Which is a potential reason for permeability limitation at the cell membrane?

Which is a potential reason for permeability limitation at the cell membrane?

• A. Not permeable membrane
• B. High interstitial fluid protein binding
• C. Adequate membrane transporters
• D. High perfusion to tissue

Answer: (A)

When a drug needs to cross a cell membrane, its ability to permeate depends on whether the membrane allows it to pass. If the membrane itself is not permeable to the molecule, crossing into the cell is limited, so permeability becomes the bottleneck in absorption or distribution. Other options don’t create this barrier: high interstitial fluid protein binding reduces the amount of drug free to diffuse but doesn’t change the membrane’s permeability itself; having adequate transporters would facilitate crossing rather than hinder it; and high tissue perfusion generally helps deliver drug and maintain the gradient. So the perennial reason for permeability limitation is a membrane that is not permeable to the drug.

When a drug needs to cross a cell membrane, its ability to permeate depends on whether the membrane allows it to pass. If the membrane itself is not permeable to the molecule, crossing into the cell is limited, so permeability becomes the bottleneck in absorption or distribution. Other options don’t create this barrier: high interstitial fluid protein binding reduces the amount of drug free to diffuse but doesn’t change the membrane’s permeability itself; having adequate transporters would facilitate crossing rather than hinder it; and high tissue perfusion generally helps deliver drug and maintain the gradient. So the perennial reason for permeability limitation is a membrane that is not permeable to the drug.