If a weak base spends more time in the stomach, this will shift the concentration-time curve ______.

If a weak base spends more time in the stomach, this will shift the concentration-time curve ______.

• A. Right
• B. Left
• C. No change
• D. Upward

Answer: (A)

The main idea is how gastric residence time affects the rate of absorption for a weak base. In the acidic environment of the stomach, a weak base becomes protonated and ionized, which reduces its ability to cross membranes. Because absorption is mainly happening in the small intestine, keeping the drug in the stomach delays its entry into the absorption site. This slows the overall rate of absorption, so the peak in plasma concentration is reached later and the curve shifts to later times. The overall amount absorbed may stay similar, but the timing is delayed, meaning a rightward shift. Leftward or upward shifts would imply faster absorption or higher early concentrations, which isn’t the case here. So the concentration-time curve shifts to the right.

The main idea is how gastric residence time affects the rate of absorption for a weak base. In the acidic environment of the stomach, a weak base becomes protonated and ionized, which reduces its ability to cross membranes. Because absorption is mainly happening in the small intestine, keeping the drug in the stomach delays its entry into the absorption site. This slows the overall rate of absorption, so the peak in plasma concentration is reached later and the curve shifts to later times. The overall amount absorbed may stay similar, but the timing is delayed, meaning a rightward shift. Leftward or upward shifts would imply faster absorption or higher early concentrations, which isn’t the case here. So the concentration-time curve shifts to the right.