Relative analgesic potencies of levobupivacaine and ropivacaine for caudal anesthesia in children

BACKGROUND: Comparing relative potency of new local anesthetics, such as levobupivacaine and ropivacaine, by the minimum local analgesic concentration model has not been described for caudal anesthesia. Therefore, we performed a prospective, randomized, double-blind study to determine the minimum local analgesic concentrations of a caudal single shot of ropivacaine and levobupivacaine in children and to describe the upper dose-response curve. METHODS: We performed a two-stage prospective, randomized, double-blind study comparing the dose-response curves of caudal ropivacaine and levobupivacaine in children. In phase 1, 80 boys were randomized to receive either ropivacaine or levobupivacaine. In the second phase a further 32 patients were randomly allocated to receive caudal anesthesia with doses designed to delineate the upper doseresponse range (the 50% effective dose [ED ₅₀]-ED ₉₅ range). RESULTS: There were no significant differences in ED ₅₀ values for caudal ropivacaine and levobupivacaine. The ED50 for levobupivacaine estimated from the Dixon Massey method was 0.069% (95% CI 0.056%-0.082%) and for ropivacaine was 0.075% (95% CI 0.058%-0.092%). Estimated by isotonic regression the ED ₅₀ and ED95 respectively of levobupivacaine were 0.068 (0.04-0.09) and 0.20% (95% CI 0.16%-0.24%). For ropivacaine ED ₅₀ and ED ₉₅ were 0.066 (0.033- 0.098) and 0.225% (95% CI 0.21%-0.24%). CONCLUSIONS: In children receiving one minimum alveolar anesthetic concentration of sevoflurane, there were no significant differences in the ED ₅₀ for caudal levobupivacaine and ropivacaine. The potency ratio at ED ₅₀ was 0.92 and 0.89 at ED ₉₅, indicating that caudal levobupivacaine and ropivacaine have a similar potency.