Which statement best describes distribution in pharmacokinetics?

• A. Movement of a drug from systemic circulation to receptor sites on target organs
• B. Absorption from the gastrointestinal tract
• C. Metabolic conversion in the liver
• D. Excretion via the kidneys

Answer: (A)

Distribution in pharmacokinetics is the movement of a drug from the systemic circulation into tissues and receptor sites. This phase determines how quickly and to what extent a drug reaches its site of action, shaping the onset and duration of effects. Several factors influence distribution: how well the drug is carried by blood to different tissues, how easily it crosses capillary walls, the degree to which it binds to plasma proteins, and its affinity for various tissues.

It’s helpful to contrast distribution with other PK processes. Absorption is about getting the drug from its administration site into the bloodstream. Metabolism involves chemical changes, typically in the liver, that transform the drug. Excretion is the removal of the drug and its metabolites from the body, primarily through the kidneys or biliary system. The statement describes distribution because it specifically refers to the drug moving from the blood to target tissues and receptor sites.