Which list correctly identifies the four aspects of pharmacokinetics?

• A. Absorption, Distribution, Metabolism, Excretion
• B. Absorption, Distribution, Elimination, Excretion
• C. Absorption, Distribution, Metabolism, Bioavailability
• D. Absorption, Distribution, Metabolism, Clearance

Answer: (A)

The main concept here is the four processes that describe what the body does to a drug, known as ADME: Absorption, Distribution, Metabolism, and Excretion. Absorption covers how the drug enters the bloodstream; Distribution looks at how it moves to tissues and organs; Metabolism is about chemical changes the body makes to the drug (often in the liver); Excretion is the removal of the drug and its metabolites from the body through kidneys, bile, lungs, and other routes. This set—Absorption, Distribution, Metabolism, Excretion—is the standard framework for pharmacokinetics.

Elimination is sometimes used in broader terms to describe drug removal, which can include metabolism, so it doesn’t align as a distinct fourth step in the classic ADME sequence. Bioavailability is a measure of how much drug reaches systemic circulation, not one of the four body-process steps. Clearance is a pharmacokinetic parameter that quantifies the rate of drug removal, not a separate process in the ADME sequence.