Studies on the duration of local anaesthesia: structure/activity relationships in a series of homologous local anaesthetics.

When the number of carbon atoms on the piperidine-nitrogen of the mepivacaine molecule was increased up to four or five carbons, the toxicity of the compounds and the duration of their local anaesthetic effects were increased. With longer N-alkyl-chains, the general toxicity and the local anaesthetic potency - but not the tissue toxicity - were reduced. In dental infiltration anaesthesia only the short-chain compounds offered an acceptable local anaesthesia. In these tests, the medium-chain compounds had a very unfavourable quotient between dental anaesthesia and soft tissue anaesthesia, while the long-chain compounds could not be tested at all in man because of their tissue irritating properties.