Which pharmacokinetic process is defined as the diffusion of a drug into body tissues?

Which pharmacokinetic process is defined as the diffusion of a drug into body tissues?

• A. Distribution
• B. Metabolism
• C. Excretion
• D. Absorption

Answer: (A)

Distribution describes the movement of a drug from the bloodstream into tissues and organs. It often occurs by diffusion across capillary walls, driven by concentration gradients, and is shaped by tissue blood flow, capillary permeability, and the drug’s properties such as lipophilicity, molecular size, ionization, and how much binds to plasma proteins. This step is distinct from absorption (entry into the circulation from the administration site), metabolism (chemical modification, mainly in the liver), and excretion (elimination from the body). So, diffusion into body tissues is the distribution phase.

Distribution describes the movement of a drug from the bloodstream into tissues and organs. It often occurs by diffusion across capillary walls, driven by concentration gradients, and is shaped by tissue blood flow, capillary permeability, and the drug’s properties such as lipophilicity, molecular size, ionization, and how much binds to plasma proteins. This step is distinct from absorption (entry into the circulation from the administration site), metabolism (chemical modification, mainly in the liver), and excretion (elimination from the body). So, diffusion into body tissues is the distribution phase.