ALLOPURINOL HYPERSENSITIVITY — HLA-B*58:01

Allopurinol Hypersensitivity — HLA-B*58:01, the allele that turns the world's most prescribed gout medication into a life-threatening Stevens-Johnson reaction, present in up to 8% of Han Chinese patients.

Whole genome sequencing provides complete HLA class I typing — covering HLA-B*58:01 and all other pharmacogenomically actionable HLA alleles simultaneously — enabling allopurinol safety assessment before the first dose.

HLA-B

About this condition

Allopurinol Hypersensitivity — HLA-B*58:01

Allopurinol is the most commonly prescribed urate-lowering therapy for gout and hyperuricemia, used by tens of millions of patients worldwide. In a subset of patients, allopurinol triggers severe cutaneous adverse reactions — allopurinol hypersensitivity syndrome (AHS), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN). The mortality rate of allopurinol-induced TEN is approximately 20-30%, and allopurinol-induced SJS accounts for a disproportionate share of all SJS cases in Southeast Asian populations, where gout is common and HLA-B*58:01 is prevalent.

HLA-B*58:01 is the primary genetic risk factor for allopurinol-induced severe cutaneous adverse reactions. The allele frequency of HLA-B*58:01 varies substantially by ethnicity: approximately 6-8% in Han Chinese, 6-8% in Thai, 3-4% in Korean, 2% in Vietnamese, less than 1% in European and African ancestry populations. In Han Chinese populations, essentially all cases of allopurinol-induced SJS/TEN occur in HLA-B*58:01 carriers — the positive predictive value is high enough that prospective HLA-B*58:01 screening programs in Taiwan have dramatically reduced allopurinol-induced SJS/TEN in that population. The mechanism involves HLA-B*58:01-mediated antigen presentation of allopurinol or its metabolites to CD8+ cytotoxic T cells.

CPIC Level A guidelines for allopurinol and HLA-B*58:01 recommend that HLA-B*58:01-positive patients be prescribed an alternative urate-lowering agent (febuxostat, probenecid, or pegloticase). For HLA-B*58:01-negative patients, allopurinol is safe to prescribe from an HLA pharmacogenomics standpoint. These guidelines have been formally adopted by regulatory agencies in Taiwan (mandatory screening before allopurinol), Thailand, and Hong Kong, with increasing adoption elsewhere as pharmacogenomics-guided prescribing infrastructure expands. In the United States, CPIC recommends testing in all patients of Asian ancestry before allopurinol initiation.

Gene locus: HLA-B (6p21.33)

HLA-B58:01 single-allele commercial tests exist for Asian populations. Whole genome sequencing adds comprehensive HLA typing — covering all pharmacogenomic HLA risk alleles (B58:01, B15:02, B57:01, A*31:01) simultaneously for complete prescribing safety across multiple drug classes.

A single HLA-B*58:01 result answers only the allopurinol question — complete HLA typing answers many more

Point-of-care HLA-B*58:01 tests are designed to answer a single pharmacogenomic question before a single drug. A patient with gout who is also on HIV therapy, epilepsy medication, or who will need chemotherapy in the future has multiple pharmacogenomic HLA questions simultaneously: HLA-B*58:01 (allopurinol), HLA-B*57:01 (abacavir), HLA-B*15:02 (carbamazepine), and HLA-A*31:01 (carbamazepine in non-Asian populations). Complete HLA typing from whole genome sequencing answers all of these questions in a single test, providing a lifetime pharmacogenomic record that covers all known and future HLA-drug associations.

Febuxostat — the alternative to allopurinol — has its own considerations that require clinical context

HLA-B*58:01 carriers who cannot take allopurinol are typically offered febuxostat (Uloric) as an alternative XO inhibitor for uric acid lowering. Febuxostat does not have HLA associations and does not cause SJS/TEN. However, febuxostat carries a warning of cardiovascular events in patients with established cardiovascular disease (based on the CARES trial), making it a less suitable alternative for some patients with cardiovascular comorbidities and gout. Providing complete HLA typing — establishing that a patient is HLA-B*58:01 positive before allopurinol is ever prescribed — allows the clinician to select febuxostat or another urate-lowering strategy from the outset, in the context of a comprehensive clinical assessment.

Allopurinol Hypersensitivity — HLA-B*58:01, the allele that turns the world's most prescribed gout medication into a life-threatening Stevens-Johnson reaction, present in up to 8% of Han Chinese patients.

Allopurinol Hypersensitivity — HLA-B*58:01

HLA-B*58:01 single-allele commercial tests exist for Asian populations. Whole genome sequencing adds comprehensive HLA typing — covering all pharmacogenomic HLA risk alleles (B*58:01, B*15:02, B*57:01, A*31:01) simultaneously for complete prescribing safety across multiple drug classes.

A single HLA-B*58:01 result answers only the allopurinol question — complete HLA typing answers many more

Febuxostat — the alternative to allopurinol — has its own considerations that require clinical context

Others in Pharmacogenomics

One test. A lifetime of answers.

HLA-B58:01 single-allele commercial tests exist for Asian populations. Whole genome sequencing adds comprehensive HLA typing — covering all pharmacogenomic HLA risk alleles (B58:01, B15:02, B57:01, A*31:01) simultaneously for complete prescribing safety across multiple drug classes.