Which property most reduces brain exposure for many drugs?

Which property most reduces brain exposure for many drugs?

• A. High plasma protein binding
• B. High lipophilicity
• C. Low molecular weight
• D. Active efflux by transporters at BBB

Answer: (D)

Active efflux by transporters at the blood-brain barrier limits how much drug actually reaches the brain. Endothelial cells in brain capillaries express pumps like P-glycoprotein, BCRP, and MRPs that actively push many drugs back into the bloodstream as soon as they cross into the barrier. This means that even drugs with good membrane permeability or small size can have their brain exposure substantially reduced if they are substrates for these efflux systems. While other factors like protein binding or lipophilicity influence distribution, the efflux pumps at the BBB broadly and directly limit brain accumulation for many drugs, making this property the most impactful factor in reducing brain exposure.

Active efflux by transporters at the blood-brain barrier limits how much drug actually reaches the brain. Endothelial cells in brain capillaries express pumps like P-glycoprotein, BCRP, and MRPs that actively push many drugs back into the bloodstream as soon as they cross into the barrier. This means that even drugs with good membrane permeability or small size can have their brain exposure substantially reduced if they are substrates for these efflux systems. While other factors like protein binding or lipophilicity influence distribution, the efflux pumps at the BBB broadly and directly limit brain accumulation for many drugs, making this property the most impactful factor in reducing brain exposure.