Excretion of drugs primarily occurs through which organ?

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

Answer: (A)

The kidneys are the main route for eliminating drugs from the body through urine. Blood is filtered in the kidneys, and many drug molecules are small enough to pass into the filtrate; some drugs are also secreted into the urine by tubular cells, which increases their excretion. Pathways in the kidney let ionized or water-soluble forms be removed more readily, while highly lipophilic drugs may be reabsorbed back into the bloodstream, reducing their elimination. The liver and lungs contribute secondary routes—drugs can be metabolized in the liver and excreted into bile or worn off via the lungs, and some substances leave the body in feces or breath—but the kidneys handle the bulk of drug and metabolite clearance. Clinically, kidney function greatly influences how long a drug stays active, so dosing adjustments are often needed in renal impairment.