Ion trapping can occur when drugs ionize in compartments with different pH. Which statement correctly describes this phenomenon?

Ion trapping can occur when drugs ionize in compartments with different pH. Which statement correctly describes this phenomenon?

• A. Weak bases ionize in acidic compartments, increasing permeability
• B. Weak bases do not ionize in any compartment
• C. Ion trapping increases membrane permeability
• D. Weak bases or acids can become ionized in certain compartments (e.g., acidic stomach, basic plasma), reducing membrane permeability and trapping in compartments, altering distribution and elimination

Answer: (D)

Ion trapping happens when a drug’s ionization state changes with the pH of a compartment, and ionized forms cross membranes poorly. The non-ionized form can diffuse across membranes easily, but once the drug enters a compartment where the pH shifts its ionization toward the charged form, its permeability drops and it gets stuck there. This means both weak bases and weak acids can be trapped in different places: bases become ionized in acidic environments (like the stomach) and acids become ionized in basic environments (like plasma), reducing membrane permeability and retaining the drug in that compartment. This trapping alters how the drug distributes through tissues and how it is eliminated. The other statements fail because ionization does occur for bases in certain compartments, ionized forms do not increase permeability, and trapping is not limited to bases alone.

Ion trapping happens when a drug’s ionization state changes with the pH of a compartment, and ionized forms cross membranes poorly. The non-ionized form can diffuse across membranes easily, but once the drug enters a compartment where the pH shifts its ionization toward the charged form, its permeability drops and it gets stuck there. This means both weak bases and weak acids can be trapped in different places: bases become ionized in acidic environments (like the stomach) and acids become ionized in basic environments (like plasma), reducing membrane permeability and retaining the drug in that compartment. This trapping alters how the drug distributes through tissues and how it is eliminated. The other statements fail because ionization does occur for bases in certain compartments, ionized forms do not increase permeability, and trapping is not limited to bases alone.