Which cellular transporters decrease drug absorption and promote drug efflux across biological barriers?

• A. Efflux transporters
• B. Influx transporters
• C. P-glycoprotein transporters
• D. Regulatory transporters

Answer: (A)

Efflux transporters actively pump drugs out of cells using energy, which lowers how much drug gets absorbed from the gut and promotes removal of drugs across barriers like the intestinal lining and the blood–brain barrier. This pumping action reduces net absorption and limits central exposure, contributing to lower bioavailability. A well-known example is P-glycoprotein, a key efflux transporter at these barriers. Influx transporters do the opposite—move drugs into cells to increase absorption—so they wouldn’t decrease absorption. Regulatory transporters isn’t a standard category describing this function.