• Anesthesia and analgesia · Nov 2003

    Randomized Controlled Trial Comparative Study Clinical Trial

    The relative motor blocking potencies of bupivacaine and levobupivacaine in labor.

    • Héctor J Lacassie and Malachy O Columb.
    • Anesthesiology Department, Pontificia Universidad Católica de Chile, Santiago, Chile. lacassie@med.puc.cl
    • Anesth. Analg. 2003 Nov 1;97(5):1509-13.

    UnlabelledMinimum local analgesic concentrations (MLAC) have been used to determine the epidural analgesic potencies of bupivacaine and its levo- counterpart. There are no reports of the motor blocking potencies of these drugs. In this study we sought to determine the motor block MLAC of both drugs and determine the relative potency ratio. Sixty ASA physical status I-II parturients were randomized. The first woman in each group received 0.25% wt/vol. Up-down sequential allocation was used to determine subsequent concentrations at a testing interval of 0.025% wt/vol. Effective motor block was defined as a Bromage score <4 within 30 min. The up-down sequences were analyzed with the Dixon and Massey method and probit regression. Two-sided P < 0.05 defined significance. The motor block MLAC for bupivacaine was 0.27% wt/vol (95% confidence interval [CI], 0.25-0.30) and for levobupivacaine was 0.31% wt/vol (95% CI, 0.29-0.34) (P = 0.024), with a levobupivacaine/bupivacaine potency ratio of 0.87 (95% CI, 0.77-0.98). This is the first study to estimate the motor-blocking potency ratio of bupivacaine and levobupivacaine in labor. This study demonstrates that the S-enantiomer of bupivacaine is less potent at motor block than the racemate.ImplicationsWe estimated the motor-blocking potency ratio of bupivacaine and levobupivacaine in labor and demonstrated that the S-enantiomer of bupivacaine is less potent at motor block than the racemate.

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