Mechanism of action of local anaesthetic agents and biotoxins.

Four current theories for the mechanism of action of local anaesthetics are that these drugs: (1) interfere with some chemical, such as acetylcholine, that is involved in nervous conduction; (2) alter the density of fixed charges on the surface of the membrane; (3) cause an expansion of some volume of membrane that is critical for conduction; and (4) react with some specific receptor in the nerve membrane. The first theory fails for lack of evidence that acetylcholine is involved physiologically in conduction. The other three theories, however, all seem to apply.