Key Principles of Pharmacology

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2. Pharmacokinetics

2.2. Distribution

It refers to how medicines are distributed throughout the body and reach their intended target. The degree of distribution depends on the medicine’s physical and chemical properties as well as its ability to penetrate cell membranes and blood vessels.

For example, not all the medicines can have an effect on the brain because only fat-soluble medicines and very small molecules are able to penetrate the blood-brain barrier (BBB).

Many medicines bind reversibly with proteins circulating in blood or plasma (Plasma Protein Binding), so the way the protein and medicine binds determines distribution and elimination rate. Only unbound or ‘free’ medicines may diffuse through capillary walls, produce a pharmacologic effect and be metabolised and excreted.