Urinary oxypurinol is a useful tool to assess adherence to allopurinol in clinical practice

Dear Editor, Gout is the most prevalent inflammatory arthritis worldwide; however, it is known that the adherence to urate-lowering therapy is often poor. The xanthine oxidase inhibitor allopurinol is the most frequently administrated drug for the treatment of gout. A systematic review of allopurinol adherence in gout has reported that 57% of patients were non-compliant with allopurinol therapy after 1 year and 77% at 5 years following the initiation of therapy [1]. Poor allopurinol adherence is a major challenge in gout management and may lead to more severe disease outcomes and increased gout-related healthcare costs. In a recent, large cohort study of factors associated with adherence to allopurinol, using data from United States Veterans Affairs national databases, it was found that older age, higher comorbidity, higher percentage of service connection, higher BMI, care at a community-based outpatient clinic or others, and rural facility location were associated with higher odds of allopurinol adherence [2]. Oxypurinol is the active metabolite of allopurinol, which is primarily eliminated unchanged by the kidneys. The measurement of plasma oxypurinol concentrations has been shown to identify low adherence to allopurinol in clinical trials [3, 4]. This study aims to evaluate adherence to allopurinol using urinary oxypurinol in a cohort of patients with gout and primary hyperuricemia.