In terms of plasma concentration-time profile, IV bolus versus IV infusion, which statement is correct?

• A. Bolus causes an immediate high plasma concentration with a decline by first-order elimination; infusion yields a rising concentration to a steady-state value.
• B. Bolus yields rising concentration to steady state; infusion causes immediate peak then decline.
• C. Bolus and infusion produce identical profiles.
• D. Bolus produces no change; infusion produces a spike.

Answer: (A)

IV bolus delivers the entire dose into the bloodstream instantly, so the plasma concentration jumps to a high value at time zero and then falls as elimination removes the drug, typically following first-order kinetics. IV infusion, on the other hand, supplies drug at a constant rate over time, so the plasma concentration increases until the rate of input equals the rate of elimination, reaching a steady-state level determined by the infusion rate divided by clearance. If the infusion stops, concentration then declines with the same elimination process. Thus, a bolus gives an immediate peak followed by decline, while an infusion produces a rising concentration toward a steady-state value.