XDH and gout: Although compounds A and B share structure similarity with febuxostat, the serum urate-lowering and anti-gout effects of these tested compounds were assessed against allopurinol for the following reasons; first, allopurinol is a purine analog and inhibits XOD via dose-dependent competition, second, allopurinol primary metabolite is oxypurinol, which is also a xanthine oxidase inhibitor with a half-life of 15 to 18 h.