Which statement describes Phase I metabolic reactions?

Which statement describes Phase I metabolic reactions?

• A. Oxidation, reduction, hydrolysis; often CYP450-mediated
• B. Glucuronidation and sulfation
• C. Conjugation to make lipophilic
• D. Transamination

Answer: (A)

Phase I metabolic reactions involve introducing or revealing functional groups on a compound through oxidation, reduction, or hydrolysis. These processes are often catalyzed by cytochrome P450 enzymes in the liver, which perform oxidation and related transformations on a wide range of drugs and xenobiotics. The result is typically a more polar or slightly more reactive metabolite that can be further processed in Phase II or prepared for excretion. This is why the statement describing oxidation, reduction, and hydrolysis, frequently mediated by CYP450, best captures Phase I metabolism. In contrast, glucuronidation and sulfation are classic Phase II conjugation reactions that add polar groups to already-modified molecules; conjugation to make lipophilic is the opposite of what Phase II does, and transamination is not a primary Phase I pathway for drug metabolism.

Phase I metabolic reactions involve introducing or revealing functional groups on a compound through oxidation, reduction, or hydrolysis. These processes are often catalyzed by cytochrome P450 enzymes in the liver, which perform oxidation and related transformations on a wide range of drugs and xenobiotics. The result is typically a more polar or slightly more reactive metabolite that can be further processed in Phase II or prepared for excretion. This is why the statement describing oxidation, reduction, and hydrolysis, frequently mediated by CYP450, best captures Phase I metabolism. In contrast, glucuronidation and sulfation are classic Phase II conjugation reactions that add polar groups to already-modified molecules; conjugation to make lipophilic is the opposite of what Phase II does, and transamination is not a primary Phase I pathway for drug metabolism.