A review of the metabolism of amide local anaesthetic agents.

(1) Amide local anaesthetics are almost completely metabolized before excretion in both animals and man. (2) Considerable interspecies variability occurs in the quantitative excretion of local anaesthetic metabolites; however, qualitative similarities often exist. (3) The secondary amine metabolite of lignocaine, MEGX, is capable of reacting in vivo with acetaldehyde, formed as a metabolite of ethyl alcohol, to produce a cyclic condensation product. (4) Although hydrolysis in man of the secondary amine metabolite of lignocaine, MEGX, appears extensive, the same is not true for the metabolic analogue produced from mepivacaine, PPX. (5) Metabolism of mepivacaine by the neonate is impaired, but the excretion process in the newborn is capable of eliminating the drug within 24 hr after birth. (6) Metabolic data on bupivacaine and etidocaine are incomplete. The latter compound appears to have a more rapid plasma clearance.