Cytochrome P450 2C9 (CYP2C9) is a crucial enzyme in human drug metabolism, responsible for the metabolism of numerous drugs and xenobiotics. CYP2C9 substrates include fluoxetine, losartan, phenytoin, tolbutamide, torsemide, S-warfarin, and many non-steroidal anti-inflammatory drugs (NSAIDs). CYP2C9 activity can be induced by drugs such as rifampicin, carbamazepine, ethanol, and phenobarbitone. However, it can also be inhibited by drugs like amiodarone, fluconazole, phenylbutazone, and certain sulphonamides, leading to clinically significant drug interactions. Genetic polymorphisms in the CYP2C9 gene, particularly at amino acid residues 144 (Arg144Cys) and 359 (Ile359Leu), significantly affect CYP2C9 activity. Individuals homozygous for the Leu359 allele have significantly reduced metabolic capacities for CYP2C9 substrates, which can impact the dosage requirements and elimination rates of these drugs. The frequency of the Leu359 allele is relatively low, but it can lead to substantial differences in drug metabolism. The structure of CYP2C9 is characterized by six substrate recognition sites (SRSs), with critical residues contributing to substrate specificity. CYP2C9 is involved in the metabolism of various drugs, including tolbutamide, phenytoin, S-warfarin, and NSAIDs. The enzyme's activity is influenced by factors such as enzyme induction and inhibition, genetic polymorphisms, and age. Interindividual variability in CYP2C9 activity can result in wide differences in drug clearance and response, particularly for drugs with narrow therapeutic indices. In conclusion, CYP2C9 plays a vital role in drug metabolism, and its activity is influenced by multiple factors, including genetic variations. Understanding these factors is essential for predicting and managing drug interactions and dosing regimens.Cytochrome P450 2C9 (CYP2C9) is a crucial enzyme in human drug metabolism, responsible for the metabolism of numerous drugs and xenobiotics. CYP2C9 substrates include fluoxetine, losartan, phenytoin, tolbutamide, torsemide, S-warfarin, and many non-steroidal anti-inflammatory drugs (NSAIDs). CYP2C9 activity can be induced by drugs such as rifampicin, carbamazepine, ethanol, and phenobarbitone. However, it can also be inhibited by drugs like amiodarone, fluconazole, phenylbutazone, and certain sulphonamides, leading to clinically significant drug interactions. Genetic polymorphisms in the CYP2C9 gene, particularly at amino acid residues 144 (Arg144Cys) and 359 (Ile359Leu), significantly affect CYP2C9 activity. Individuals homozygous for the Leu359 allele have significantly reduced metabolic capacities for CYP2C9 substrates, which can impact the dosage requirements and elimination rates of these drugs. The frequency of the Leu359 allele is relatively low, but it can lead to substantial differences in drug metabolism. The structure of CYP2C9 is characterized by six substrate recognition sites (SRSs), with critical residues contributing to substrate specificity. CYP2C9 is involved in the metabolism of various drugs, including tolbutamide, phenytoin, S-warfarin, and NSAIDs. The enzyme's activity is influenced by factors such as enzyme induction and inhibition, genetic polymorphisms, and age. Interindividual variability in CYP2C9 activity can result in wide differences in drug clearance and response, particularly for drugs with narrow therapeutic indices. In conclusion, CYP2C9 plays a vital role in drug metabolism, and its activity is influenced by multiple factors, including genetic variations. Understanding these factors is essential for predicting and managing drug interactions and dosing regimens.