• Elliot Yung, Joel M Yarmush, Jonathan Weinberg, Joseph J SchianodiCola, and Sidhartha D Ray.
• Department of Anesthesiology, New York Methodist Hospital, Brooklyn, NY 11215, USA.
• Pharmacology. 2009 Jan 1;83(6):356-9.

AimThis study investigates the relative potencies and ED(50) of the local anesthetics lidocaine and chloroprocaine in a sciatic block in Sprague-Dawley rats.MethodsThe study involved 80 rats (chloroprocaine n = 40, lidocaine n = 40). Each rat was injected close to the sciatic nerve with 0.1 ml of the concentration of local anesthetic being tested. Using the up-and-down allocation technique, the next concentration was determined by the response of the previous subject to a higher or lower concentration. A successful block was assessed by pinching the fifth metatarsal. Absent vocalization and a very weak withdrawal response were defined as the onset of block.ResultsUsing the up-and-down methodology, the estimates of ED(50) for chloroprocaine was 0.1 ml of 1.2% (with 95% CI of 1.1-1.6), and that for lidocaine was 0.1 ml of 0.65% (with 95% CI of 0.65-0.88), giving a lidocaine/chloroprocaine potency ratio of 1.85 (with 95% CI of 1.66-2.61).DiscussionUsing the results of this study, the effects of the two drugs can be compared using the commercially available concentrations of chloroprocaine and lidocaine in a peripheral nerve block.Copyright 2009 S. Karger AG, Basel.

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