Which is the primary site of metabolism for medications?

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

Answer: (B)

Drug metabolism is the body's process of biotransforming medications to more water-soluble forms for easier elimination. This major transformation happens in the liver, where hepatocytes are rich in enzymes, especially the cytochrome P450 family. These enzymes carry out Phase I reactions such as oxidation, reduction, and hydrolysis, often followed by Phase II conjugation (like glucuronidation or sulfation) to create polar metabolites. Because orally administered drugs pass through the liver via the hepatic portal system, the liver is exposed to high drug concentrations and can also reduce drug bioavailability through first-pass metabolism. While other organs like the kidneys mainly handle excretion and the lungs or skin can contribute to metabolism for a few drugs, they are not the primary site. Therefore, the primary site of metabolism for medications is the liver.