Unwanted effects and pharmacokinetics of local anaesthetics (LAs)

LAs are either esters or amides. Esters are rapidly hydrolysed by plasma cholinesterase, and amides are metabolised in the liver. Plasma half-lives are generally short, about 1-2 hours.
Unwanted effects result mainly from escape of LAs into systemic circulation.
Main unwanted effects are:
CNS effects, agitation, confusion, tremors progressing to convulsions and respiratory depression
cardiovascular effects, namely myocardial depression and vasodilatation, leading to fall in blood pressure
occasional hypersensitivity reactions.
LAs vary in the rapidity with which they penetrate tissues, and in their duration of action. Lidocaine penetrates tissues readily and is suitable for surface application; bupivacaine has a particularly long duration of action.