Pharmacology of local anesthetic agents.

Local anesthetic agents may be classified according to their intrinsic anesthetic potency and duration of activity. Procaine and chloroprocaine are relatively weak, short-acting drugs. Lidocaine, mepivacaine, and prilocaine represent agents of intermediate potency and duration of action. Tetracaine, bupivacaine, and etidocaine are highly potent, long-acting agents. The toxicity of local anesthetic drugs is usually due to inadvertent rapid intravascular injection or extravascular administration of an excessive amount. Intravascular toxicity is correlated with intrinsic anesthetic potency, whereas toxicity following extravascular injections is a function of physiological disposition characteristics of the various agents, such as rate of vascular absorption, rate of tissue redistribution, and rate of metabolism. The central nervous system is most susceptible to the toxic effects of local anesthetic agents. Signs and symptoms of CNS excitation followed by depression are the most common manifestations of local anesthetic toxicity. Cardiovascular depression may also occur following administration of excessive doses of local anesthetic agents or following high spinal or epidural anesthesia.