A comparison of the placental transfer of ropivacaine versus bupivacaine.

UNLABELLED: This study compares the placental transfer of ropivacaine and bupivacaine using the dual perfused, single cotyledon human placental model. We studied the effects of maternal/fetal protein binding, maternal ropivacaine concentration, and fetal pH on ropivacaine transfer. At a clinically relevant maternal concentration (1 microg/mL), the calculated transfer ratios (local anesthetic percent transfer/antipyrine percent transfer) of ropivacaine (0.82 +/- 0.03) and bupivacaine (0.74 +/- 0.01) were comparable at the completion of the perfusion experiment (120 min). When the perfusates were modified to simulate actual in vivo plasma protein binding values, the maternal-to-fetal transfer of ropivacaine and bupivacaine decreased significantly (P < 0.05) as indicated by transfer ratios of 0.42% +/- 0.07% and 0.40% +/- 0.03%, respectively. No saturation of the transfer process was observed for either drug at the maternal concentrations investigated. The placental transfer of both local anesthetic agents increased significantly as the fetal pH decreased. This investigation shows that ropivacaine and bupivacaine cross the human placenta at a similar rate, despite their differences in lipophilicity and stereochemistry. Placental transfer of both compounds is highly influenced by maternal and fetal protein concentration and the fetal pH. IMPLICATIONS: The placental transfer of ropivacaine was shown to be similar to that of bupivacaine, and is thus highly influenced by the degree of maternal and fetal protein binding and fetal pH.