[Neurotoxicity of dibucaine on the isolated rabbit cervical vagus nerve]

The neurotoxicity of dibucaine was compared with that of commercially available local anesthetics in studies using rabbit desheathed cervical vagus nerve preparation. Dibucaine dose-dependently suppressed the evoked action potential of myelinated A beta nerve component and nonmyelinated C nerve component. The potential of A beta nerve component was more strongly suppressed, compared with that of C nerve component. At low concentrations of 0.0001-0.001%, the suppression was reversible and recovery with C nerve component was faster and more complete. At higher concentrations, the suppression was irreversible. The minimum concentrations of irreversible blockade were 0.003% for A beta nerve component and 0.03% for C nerve component. Electron microscopically, marked damages in the myelin layer and intraaxonal structure were observed in nerves treated with 0.03% dibucaine. When the neurotoxic effect of dibucaine was compared, in terms of safety margins (minimum concentration of irreversible blockade/clinically used concentrations), with those of commercially available local anesthetics, the rank order was dibucaine, tetracaine and bupivacaine; dibucaine showing the lowest safety margin.