A comparison of the placental transfer of ropivacaine versus bupivacaine

This study compares the placental transfer of ropivacaine and bupivacaine u sing the dual perfused, single cotyledon human placental model. We studied the effects of maternal/fetal protein binding, maternal ropivacaine concent ration, and fetal pH on ropivacaine transfer. At a clinically relevant mate rnal concentration (1 mu g/mL), the calculated transfer ratios (local anest hetic percent transfer/antipyrine percent transfer) of ropivacaine (0.82 +/ - 0.03) and bupivacaine (0.74 +/- 0.01) were comparable at the completion o f the perfusion experiment (120 min). When the perfusates were modified to simulate actual in vivo plasma protein binding values, the maternal-to-feta l 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%, r espectively. 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 decre ased. This investigation shows that ropivacaine and bupivacaine cross the h uman placenta at a similar rate, despite their differences in lipophilicity and stereochemistry. Placental transfer of both compounds is highly influe nced by maternal and fetal protein concentration and the fetal pH. Implicat ions: The placental transfer of ropivacaine was shown to be similar to that of bupivacaine, and is thus highly influenced by the degree of maternal an d fetal protein binding and fetal pH.