Besides the kidneys, which routes are used for excretion?

• A. Liver (bile), feces, lungs, saliva
• B. Heart and muscle
• C. Brain and spinal fluid
• D. Skin and hair

Answer: (A)

Non-renal excretion mainly happens through routes that move drug or metabolite out of the body via bile into the intestines, through the lungs by exhalation, or via saliva. The liver releases metabolites into bile, which goes into the digestive tract and is eliminated in feces. Some drugs or metabolites are volatile enough to be exhaled, so the lungs serve as a exit route. Saliva can carry drug molecules that are then swallowed or further eliminated in the GI tract. In contrast, the heart and muscles are primarily distribution sites, not excretion pathways; the brain and spinal fluid are compartments with limited excretion routes; and while the skin can excrete some substances through sweat, it is a minor route compared with biliary and pulmonary routes (and hair is not a typical excretion pathway for most drugs). So the combination of biliary/fecal, pulmonary, and salivary excretion best fits non-renal elimination.