Which factors can affect the distribution of a drug?

The distribution of a drug within the body is influenced by several critical factors, among which plasma protein binding, tissue permeability, and blood flow play a significant role.

Plasma protein binding refers to how much of the drug is attached to proteins in the blood, such as albumin. When a drug is bound to plasma proteins, it is typically pharmacologically inactive and cannot exert its therapeutic effect. Only the unbound (free) portion of the drug can distribute into tissues and reach its site of action. Variations in plasma protein levels can therefore impact the extent to which a drug is available for distribution.

Tissue permeability relates to the ease with which a drug can cross cell membranes to enter various tissues. This can depend on the drug's chemical properties, such as its solubility and molecular size. Lipophilic (fat-loving) drugs may more easily permeate cell membranes than hydrophilic (water-loving) drugs, thus influencing how widely a drug can distribute throughout the body.

Blood flow is another vital factor because the rate at which blood circulates through various tissues determines how quickly a drug can be delivered to its target site. Tissues with higher blood flow, such as the liver and kidneys, will receive the drug more rapidly, whereas