Local complications of infusing local anesthetics include bleeding, infection, inflammation, and neuropathy from direct injection of a nerve. Systemic complications can occur from absorption of excessive amounts of infiltrated drug, or accidental intravascular injection. Serious toxicity is due to CNS and cardiovascular effects. CNS effects are due to both central excitatory and depressive action range from mild effects such as tongue numbness, apprehension, and restlessness, to moderate reactions such as as perioral tingling, tremors, slurred speech and drowsiness, to severe effects such as seizures, cardiorespiratory depression, coma and death. Cardiovascular effects include palpitations, hypertension, ventricular dysrhythmia, myocardial depression, bradycardia, hypotension, and cardiovascular collapse.

Treatment for lidocaine and bupivicaine toxicity is generally supportive (Podrid). When toxicity is suspected and the infiltration site was an extremity, a pneumatic tourniquet can be placed to limit venous return of the drug. Hypotension should be treated with IV fluids, Trendelenburg positioning, and vasopressors if needed. Bradyarrhythmias can be treated with atropine. Convulsions are generally responsive to diazapam are lorazepam. A prolonged QRS complex may be reversed by sodium bicarbonate. Hemodialysis, hemoperfusion and multidose activated charcoal are not effective in lidocaine or bupivicane toxicity.

True allergic reactions to local anesthetics are rare. They occur more frequently with esters than amides, and there is no cross reactivity between these groups, so amides may be used for patients with ester sensitivity. The allergic reaction to esters is usually due to a metabolite, para-amino benzoic acid (PABA). Allergic reactions to amides are usually attributable to the preservative methylparaben (MPB) in some commercial preparations.