Distribution (pharmacology)

Distribution (pharmacology) is a crucial phase in the pharmacokinetics process, which refers to the dispersion of a drug or other substance within the body. After a drug is administered, it must be distributed to the intended site of action to exert its therapeutic effect. This process is influenced by several factors, including the drug's chemical properties, the physiology of the patient, and the route of administration.

Overview

Distribution is the process by which a drug is transported from the bloodstream to the tissues and cells of the body. This process is influenced by the drug's lipophilicity, protein binding properties, and molecular size. Drugs that are highly lipophilic and small in size can easily cross cell membranes and distribute throughout the body, while drugs that are large or highly protein-bound may have a more limited distribution.

Factors Influencing Distribution

Several factors can influence the distribution of a drug within the body. These include:

• Blood flow: Drugs are often distributed to organs with high blood flow first, such as the liver, kidneys, and heart. Organs with lower blood flow, such as muscle and fat, receive the drug more slowly.
• Plasma protein binding: Drugs can bind to proteins in the blood, which can limit their distribution. Only the unbound (free) drug can cross cell membranes and exert its effect.
• Tissue permeability: Some tissues, such as the brain, have barriers that can limit the distribution of certain drugs.
• Drug metabolism: Some drugs are metabolized in the liver before they can be distributed to the rest of the body.

Volume of Distribution

The volume of distribution (Vd) is a theoretical value that represents the volume in which a drug would need to be uniformly distributed to produce the observed blood concentration. It is used to understand the distribution of the drug in the body relative to the plasma.

See Also

• Pharmacokinetics
• Absorption (pharmacology)
• Metabolism (pharmacology)
• Excretion (pharmacology)