What is the relationship between AUC and dose for an IV bolus, and what does it imply about clearance?

• A. AUC = Dose / Vd.
• B. AUC = Dose / CL.
• C. AUC = Dose × CL.
• D. AUC = Dose × Vd.

Answer: (B)

For intravenous bolus administration under linear kinetics, total body exposure over time (AUC) reflects how quickly the drug is cleared, not how it distributes. The relationship is AUC0-∞ = Dose / CL. This comes from the fact that the body eliminates drug at a rate proportional to its concentration, so the total amount removed (the dose) divided by the clearance rate gives the integral of concentration over time.

In other words, how long the drug stays in the body (the exposure) is governed by clearance: higher clearance reduces AUC, and lower clearance increases AUC. The initial concentration after a bolus is C0 = Dose / Vd, but Vd does not enter the final AUC expression, because the AUC depends on elimination, not distribution, under these linear conditions.

The other forms would either mix in Vd inappropriately or imply that exposure rises with clearance, which would be contrary to how clearance determines how fast the drug is removed.