Adverse Effects

The central nervous and cardiopulmonary systems are most commonly affected by high plasma levels of local anesthetics. Local anesthetics given in initially high doses produce central nervous system (CNS) stimulation characterized by restlessness, disorientation, tremors, and at times clonic convulsions. Continued exposure to high concentrations results in general CNS depression; death occurs from respiratory failure secondary to medullary depression. Treatment requires ventilatory assistance and drugs to control the seizures. The ultra-short-acting barbiturates and the benzodi-azepine derivatives, such as diazepam, are effective in controlling these seizures. Respiratory stimulants are not effective. CNS manifestations generally occur before cardiopulmonary collapse.

Cardiac toxicity is generally the result of drug-induced depression of cardiac conduction (e.g., atrioven-tricular block, intraventricular conduction block) and systemic vasodilation. These effects may progress to severe hypotension and cardiac arrest.

Allergic reactions, such as red and itchy eczematoid dermatitis or vesiculation, are a concern with the estertype local anesthetics. True allergic manifestations have been reported with procaine. The amides are essentially free of allergic properties, but suspected allergic phenomena may be caused by methylparaben, a parahydroxyben-zoic acid derivative used as an antibacterial preservative in multiple-dose vials and some dental cartridges. Esters probably should be avoided in favor of an amide when the patient has a history of allergy to a PABA-containing preparation such as certain cosmetics or sunscreens.

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