HLA-B and toxic epidermal necrolysis: However, it is necessary for patients to perform a PGx testing before using these drugs, for the severe adverse reactions maculopapular exanthem, Stevens-Johnson syndrome and toxic epidermal necrolysis are all related to Human leukocyte antigen B (HLA-B) genotype polymorphism (Saito et al., 2016; Phillips et al., 2018).