What does “true volume of distribution” mean in this pharmacology exercise?

Question

The true volume of distribution is:

Answer choices

1. The actual volume of body fluids in which a drug is distributed.
2. The volume of fluid in which the entire administered dose would have to be distributed to produce the same concentration as in plasma.

Explanation

In this exercise, true volume of distribution means the actual volume of the compartments containing the substance.

The second option describes the apparent volume of distribution: the amount of drug in the body divided by its plasma concentration. It is a calculated quantity and need not equal an anatomical fluid volume.

The key word is true. Without that qualifier, “volume of distribution” in pharmacokinetics usually means the apparent value.