If a solid is ingested and slows gastric emptying, allowing a weak acid to remain in the stomach longer, why might absorption not always increase?

If a solid is ingested and slows gastric emptying, allowing a weak acid to remain in the stomach longer, why might absorption not always increase?

• A. Food may block the drug from reaching cells, lowering absorption
• B. The drug is degraded in the stomach
• C. Gastric pH does not affect absorption
• D. The drug is not absorbed in any case

Answer: (A)

The main idea is that absorption depends on delivering the drug to the small intestine, where most absorption takes place, and on how well the drug dissolves and diffuses to the intestinal mucosa. Even if a solid slows gastric emptying and a weak acid stays in the stomach longer, that doesn’t automatically boost absorption because the meal can physically block the drug from reaching the absorptive cells. Food can create a barrier or matrix around the drug, bind it, or otherwise reduce the free drug concentration available to diffuse to the intestinal lining, so less drug actually gets absorbed. In addition, slowing transit to the small intestine means less drug arrives at the primary absorption site within a practical time frame, which can further limit absorption. The other statements aren’t necessary to explain this scenario: gastric pH can affect dissolution and absorption for ionizable drugs, and degradation or non-absorption in all cases isn’t implied here. So the reason absorption may not increase is that food may block the drug from reaching the cells, lowering absorption.

The main idea is that absorption depends on delivering the drug to the small intestine, where most absorption takes place, and on how well the drug dissolves and diffuses to the intestinal mucosa. Even if a solid slows gastric emptying and a weak acid stays in the stomach longer, that doesn’t automatically boost absorption because the meal can physically block the drug from reaching the absorptive cells. Food can create a barrier or matrix around the drug, bind it, or otherwise reduce the free drug concentration available to diffuse to the intestinal lining, so less drug actually gets absorbed. In addition, slowing transit to the small intestine means less drug arrives at the primary absorption site within a practical time frame, which can further limit absorption. The other statements aren’t necessary to explain this scenario: gastric pH can affect dissolution and absorption for ionizable drugs, and degradation or non-absorption in all cases isn’t implied here. So the reason absorption may not increase is that food may block the drug from reaching the cells, lowering absorption.