Drug biotransformation designates the enzymatic conversion of a drug molecule into one or more metabolites within the body, a process that generally increases the polarity and water solubility of the compound and thereby facilitates its elimination in urine or bile ^[1]. The process is conventionally organized into two sequential but functionally coupled phases: phase I reactions introduce or unmask a reactive or polar functional group through oxidation, reduction, or hydrolysis, while phase II reactions conjugate the drug or its phase I metabolite with an endogenous moiety—glucuronic acid, sulfate, glutathione, or an acetyl group—yielding a product of markedly greater polarity and molecular weight ^[2][3]. The phase I oxidative reactions are catalyzed predominantly by the cytochrome P450 (CYP) superfamily, membrane-bound hemoproteins that account for the majority of oxidative drug metabolism; the principal phase II conjugating enzymes include UDP-glucuronosyltransferases (UGTs), sulfotransferases, glutathione S-transferases, and N-acetyltransferases ^[1][3]. A defining feature of drug biotransformation is that the metabolic outcome is not uniformly detoxifying: the same enzymatic transformation can convert a pharmacologically inert prodrug into its active form or generate a reactive, toxic metabolite from a stable parent compound, a phenomenon termed bioactivation ^[4]. Within pharmacogenetics and drug metabolism, the term encompasses the enzyme systems, reaction types, and metabolic pathways that collectively determine a drug’s pharmacokinetic profile, its duration of action, and its potential for toxicity, together with the genetic and environmental factors that produce interindividual variability in these pathways ^[1][5].