Which organ is primarily responsible for metabolizing many drugs?

Which organ is primarily responsible for metabolizing many drugs?

• A. Kidney
• B. Lungs
• C. Liver
• D. Small intestine

Answer: (C)

Drug metabolism is carried out mainly by the liver because hepatocytes are rich in drug‑metabolizing enzymes, especially the cytochrome P450 system. These enzymes oxidize, reduce, and hydrolyze lipophilic drugs (Phase I), often making them more reactive, and then Phase II pathways add polar groups (glucuronidation, sulfation, acetylation) to further increase solubility for excretion. A key clinical point is the first-pass effect: drugs taken by mouth often pass through the liver before reaching systemic circulation, so a portion can be inactivated or activated there. Other organs do contribute in smaller ways: the kidneys focus mainly on eliminating metabolites and unchanged drugs; the lungs can metabolize a few volatile substances; and the small intestine also has enzymes that contribute to first-pass metabolism, but not to the same extent as the liver.

Drug metabolism is carried out mainly by the liver because hepatocytes are rich in drug‑metabolizing enzymes, especially the cytochrome P450 system. These enzymes oxidize, reduce, and hydrolyze lipophilic drugs (Phase I), often making them more reactive, and then Phase II pathways add polar groups (glucuronidation, sulfation, acetylation) to further increase solubility for excretion. A key clinical point is the first-pass effect: drugs taken by mouth often pass through the liver before reaching systemic circulation, so a portion can be inactivated or activated there.

Other organs do contribute in smaller ways: the kidneys focus mainly on eliminating metabolites and unchanged drugs; the lungs can metabolize a few volatile substances; and the small intestine also has enzymes that contribute to first-pass metabolism, but not to the same extent as the liver.