Pharmacokinetics: Calculation of Volume of Distribution

The volume of distribution (Vd) is a mathematical expression of the sum of the apparent volumes of the compartments that constitute the body. Vd relates the amount of drug in the body to the concentration of drug in the plasma. It does not necessarily refer to an identifiable physiological volume but merely to the fluid volume that would be required to account for the entire drug in the body (based on the amount found in a blood sample). Vd may be stated in Liters or in L/kg. A drug with a large Vd is bound in peripheral tissues (e.g., fat) while a drug with a small volume of distribution is primarily in plasma or body fluids (intercellular and extracellular fluids).

Examples: Gentamicin 0.31 L/kg

Diazepam 1.1 L/kg

Amitriptyline 15 L/kg

Chloroquine 200 L/kg

Category: Pharmacology Notes