Which statement describes Phase II biotransformation?

• A. Conjugation to increase water solubility and excretion
• B. Oxidation by CYP450
• C. Dehydrogenation
• D. Dehydration

Answer: (A)

Phase II biotransformation involves conjugation reactions that attach polar groups to a xenobiotic or a Phase I metabolite, greatly increasing water solubility and promoting excretion in urine or bile. Conjugations such as glucuronidation, sulfation, glutathione conjugation, acetylation, and amino acid conjugation add hydrophilic moieties, making elimination easier. This makes the statement describe Phase II—the step that enhances solubility for excretion. By contrast, oxidation by CYP450 is a Phase I reaction that introduces or reveals functional groups but doesn’t inherently produce the highly water-soluble conjugates characteristic of Phase II. Dehydrogenation and dehydration are not standard Phase II conjugation pathways.