Pharmacokinetics of 0.2% ropivacaine and 0.2% bupivacaine following caudalblocks in children

Background: Ropivacaine is the first S-enantiomer aminoamide local anaesthe tic in clinical use, and has been found to be less toxic than bupivacaine. Caudal ropivacine has been shown to cause less motor blockade and longer du ration of analgesia in the postoperative period than bupivacaine in childre n. Plasma levels of ropivacaine and bupivacaine have not been previously co mpared in children. This study was undertaken to compare the total venous p lasma concentrations of similar doses of ropivacaine and bupivacaine follow ing caudal administration. Methods: Blood samples were obtained to determine the total venous plasma l evels of the used local anaesthetic in 30 children, aged 2.3-8.7 years, BSA I, given 1 ml . kg(-1) of either 0.2% ropivacaine or 0.2% bupivacaine in a prospective, randomised manner. Results: There were no differences in the individual peak plasma concentrat ions achieved. Time to the measured peak plasma concentration was significa ntly shorter in the bupivacaine group. The plasma concentrations of bupivac aine were significantly lower than for ropivacaine at 60, 90 and 120 min af ter the block. Conclusion: Absorption and tissue distribution of ropivacaine is slower tha n for bupivacaine following caudal administration in children.