For a weak base with shorter gastric emptying time, what is the expected shift of the CT curve?

• A. Height increase
• B. Left shift
• C. No change
• D. Right shift

Answer: (B)

When a weak base is given, the rate at which it reaches the systemic circulation depends on how quickly it moves from the stomach to the intestine, where absorption is more favorable. The stomach’s acidic environment protonates the base, making it less permeable there, so the main absorption occurs in the higher pH environment of the small intestine. If gastric emptying time is shorter, the drug arrives at the absorption site sooner and is absorbed more quickly, causing the concentration in plasma to rise earlier. In a concentration–time (CT) curve, this faster absorption shows up as a leftward shift—the curve reaches higher levels sooner, with an earlier Tmax. The peak height might change as well, but the defining change for faster absorption is the left shift. A right shift would imply slower absorption, and no change would ignore the faster transit.