Compared to oral administration, an intramuscular injection typically produces which shift in the concentration-time curve?

Compared to oral administration, an intramuscular injection typically produces which shift in the concentration-time curve?

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

Answer: (B)

The key idea is that how fast the drug is absorbed shapes where the curve appears along the time axis. Intramuscular injection delivers drug into a well‑perfused tissue, so it enters the bloodstream more quickly than a drug taken orally, which must dissolve in the gut, pass through the intestinal wall, and often undergo first‑pass metabolism. Because of this faster entry into systemic circulation, the concentration of drug in plasma rises sooner, reaching a given level earlier. That makes the concentration–time curve move to the left compared with oral administration. In practice, Tmax tends to be shorter (and Cmax may be higher) for IM than for oral, reflecting faster absorption.

The key idea is that how fast the drug is absorbed shapes where the curve appears along the time axis. Intramuscular injection delivers drug into a well‑perfused tissue, so it enters the bloodstream more quickly than a drug taken orally, which must dissolve in the gut, pass through the intestinal wall, and often undergo first‑pass metabolism. Because of this faster entry into systemic circulation, the concentration of drug in plasma rises sooner, reaching a given level earlier. That makes the concentration–time curve move to the left compared with oral administration. In practice, Tmax tends to be shorter (and Cmax may be higher) for IM than for oral, reflecting faster absorption.