{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n CYP2C19 is a key liver enzyme of the cytochrome P450 family that plays a central role in the bioactivation of several prodrugs, most notably clopidogrel. Many studies have shown that clopidogrel requires conversion by CYP2C19 into its active thiol metabolite in order to achieve effective antiplatelet activity. Loss‐of‐function alleles (for example, CYP2C19*2, *3, and others) result in reduced conversion of clopidogrel, which leads to lower plasma levels of the active metabolite, diminished platelet inhibition, and consequently an increased risk of adverse cardiovascular events such as myocardial infarction and stent thrombosis. In contrast, the gain‐of‐function allele CYP2C19*17 increases enzyme transcription and activity; this enhanced metabolism may lead to an improved antiplatelet response but can also predispose patients to a higher risk of bleeding. Furthermore, while CYP2C19 genetic variability is critically important for the pharmacokinetics and pharmacodynamics of clopidogrel, its influence appears to be minimal for other antiplatelet agents like prasugrel, which undergo different metabolic pathways. Beyond antiplatelet therapy, CYP2C19 polymorphisms also affect the metabolism of other clinically important drugs—including proton pump inhibitors, antidepressants, and tamoxifen—thereby contributing to the interindividual variability in therapeutic outcomes and adverse event profiles. Collectively, these findings underscore the importance of CYP2C19 in determining both drug efficacy and safety and support the potential role of genotype‐guided therapy in clinical practice."}]}, {"type": "t", "text": "\n "}, {"type": "p", "children": [{"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "11"}]}, {"type": "t", "text": ""}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Jessica L Mega, Sandra L Close, Stephen D Wiviott, et al. 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