Which class of local anesthetics is primarily metabolized by the liver?

• A. Ester local anesthetics.
• B. Amide local anesthetics.
• C. Vasoconstrictors.
• D. Opioids.

Answer: (B)

Amide local anesthetics are primarily metabolized by the liver because their chemical structure directs them to hepatic enzymes for breakdown. The amide linkage is cleaved mainly by hepatic cytochrome P450 enzymes and related amidases, so liver function strongly influences their clearance and duration of action. In contrast, ester local anesthetics are rapidly hydrolyzed in the blood by plasma cholinesterases (pseudocholinesterase) and tissue esterases, so their metabolism relies less on the liver. This is why liver disease can prolong the effect of amide anesthetics, whereas esters tend to be broken down quickly in the plasma. Examples of amide anesthetics include lidocaine, mepivacaine, bupivacaine, and prilocaine; esters include procaine, benzocaine, and tetracaine. Vasoconstrictors and opioids are not local anesthetic classes and aren’t defined by hepatic metabolism in the same way.