The majority of pharmacogenetic testing to prevent ADRs were CYP2C9 and VKORC1 testing before prescription of warfarin (14 studies) [16–29], CYP2C19 genotype screening for selection of antiplatelet therapy (i.e., clopidogrel) after percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS) patients (9 studies) [30–38], and HLA-B*58:01 screening before prescribing allopurinol in patients with gout (8 studies) [40–47]. This evidence concerns the gene CYP2C19 and gout.