XDH and gout: This is supported by evidence suggesting that high doses of allopurinol will result in non competitive inhibition of xanthine oxidase (the rate-limiting enzyme in purine catabolism) [20], and the fact that many gout patients are treated with too low doses of allopurinol [21], which also seems to be the case in this study population with an average allopurinol intake below 140 mg daily.