If a drug does not survive stomach acid, what is the effect on the concentration-time curve after oral administration?

If a drug does not survive stomach acid, what is the effect on the concentration-time curve after oral administration?

• A. Shift up
• B. Shift down
• C. Shift left
• D. Shift right

Answer: (B)

Gastric instability means less drug reaches the bloodstream. When stomach acid degrades part of the oral dose, the amount available for absorption drops, so the peak plasma concentration and overall exposure (AUC) are reduced. The rate of absorption for what survives often isn’t dramatically faster, so the time to peak concentration stays about the same, but the curve sits lower overall. That’s why the concentration–time profile shifts downward. If absorption were faster, you’d see a left shift; if slower, a right shift. The key idea is reduced bioavailability leads to a lower curve.

Gastric instability means less drug reaches the bloodstream. When stomach acid degrades part of the oral dose, the amount available for absorption drops, so the peak plasma concentration and overall exposure (AUC) are reduced. The rate of absorption for what survives often isn’t dramatically faster, so the time to peak concentration stays about the same, but the curve sits lower overall. That’s why the concentration–time profile shifts downward. If absorption were faster, you’d see a left shift; if slower, a right shift. The key idea is reduced bioavailability leads to a lower curve.