CYP2C9

CYP2C9 is a major cytochrome P450 enzyme in human liver and represents the most abundant functional member of the CYP2C subfamily, contributing substantially to phase I drug metabolism and xenobiotic clearance.^[1][2] Mechanistically, CYP2C9 catalyzes the oxidation of numerous clinically important substrates, including S-warfarin, phenytoin, tolbutamide, diclofenac, celecoxib, and losartan, while also participating in the metabolism of endogenous compounds such as arachidonic acid and steroids.^[2][3][4] Therefore, CYP2C9 serves as a critical regulator of drug exposure, pharmacokinetics, and metabolic homeostasis.^[1][4] In disease-relevant settings, altered CYP2C9 activity is strongly associated with variability in anticoagulant response, phenytoin neurotoxicity, and adverse reactions to nonsteroidal anti-inflammatory drugs, making the enzyme a central target in pharmacogenomic studies and precision medicine models.^[1][5][2] Compared with related CYP2C isoforms, including CYP2C8 and CYP2C19, CYP2C9 contributes a larger proportion of hepatic CYP2C-mediated drug metabolism and displays distinct substrate selectivity toward weakly acidic therapeutic compounds.^[2][4][6] Genetic polymorphisms further distinguish CYP2C9 from related isoforms, as reduced-function alleles significantly modify metabolic capacity and influence dosing requirements for multiple therapeutic agents.^[1][5] For experimental applications, selective inhibitors and inducers of CYP2C9 are widely used to investigate drug-drug interactions, enzyme regulation, substrate specificity, and metabolic liability during drug discovery and translational pharmacology studies.^[2][4]