A drug X is a weak acid. The patient has an increased gastric emptying rate. How will the concentration-time curve be affected?

A drug X is a weak acid. The patient has an increased gastric emptying rate. How will the concentration-time curve be affected?

• A. Shifts downward
• B. Shifts upward
• C. Shifts to the left
• D. Shifts to the right

Answer: (A)

For a weak acid, ionization depends on the pH of the environment. In the acidic stomach, the drug is largely non‑ionized and crosses membranes readily, so absorption is favored there. If gastric emptying is faster, the drug spends less time in the stomach and is delivered to the higher-pH intestine more quickly. In the intestine, the weak acid becomes ionized, reducing its ability to permeate the intestinal lining and lowering the overall amount that gets absorbed. The result is a smaller amount reaching the systemic circulation, so the concentration-time curve decreases in magnitude. This downward shift reflects lower peak concentrations and usually a lower overall exposure. The other patterns would imply faster or more extensive absorption or higher concentrations, which doesn’t match the reduced absorption caused by rapid transit to a more alkaline environment.

For a weak acid, ionization depends on the pH of the environment. In the acidic stomach, the drug is largely non‑ionized and crosses membranes readily, so absorption is favored there. If gastric emptying is faster, the drug spends less time in the stomach and is delivered to the higher-pH intestine more quickly. In the intestine, the weak acid becomes ionized, reducing its ability to permeate the intestinal lining and lowering the overall amount that gets absorbed. The result is a smaller amount reaching the systemic circulation, so the concentration-time curve decreases in magnitude. This downward shift reflects lower peak concentrations and usually a lower overall exposure. The other patterns would imply faster or more extensive absorption or higher concentrations, which doesn’t match the reduced absorption caused by rapid transit to a more alkaline environment.