A local anesthetic is a medication that causes the absence of pain sensation. When it is used on specific nerve pathways, paralysis also can be achieved. Clinical LAs belong to one of two classes: aminoamide and aminoester local anesthetics. Synthetic LAs are structurally related to cocaine.  LAs act by reversibly blocking the sodium channels of nerve fibers, thereby inhibiting the conduction of nerve impulses. All local anesthetics, with the exception of cocaine, are vasodilators. Vasodilation occurs via direct relaxation of peripheral arteriolar smooth muscle fibers. Greatervasodilator activity of a local anesthetic leads to faster absorption and, thus, shorter duration of action.