Drug distribution and binding

The distribution of drugs in the body depends on their lipophilicity and protein binding. Low plasma binding or high tissue binding or high lipophilicity usually means an extensive tissue distribution. In pharmacokinetics, the distribution is described by the parameter V, the apparent volume of distribution. This parameter measures the relative distribution of drugs between tissue and plasma and depends on the plasma and tissue binding and the lipophilicity of the drug. If the distribution of drug throughout the body is slow, V in the terminal phase will also depend on the clearance of the drug. At equilibrium, V will theoretically not be lower than 7 L in a 70-kg person, but it has no upper limit. The extent to which a drug distributes affects the half-life of the drug and the fluctuation of the concentration at steady state on multiple dosing, but not the average steady-state concentration.