If a large drug molecule is moved back to the nasopharyngeal region and swallowed, assuming it survives stomach acid, what happens to the concentration–time curve?

• A. Shifts right (slower onset)
• B. No change in the curve
• C. Peak concentration is decreased
• D. Shifts left (faster onset)

Answer: (D)

The key idea is that how a drug enters the bloodstream determines how quickly it appears in plasma. Nasal mucosa provides a rapid, high-blood-flow absorption route, often giving a quick rise to peak concentration. If the molecule is then moved back and swallowed, it must go through the gastrointestinal tract, where absorption is slower due to dissolution, gastric emptying, intestinal transit, and sometimes first-pass metabolism. Even if the drug survives stomach acid, the overall rate of absorption is governed by the GI tract, not the nasal mucosa. So the concentration in plasma would rise more slowly, shifting the curve to the right (slower onset) and potentially reducing the peak. The leftward shift (faster onset) would only occur if absorption were accelerated via a rapid nasal route or bypass of the GI tract, which this scenario does not preserve.