What challenge occurs if a drug is highly water-soluble but exhibits poor permeability?
Answer
It dissolves quickly but gets stuck at the absorption barrier
Drug absorption relies on a delicate balance between two properties: solubility (the ability to dissolve) and permeability (the ability to pass through biological barriers, which are largely lipid-based). If a drug possesses excellent water solubility, it will dissolve rapidly in the aqueous fluids of the gut. However, if it simultaneously suffers from poor permeability, it lacks the necessary lipophilic character to partition into and cross the lipid cell membranes lining the absorption surface. Consequently, the drug dissolves instantly but remains trapped outside the systemic circulation, unable to enter the bloodstream to exert its therapeutic effect.
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