Which of the following regarding the influence of pH on drug passage through membranes is INCORRECT?

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Question restatement: The prompt asks which statement about how pH influences a drug's ability to pass through membranes is INCORRECT.
Option 1: 'The lipid bilayer creates a barrier between compartments' This is true in general: the lipid bilayer is the primary diffusion barrier to many drugs, especially charged species, so this statement is correct.
Option 2: 'pH may differ between compartments' This is a correct observation in many physiological situations (e.g., stomach vs plasma). Different pH values shift the ionization state of weak acids/bases, affecting membrane passage, so this option is correct.
Option 3: 'Only the charged form will pass through the membrane' This is incorrect. In most cases, the uncharged (nonionized) form is the species that readily diffuses across lipid membranes. The charged form has reduced permeability due to poor lipid solubility. Therefore, this statement is the INCORRECT one.
Option 4: 'Each compartment will have its own equilibrium' Indeed, if pH differs between compartments, each side will establish its own ionization equilibrium for the drug, influencing the fraction uncharged available to diffuse. This statement is correct.
In summary, the plausible mechanistic ideas are that the membrane is a lipid barrier, pH differences alter ionization states, each side maintains its own equilibrium, and only the uncharged form generally crosses the membrane well. The assertion that only the charged form passes through contradicts the established understanding of membrane permeability.

PCOL2021 2025 Practice MCQ Section A - 2025

Which of the following regarding the influence of pH on drug passage through membranes is INCORRECT?

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