CYP2C9*3 carriers have an increased risk of PHT-induced SJS/TEN (OR: 4.80; 95% CI: 0.960–23.99; p = 0.056).HLA-B*56:02/04 is associated with PHT-induced DRESS/DHS (OR: 29.312; 95% CI: 1.213–707.994; p = 0.038).HLA-B*46:01 (OR: 2.341; 95% CI: 1.078–5.084; p = 0.032). This evidence concerns the gene CYP2C9 and Schwartz-Jampel syndrome.