DIFFERENTIAL NERVE BLOCKING ACTIVITY OF AMINO-ESTER LOCAL ANAESTHETICS

• Published in: British journal of anaesthesia : BJA Vol. 57; no. 6; pp. 612 - 620
• Main Authors: WILDSMITH, J.A.W., GISSEN, A.J., GREGUS, J., COVINO, B.J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.1985; Oxford University Press
• Subjects: Action Potentials - drug effects; Anesthetics, Local - pharmacology; Anesthetics. Neuromuscular blocking agents; Animals; Autonomic Fibers, Preganglionic - drug effects; Biological and medical sciences; Dose-Response Relationship, Drug; Medical sciences; Nerve Block; Nerve Fibers - drug effects; Nerve Fibers, Myelinated - drug effects; Neural Conduction - drug effects; Neuropharmacology; Pharmacology. Drug treatments; Rabbits; Solubility; Time Factors; Vagus Nerve; Local anesthetic; Vertebrata; Specificity; Mammalia; Aminoester; Animal; Rabbit; Lagomorpha; Mechanism of action; Nerve fiber; In vitro
• ISSN: 0007-0912; 1471-6771
• DOI: 10.1093/bja/57.6.612

The in vitro sensitivities to local anaesthetic blockade of A, B and C nerve fibres in rabbit vagus nerves were examined using a series of structurally similar amino-ester agents which varied in lipid solubility and anaesthetic potency. A fibres were found to be the most sensitive and C fibres the least sensitive to conduction blockade with all the agents, provided that equilibrium blockade was allowed to develop. A correlation existed between the intrinsic anaesthetic potency of the various agents and their lipid solubilities. Equipotent concentrations of the drugs blocked C fibres at approximately the same rate, but there were marked variations in the rate at which A fibres were blocked. Amethocaine, an agent of high lipid solubility, blocked A fibres more quickly than C. As lipid solubility decreased through the series studied, so the onset of conduction blockade of A fibres was prolonged. It is suggested that this related to decreasing ability to penetrate the lipid diffusion barriers around A fibres. The traditional view that C fibres were more sensitive to block may have arisen because of confusion between absolute sensitivity and rate of development of conduction blockade.