Figure 3.

Comparison of allopurinol, oxypurinol, and febuxostat structures. Allopurinol and its long-lived major active metabolite oxypurinol (both pictured) inhibit xanthine oxidase, as does febuxostat (pictured), which, in contrast to the other two agents, does not have a purine-like backbone.

Terkeltaub Arthritis Research & Therapy 2009 11:236   doi:10.1186/ar2738
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