[Acute toxicity of local anesthetics as a function of the patient's condition]

A patient's condition may alter the pharmacokinetic and pharmacodynamic characteristics of local anaesthetics and so increase the risk of toxicity. In the elderly patient, the elimination half-life is increased for both lidocaine and bupivacaine; the risk of overdose is therefore increased when the local anaesthetic agent is given in repeated doses and as a continuous infusion. Cardiotoxicity due to bupivacaine seems to be worsened by pregnancy. In the foetus and newborn, local anaesthetic toxicity gives the same clinical picture as in the adult and is increased in the presence of acidosis and anoxia. Bupivacaine depressive effects are increased by tachycardias, intraventricular blocks and all the conditions which are known to depolarize the cardiac cell membrane (e.g. hyperkaliemia, acidosis, severe hypoxia, myocardial ischaemia). Drug interactions may also potentiate the toxicity of lidocaine and bupivacaine, such as calcium blockers and diazepam. The effects of other conditions (cirrhosis, renal failure, epilepsy) and other drug interactions, specially those modifying free fraction and elimination of local anaesthetics, are also discussed.