Distribution

Definition

Distribution (distribution) is a pharmacokinetic process that begins immediately after absorption of the drug from the intestine. During this process, the drug enters the bloodstream and travels to organs, body fluids, and tissues. Distribution is necessary for the drug to reach its drug target at a sufficient concentration. For example, an antidepressant must be distributed across the bloodbrain barrier into the central nervous system (brain) so that it can trigger its effects at the synapses of neurons. Volume of distribution is a pharmacokinetic parameter that provides information about how much a pharmaceutical agent distributes from the blood into the extravascular space and tissues (see there). It is a theoretical quantity and not a real volume. Important influencing factors are protein binding, physicochemical properties of the drug, organ perfusion and anatomical barriers. If protein binding is high, distribution is expected to be lower because the active ingredient is primarily in the blood. This is true, for example, of vitamin K antagonists such as warfarin.