<prompt> Allopurinol specifically inhibitsXanthine oxidaseArginaseCarbamoyl transferaseUrease  <response>: Ans. a Xanthine oxidase. Ref. Harrisons Medicine 18th Chapter 359.ALLOPURINOL Allopurinol is competitive inhibitor of xanthine oxidase. Specific treatment of uric acid calculi requires reducing the urine uric acid concentration with a xanthine oxidase inhibitor, such as allopurinol or febuxostat. It leads to rise in levels of water-soluble compounds - xanthine hypoxanthine. It inhibits degradation of 6-MP azathioprine therefore their dose should be reduced by 75. It is used only in Chronic gout It is contraindicated in pregnancy, lactation, hypersensitive patients. 