Which statements about phase I metabolism are true?

• A. I ONLY
• B. II ONLY
• C. III ONLY
• D. II AND III ONLY

Answer: (D)

Phase I metabolism involves chemical changes that introduce or expose a polar functional group on the molecule, mainly through oxidation, reduction, or hydrolysis. This usually happens in the liver and serves to make the compound more water-soluble and often sets the stage for Phase II conjugation, where additional groups are attached to further increase solubility for excretion. Because Phase I focuses on modifying the molecule rather than attaching large conjugates, statements that describe creating or revealing functional groups and that Phase I often prepares the molecule for Phase II conjugation are true. A statement claiming Phase I is primarily a conjugation step would be incorrect. The combination described by II and III fits these truths, making that option the best choice.