In hepatic drug metabolism (Phase I and Phase II), which statement accurately describes the function of Phase I and Phase II?

• A. Phase I conjugates drugs for excretion; Phase II introduces reactive groups
• B. Phase I stores drugs in fat; Phase II conjugates drugs for excretion
• C. Phase I introduces reactive or polar groups; Phase II conjugates drugs for excretion
• D. Phase I reduces drug activity without modification; Phase II oxidizes drugs

Answer: (C)

Hepatic drug metabolism happens in two stages: Phase I functionalizes the drug by introducing or revealing polar groups, typically through oxidation, reduction, or hydrolysis; Phase II then conjugates that product with endogenous molecules (like glucuronic acid, sulfate, or glutathione) to form a highly water-soluble compound that’s ready for excretion.

This describes why the correct statement fits best: Phase I adds reactive or polar groups, which sets up the molecule for the Phase II conjugation step that enhances excretion. The other descriptions mix up the roles—conjugation for excretion isn’t Phase I, storing in fat isn’t a metabolic function of Phase I, and Phase II doesn’t involve oxidation.