Phase I metabolism

"Phase I metabolism" does not refer to a specific molecule, receptor, enzyme, or drug target; rather, it denotes a class of metabolic biochemical reactions—primarily oxidation, reduction, and hydrolysis—that are responsible for modifying xenobiotics (such as drugs) in the body[1][2][3][4][5][6][8]. The central function of Phase I metabolism is to introduce or unmask functional groups (e.g., hydroxyl, amino, carboxyl), increasing the polarity of the compound and preparing it for further metabolism or excretion[2][3][5][8]. The major enzymes involved in Phase I metabolism are predominately members of the cytochrome P450 (CYP450) enzyme superfamily[2][3][4][5]. However, referring to "Phase I metabolism" as a single, concrete target is incorrect; it is a process involving multiple enzyme systems, particularly but not exclusively CYP450s[4][5]. Phase I metabolism does not itself act as a direct therapeutic target, nor is it a molecule or receptor to which drugs directly bind; rather, it is a collection of reaction pathways that modifies drugs and other xenobiotics in the body[4][5][2].

Other names

Phase I drug metabolismPhase 1 biotransformationPhase I reaction