Topic overview

Start with the big picture

Local anaesthetics enter the axon mainly in their unionized form, then the ionized form binds intracellular voltage-gated sodium channels. This use-dependent block is more effective in frequently active nerves, helping explain why pain sensation can be lost before touch or motor function. The aromatic ring, intermediate linkage and amine group distinguish ester from amide agents and relate to their metabolism. Onset, potency and duration are influenced by factors including pKa, lipid solubility, protein binding and local tissue conditions. The topic also surveys topical, infiltrative, regional and neuraxial routes, selected adjuncts, and important toxicity concerns. Together, these principles provide a framework for understanding clinical use and safer administration without replacing agent-specific guidance.