Cytochrome P450 2C9, Cytochrome P450 2C8, Cytochrome P450 3A (including main isoforms CYP3A4 and CYP3A5) (CYP2C9, CYP2C8, CYP3A)

CYP2C9, CYP2C8, and CYP3A (mainly CYP3A4/5) are members of the cytochrome P450 superfamily, a large family of monooxygenase enzymes. They are predominantly expressed in the liver and play major roles in the **oxidative metabolism** of a wide variety of pharmaceutical agents and endogenous compounds. CYP3A is the most abundant CYP enzyme in the liver and small intestine, responsible for metabolizing ~30–50% of all clinically used drugs; CYP2C9 and CYP2C8 together account for a substantial portion of phase I drug metabolism, often handling drugs with narrow therapeutic indexes. Variations in their activity, due to genetic or environmental factors, constitute an important source of **inter-individual differences** in drug response and can significantly affect safety and efficacy of therapies. Polymorphisms and regulatory mechanisms (inhibition, induction, DDIs) underlie much of the clinical pharmacology and risk associated with drugs interacting with these enzymes

Other names

Cytochrome P450 2C9Cytochrome P450 2C8Cytochrome P450 3A (most often refers to CYP3A4 and CYP3A5)

Substrate oxidation (hydroxylation, dealkylation, epoxidation)\nDrug activation or inactivation **via metabolic transformation**\nSite of **drug-drug interactions** (CYP inhibition, induction, competitive substrate binding)