Category: drug_metabolism
Warfarin is a 1:1 racemate; the enantiomers clear via different CYPs. S-warfarin (3-5× more potent at VKORC1) is metabolized primarily by CYP2C9 to 7-hydroxywarfarin — this is why CYP2C9 inhibitors (fluconazole, amiodarone) raise INR more than expected for a "weak inhibition" of total warfarin. R-warfarin (less active) is metabolized by CYP1A2 and CYP3A4. The asymmetry explains why DDIs with R- vs S-selective perpetrators produce qualitatively different INR effects.