Naguib M. Magboul MM. Samarkandi AH. Attia M., Adverse effects and drug interactions associated with local and regional anaesthesia. Drug Safety. 18(4):221-50, 1998.
Systemic and localized adverse effects of local anesthetic drugs usually occur because of excessive dosage, rapid absorption or inadvertent intravascular injection. Small children are more prone than adults to methemoglobinemia, and the combination of sulfonamides and prilocaine, even when correctly administered, should be avoided in this age group. The incidence of true allergy to local anesthetics is rare. All local anesthetics can cause CNS toxicity and cardiovascular toxicity if accidental intravenous injection or an absolute overdose increases their plasma concentrations. Excitation of the CNS may be manifested by numbness of the tongue and perioral area, and restlessness, which may progress to seizures, respiratory failure and coma. Bupivacaine is the local anesthetic most frequently associated with seizures. Treatment of CNS toxicity includes maintaining adequate ventilation and oxygenation, and controlling seizures with the administration of thiopental sodium or benzodiazepines. Cardiovascular toxicity generally begins after signs of CNS toxicity have occurred. Bupivacaine and etidocaine appear to be more cardiotoxic than most other commonly used local anesthetics. Sudden onset of profound bradycardia and asystole during neuraxial blockade is of great concern and the mechanism(s) remains largely unknown. Treatment of cardiovascular toxicity depends on the severity of effects. Cardiac arrest caused by local anesthetics should be treated with cardiopulmonary resuscitation procedures, but bupivacaine-induced dysrhythmias may be refractory to treatment. Many recent reports of permanent neurological complications involved patients who had received continuous spinal anesthesia through a microcatheter. Injection of local anesthetic through microcatheters and possibly small-gauge spinal needles results in poor CSF mixing and accumulation of high concentrations of local anesthetic in the areas of the lumbosacral nerve roots. In contrast to bupivacaine, the hyperbaric lidocaine (lignocaine) formulation carries a substantial risk of neurotoxicity when given intrathecally. Drugs altering plasma cholinesterase activity have the potential to decrease hydrolysis of ester-type local anesthetics. Drugs inhibiting hepatic microsomal enzymes, such as cimetidine, may allow the accumulation of unexpectedly high (possibly toxic) blood concentrations of lidocaine. Reduction of hepatic blood flow by drugs or hypotension will decrease the hepatic clearance of amide local anesthetics. Special caution must be exercised in patients taking digoxin, calcium antagonists and/or beta-blockers.