HLA-B and Scarring: For example, abacavir, a common anti-retroviral, causes abacavir hypersensitivity syndrome in the presence of HLA-B*5701; Allopurinol is typically a safe drug for the treatment of gout but in the presence of HLA-B*5801 is associated with an increased risk for allopurinol induced severe cutaneous adverse drug reaction (SCAR) with most serious cases developing Stevens–Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) [16].