Which anesthetic is an ester prototype?

• A. Lidocaine
• B. Bupivacaine
• C. Mepivacaine
• D. Procaine

Answer: (D)

Local anesthetics are categorized by their chemical linkage into esters and amides. The term “ester prototype” refers to the classic ester local anesthetic that served as the standard example for this group. Procaine is that ester prototype. It was the first synthetic local anesthetic and is rapidly hydrolyzed in the plasma by cholinesterases, which generally gives it a shorter duration of action.

The other agents listed are amide-type local anesthetics. They contain an amide bond and are primarily metabolized in the liver, which typically yields a longer duration of action and a different toxicity profile. This distinction between ester and amide linkages—esters being the prototype and amides representing the other major class—explains why procaine is the ester prototype.