetal/maternal ratios for total conc entrations of lidocaine and bupivacaine were similar (0.49 vs 0.42. Th e mean placental tissue/maternal plasma concentration ratio of lidocai ne was higher than that of bupivacaine (1.45 vs 1.01, P < 0.05). The m ean amount of the drug retained in the placenta per unit of dose (mg/k g) was also higher in the lidocaine-epinephrine group, although this d ifference did not reach statistical significance (0.46 mg/unit dose vs 0.40 mg/unit dose). Values for area under the concentration-time curv es per unit of dose were similar. In conclusion, maternal plasma conce ntrations, fetal/maternal concentration ratios and placental tissue bi nding of lidocaine resembled those of bupivacaine after epidural admin istration. These findings are probably explainable by the effect of ma ternal hypotension on the distribution of lidocaine.