Allopurinol – Allopurinol Side Effects, Allopurinol Gout Allopurinol inhibits xanthine oxidase, the enzyme responsible for conversion of hypoxanthine to xanthine and then to uric acid. About 20% is excreted in the feces. Allopurinol is essentially cleared by glomerular filtration, whereas oxipurinol is reabsorbed in the kidney tubules. How to Take Allopurinol Take Allopurinol [...]