AUC is inversely related to clearance for a given dose.

• A. Increasing CL decreases AUC.
• B. Increasing CL increases AUC.
• C. AUC is independent of CL.
• D. AUC is proportional to Vd.

Answer: (A)

The key idea is that total systemic exposure (AUC) for a fixed dose depends on how quickly the drug is cleared from the body. Clearance is the volume of plasma cleared per unit time, so it determines the rate of elimination. For an IV dose, AUC equals Dose divided by Clearance (AUC = Dose/CL). If you increase clearance, you remove the drug more rapidly, leaving less drug in the system over time, which reduces the area under the concentration–time curve. Conversely, if clearance is lower, the drug stays in the circulation longer and AUC increases. In routes other than IV, AUC is F*Dose/CL, so as long as bioavailability F is constant, AUC still falls with higher clearance. Volume of distribution Vd describes how the drug distributes between compartments but does not directly set the total exposure when clearance is fixed, so AUC is not proportional to Vd. This is why increasing clearance decreases AUC for a given dose.