Vd = Total amount of drug in body (Dose_IV) / Plasma concentration (C0)
pioneer
Quantitative compartment pharmacokinetics (Torsten Teorell, 1937, and clinical PK)
Core Principles & Analysis
Defined as the ratio of the total amount of drug in the body to its concentration in blood plasma (Vd = Dose / C0 after an IV bolus), Vd is an apparent proportionality constant rather than a literal anatomical volume.
Hydrophilic, ionized macromolecules or drugs tightly bound to plasma albumin (such as warfarin or monoclonal antibodies) remain confined to the vascular and extracellular fluid, yielding a small Vd of ~3 to 15 L in a 70-kg human.
Conversely, lipophilic weak bases that partition heavily into adipose tissue, muscle, or lysosomes (such as chloroquine or amiodarone) leave very low concentrations in plasma, producing an apparent Vd of hundreds to thousands of liters — far exceeding total body water (~42 L).