A randomized sequential allocation study to determine the minimum effective analgesic concentration of levobupivacaine and ropivacaine in patients receiving epidural analgesia for labor.

BACKGROUND: This study was designed to determine and compare the minimum local analgesic concentrations of levobupivacaine and ropivacaine when used in epidural obstetric analgesia.

METHODS: In a double-blind study, healthy women requiring epidural analgesia for labor pain were randomized to receive either ropivacaine or levobupivacaine. Drugs were administered as a 20-ml epidural bolus. The concentration of each started at 0.11% and increased or decreased at intervals of 0.01%, depending on the response of the previous patient, using the technique of up-down sequential allocation. Minimum local analgesic concentrations were calculated using the formula of Dixon and Massey. Efficacy was assessed using visual analog pain scores and motor and sensory block assessments, and safety was assessed by recording maternal and fetal/neonate vital signs and adverse events.

RESULTS: Forty-seven patients received levobupivacaine, and 47 received ropivacaine. Minimum local analgesic concentrations for levobupivacaine (0.077%; 95% CI, 0.058-0.096%) were lower than those for ropivacaine (0.092%; 95% CI, 0.082-0.102%). The 0.015% difference was not statistically significant. There was no notable difference between treatment groups in the proportion of patients reporting drug-related adverse events.

CONCLUSIONS: Levobupivacaine was 19% more potent than ropivacaine and provided similar safety results.