Phase I Reactions (Nonsynthetic / Functionalization):
Chemical reactions that introduce or unmask a functional group (-{OH}, (NH)_2, (-SH) on the drug molecule to make it more polar.
Primary chemical transformations include Oxidation (most common, typically via Cytochrome P450 enzymes), Reduction, and Hydrolysis.
Phase II Reactions (Synthetic / Conjugation):
Attachment of an endogenous molecule (e.g., glucuronic acid, sulfate, methyl group, acetyl group) to the functional group to render the drug water-soluble for excretion.
Examples include Acetylation, Methylation, Sulfonation, and Glucuronidation.
