Amide local anesthetics are primarily metabolized by which organ?

• A. Liver
• B. Kidney
• C. Lungs
• D. Skin

Answer: (A)

Amide local anesthetics are broken down mainly in the liver. Their amide linkage makes them resistant to rapid hydrolysis in the blood, so they rely on hepatic enzymes—primarily the cytochrome P450 system in liver cells—to metabolize them into inactive forms. Once metabolized, the resulting products are eliminated by the kidneys.

This is different from ester local anesthetics, which are largely hydrolyzed in the blood by plasma cholinesterase and then excreted by the kidneys. Clinically, liver impairment or drugs that inhibit hepatic enzymes can slow the metabolism of amide anesthetics, increasing the risk of systemic toxicity, so dosages may need adjustment.