A strong association of allopurinol-induced SJS/TEN with the HLA-B*5801 allele was observed in a Thai population. The results suggest that HLA-B*5801 is a valid genetic marker for screening Thai individuals who may be at risk for allopurinol-induced life-threatening SJS and TEN.

Summary Carbamazepine (CBZ) has been reported as the most common culprit drug for Stevens‐Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) in several Asian countries including Thailand. A strong association between HLA‐B*1502 and CBZ‐induced SJS/TEN has been reported in Han Chinese but not in Caucasian and Japanese populations. A case–control study was conducted to determine whether HLA‐B*1502 is a valid pharmacogenetic test for SJS/TEN caused by CBZ in a Thai population. Among 42 CBZ‐induced patients with SJS/TEN, 37 (88.10%) patients carried the HLA‐B*1502 while only 5 (11.90%) of the CBZ‐tolerant controls had this allele. The risk of CBZ‐induced SJS/TEN was significantly higher in the patients with HLA‐B*1502, with an odds ratio (OR) of 54.76 [95% confidence interval (CI) 14.62–205.13, p = 2.89 × 10−12]. The sensitivity and specificity of HLA‐B*1502 for prediction of CBZ‐induced SJS/TEN were 88.10%. By assuming a 0.27% as a prevalence rate of CBZ‐induced SJS/TEN in a Thai population, the positive predictive value (PPV) and negative predictive value (NPV) of the HLA‐B*1502 were 1.92% and 99.96%. Results from this study suggest that HLA‐B*1502 may be a useful pharmacogenetic test for screening Thai individuals who may be at risk for CBZ‐induced SJS and TEN.

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Neither SJS/TEN nor DRESS caused by phenytoin was significantly associated with the HLA-B*15:02. The CYP2C9*3 variant was significantly associated with phenytoin-related SJS/TEN, but not DRESS. Certain alleles of HLA, particularly HLA-B*56:02, were significantly associated with phenytoin-related SCAR in the study population.