Distribution, in the field of pharmacokinetics, refers to how a drug distributes itself throughout the tissues of the body. The process of distribution is usually quantified via two measurements: protein binding and volume of distribution (Vd).
The volume of distribution is a fairly abstract concept but it is basically a measure of how efficiently the drug diffuses into the tissues as it gives a theoretical volume (in litres usually) as to how much plasma fluid would be required in order for an initial dose of the drug to be uniformly distributed at the concentration present in their plasma.
In the bloodstream drugs can either be found in their free form, usually dissolved in the water component of the blood, or bound to the proteins found in the blood's plasma (the clear liquid component of the blood).The percentage of the drug present in the bloodstream that is bound to plasma proteins is called the protein binding of the drug. This percentage is particularly relevant when people have kidney failure and are receiving dialysis, as dialysis is unable to eliminate the drug if it is highly protein bound. As drugs compete for plasma proteins and their binding sites this can also mean that one highly protein bound drug may unbind another protein bound drug, hence increasing the % of the drug present in the plasma, which could increase the effect of said drug.
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Brunton, LL; Chabner, BA; Knollmann, BC, ed. (2010). "Chapter 2. Pharmacokinetics: The Dynamics of Drug Absorption, Distribution, Metabolism, and Elimination". Goodman & Gilman's Pharmacological Basis of Therapeutics (12th ed.). New York, USA: McGraw-Hill Professional. ISBN 978-0-07-162442-8.