Which statement describes the general metabolic sites for ester and amide local anesthetics?

Which statement describes the general metabolic sites for ester and amide local anesthetics?

• A. Esters are metabolized in the liver; amides are metabolized in plasma.
• B. Both esters and amides are metabolized in the liver.
• C. Esters are metabolized in plasma via esterases, and amides are metabolized in the liver.
• D. Both esters and amides are metabolized in plasma.

Answer: (C)

Ester-type local anesthetics are rapidly hydrolyzed in the bloodstream by plasma esterases (such as pseudocholinesterase), so they are inactivated quickly after administration. Amide-type anesthetics, on the other hand, are primarily metabolized in the liver by hepatic amidases and related enzymes, which makes their duration longer and more influenced by liver function. For example, procaine (an ester) is quickly broken down in plasma, while lidocaine (an amide) is mainly processed in the liver. This distinction—plasma metabolism for esters versus hepatic metabolism for amides—explains their different durations and handling in patients with liver disease or altered blood flow.

Ester-type local anesthetics are rapidly hydrolyzed in the bloodstream by plasma esterases (such as pseudocholinesterase), so they are inactivated quickly after administration. Amide-type anesthetics, on the other hand, are primarily metabolized in the liver by hepatic amidases and related enzymes, which makes their duration longer and more influenced by liver function. For example, procaine (an ester) is quickly broken down in plasma, while lidocaine (an amide) is mainly processed in the liver. This distinction—plasma metabolism for esters versus hepatic metabolism for amides—explains their different durations and handling in patients with liver disease or altered blood flow.