Which option lists the four primary pharmacokinetic processes?

• A. Absorption, Distribution, Metabolism, and Excretion (ADME).
• B. Absorption, Metabolism, Distribution, and Bioavailability.
• C. Distribution, Metabolism, Excretion, and Clearance.
• D. Absorption, Excretion, Distribution, and Bioavailability.

Answer: (A)

The four primary pharmacokinetic processes are Absorption, Distribution, Metabolism, and Excretion. This ADME framework describes the path of a drug from administration to elimination. Absorption is how the drug enters the bloodstream, Distribution covers how it moves from blood to tissues, Metabolism (biotransformation) changes the drug to more water-soluble forms, and Excretion eliminates it from the body. Bioavailability, the fraction of the dose that reaches systemic circulation, is not a separate process but a property that reflects absorption and first-pass effects. Clearance is a PK parameter that measures the rate of elimination, not a distinct process itself. The option that lists Absorption, Distribution, Metabolism, and Excretion aligns exactly with these four fundamental steps.