Description Xanthine oxidase inhibitor, In hyperuricemia in gout or during cancer chemotherapy. Mechanism of Action of Allopurinol It inhibits an enzyme xanthine oxidase that is necessary to form uric acid (the enzyme catalyzing the conversion of hypoxanthine to xanthine, and xanthine to uric acid), a substance present in abnormally large amounts in the blood of persons with gout that forms solid deposits in the joints, the kidneys, and other tissues Indications for Allopurinol 1. Primary hyperuricaemia of Gout. 2. Secondary hyperuricaemia due to myeloid metaplasia, radiation, cancer chemotherapy, thiazide diuretics. 3. Prevention of uric acid nephropathy. Contra-indications of Allopurinol 1. Hypersensitivity to the drug. 2. Acute gout. 3. Hemochromatosis.