Which statement about AUC and dose is true when clearance remains constant?

• A. AUC increases proportionally with dose
• B. AUC decreases
• C. AUC remains unchanged
• D. AUC increases with square of dose

Answer: (A)

With constant clearance, exposure to the drug scales directly with the dose. For an IV dose, AUC equals Dose divided by Clearance (AUC = Dose/CL); with constant CL, increasing the dose increases AUC in a linear fashion. For example, doubling the dose doubles the AUC, tripling the dose triples the AUC.

The other ideas don’t fit because a fixed clearance means there’s no change in how quickly the body eliminates the drug as you adjust the dose, so AUC won’t decrease or stay the same when you raise the dose. A dependence on the square of the dose would require nonlinear (saturable) elimination, which isn’t the case here.

So, the statement that AUC increases proportionally with dose is the correct interpretation.