Before starting allopurinol in a patient of Han Chinese, Thai or Korean origin, testing is recommended to prevent a severe cutaneous adverse reaction. Which marker identifies patients at highest risk of allopurinol hypersensitivity syndrome?

• A HLA-B*1502 allele
• B HLA-B*5801 allele ✓
• C TPMT enzyme activity
• D HLA-DQA1*0102 allele

Explanation

HLA-B*5801 is strongly associated with allopurinol-induced Stevens-Johnson syndrome and toxic epidermal necrolysis, with markedly higher carrier frequencies in Han Chinese, Thai and Korean populations, so screening is advised before prescribing. HLA-B*1502 predicts carbamazepine-induced SJS in Han Chinese, not allopurinol reactions. TPMT status guides azathioprine dosing. HLA-DQA1*0102 has no established role in allopurinol hypersensitivity screening.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

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