Which statement best explains how a barrier like food reduces absorption?

Which statement best explains how a barrier like food reduces absorption?

• A. Food dissolves the drug in the lumen
• B. Food blocks drug molecules from reaching mucosa
• C. Food neutralizes gastric acid
• D. Food changes drug pKa dramatically

Answer: (B)

Absorption depends on drug molecules actually reaching and crossing the mucosal surface to enter the bloodstream. A meal acts as a barrier by keeping drug molecules from contacting the mucosa effectively. The presence of food can slow or limit transport to the small-intestinal lining in several ways: it delays gastric emptying so fewer molecules reach absorption sites quickly, it can bind or sequester drug molecules within the meal matrix, and it can increase the viscosity of the luminal contents, making diffusion toward the mucosa more difficult. These factors reduce the amount of free drug available to permeate the mucosa, which lowers overall absorption. The other statements don’t capture this broad mechanism. Food does not reliably dissolve the drug in a way that explains reduced absorption, and while buffering can occur, it does not universally neutralize gastric acid or dramatically change the drug’s pKa.

Absorption depends on drug molecules actually reaching and crossing the mucosal surface to enter the bloodstream. A meal acts as a barrier by keeping drug molecules from contacting the mucosa effectively. The presence of food can slow or limit transport to the small-intestinal lining in several ways: it delays gastric emptying so fewer molecules reach absorption sites quickly, it can bind or sequester drug molecules within the meal matrix, and it can increase the viscosity of the luminal contents, making diffusion toward the mucosa more difficult. These factors reduce the amount of free drug available to permeate the mucosa, which lowers overall absorption.

The other statements don’t capture this broad mechanism. Food does not reliably dissolve the drug in a way that explains reduced absorption, and while buffering can occur, it does not universally neutralize gastric acid or dramatically change the drug’s pKa.