distribution

The distribution of a drug or toxic substance within the body is a critical aspect of its action, involving its movement from the site of administration to its target site and eventual elimination. This process, known as pharmacokinetics, begins with absorption into the bloodstream.1

Distribution

Once in the bloodstream, drugs are transported to various organs, including the liver and kidneys, which are key sites for metabolism and excretion. The ability of a drug to move from the blood into tissues depends on the permeability of blood capillaries. While most capillaries allow free passage of small molecules, the blood-brain barrier, formed by tight capillary walls in the brain, significantly restricts entry, allowing primarily lipid-soluble substances to pass.23

The rate of accumulation in specific tissues is also influenced by blood flow. Organs with high blood supply, such as the liver, brain, and kidneys, reach a steady state of chemical concentration with the blood more rapidly than poorly perfused tissues like fat and bone. Some drugs bind to plasma proteins, which reduces their immediate potency but acts as a reservoir to maintain active drug levels in the blood.42