Risk of cutaneous adverse reactions associated with allopurinol or febuxostat in real-world patients: A nationwide study.

Aims Allopurinol carries a well-known risk of cutaneous adverse reactions (CARs). Although febuxostat, a xanthine-oxidase inhibitor with different chemical structure, has been considered an alternative to allopurinol, post-marketing case reports of life-threatening febuxostat-related CARs have been reported. We aimed to compare the risk of CARs between allopurinol and febuxostat in real-world settings and to assess the impact of the market entry of febuxostat on allopurinol use and associated CARs. Methods A nationwide study was conducted using Taiwan's National Health Insurance Research Database. In the new-user cohort study, patients who received their first prescriptions of allopurinol or febuxostat were included, and Poisson regression was used to estimate the incidence rate ratios (IRRs) of CARs. In the interrupted time series analysis, time series data on new users and incidence rate of CARs were divided into three periods based on the reimbursement scheme of febuxostat in Taiwan, and segmented regression models were used to estimate changes in both the level and trend in each period. Results We identified 526 cases of CARs with 487 among new users of allopurinol and 39 among new users of febuxostat (incidence rate: 15.37 vs 3.48 per 1000 person-years). Allopurinol was associated with higher risk of CARs (adjusted IRR 5.55, 95% CI [3.97-7.76]), mild CARs (1.86, [1.24-2.81]), severe CARs (16.75, [8.87-31.62]) and fatal CARs (16.18, [5.05-51.83]) than febuxostat. The overall incidence rates of xanthine-oxidase inhibitor-related CARs decreased from 15.28 to 14.28 per 1000 person-years after the initial reimbursement of febuxostat and further decreased to 9.46 after the reimbursement coverage of febuxostat expanded; however, the changes were not statistically significant. Conclusion Febuxostat can be considered an alternative for patients carrying risk factors for allopurinol-related CARs. However, since there were fatal cases of febuxostat-related CARs, the closely monitoring of symptoms of CARs during the initiation of febuxostat is still warranted.