[Clinical and toxicologic study of axillary plexus block with prilocaine or mepivacaine]

A prospective controlled double-blind study was designed to compare the efficacy and the toxicity of mepivacaine and prilocaine for the axillary blockade of the brachial plexus. Twenty patients in each group received 40 ml of either 1.5% mepivacaine or 1.5% prilocaine. The sensory and the motor blockade achieved in both groups were comparable. The mean plasma levels attained following mepivacaine were significantly higher than those attained after prilocaine (peak-plasma level (mean +/- SD): 2.02 +/- 0.28 micrograms/ml vs 5.37 +/- 1.83 micrograms/ml). In four patients of the mepivacaine group, the plasma levels entered the toxic range. While no methemoglobinemia could be detected following mepivacaine, four of the patients receiving prilocaine developed methemoglobinemia with a maximum level of 10%. No complications due to methemoglobinemia were observed in any of the patients. Because of its significantly lower toxic potential, prilocaine seems to be the better local anaesthetic for axillary blockade of the brachial plexus.