Active transport can be observed at both sites of absorption and sites of elimination. True or False?

• A. True
• B. False
• C. Not applicable
• D. Depends on the drug

Answer: (A)

Active transport uses energy to move drugs against a gradient, influencing both how a drug gets absorbed and how it is eliminated. In the gut, uptake transporters can bring a drug into enterocytes, while efflux transporters can push some back into the lumen, so the net absorbed amount depends on the balance between these opposing processes. For elimination, transporters in the liver and kidneys actively move drugs into sites of excretion: in the liver, uptake transporters bring drugs into hepatocytes and efflux pumps send them into bile; in the kidneys, secretory transporters push drugs from the blood into the tubular fluid for urine. This means active transport participates in both absorption and elimination, making the statement true. (Some drugs aren’t transporter substrates and rely on passive diffusion, but the general principle remains.)