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

• A. No change in onset
• B. Slower onset with a rightward shift of the curve
• C. Faster onset with a leftward shift
• D. Increased absorption with an upward shift

Answer: (B)

Gastric emptying rate controls when a drug reaches the small intestine, the main site of absorption for most drugs. For a weak base, absorption depends more on how quickly the drug arrives at the intestine than on what happens in the stomach, where it tends to be ionized in the acidic environment. If gastric emptying is slower, the drug is released into the intestine more gradually, delaying the rate at which it enters the bloodstream. This makes the rise in plasma concentration slower and pushes the peak concentration time later, effectively shifting the concentration-time curve to the right and giving a slower onset.

The overall amount absorbed may remain similar if the drug eventually reaches the absorption window, but the onset is delayed due to the slower delivery. The other scenarios would imply a faster onset or greater absorption, which isn’t consistent with slower gastric emptying.