Allopurinol is a hypoxanthine structural isomer. Allopurinol blocks the enzyme xanthine oxidase, which transforms oxypurines to uric acid. This drug reduces blood and urine uric acid concentrations by inhibiting uric acid synthesis, hence protecting against uric acid-mediated end organ damage in circumstances associated with high uric acid synthesis. Overall, Allopurinol is a xanthine oxidase enzyme inhibitor that is widely used in the treatment of chronic gout. It is one of the most efficient medications for lowering urate levels.