FIGURE 14-1 Structural formulas of selected local anesthetics. Most local anesthetics consist of a hydrophobic (aromatic) moiety (black), a linker region (light blue), and a substituted amine (hydrophilic region, in dark blue). The structures above are grouped by the nature of the linker region. Procaine is a prototypic ester-type local anesthetic; esters generally are well hydrolyzed by plasma esterases, contributing to the relatively short duration of action of drugs in this group. Lidocaine is a pro-totypic amide-type local anesthetic; these structures generally are more resistant to clearance and have longer durations of action. There are exceptions, including benzocaine (poorly water soluble; used only topically) and the structures with a ketone, an amidine, and an ether linkage. See 11th edition of the parent text, Figure 14—1, for additional details and structures.
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