Rheumatology

Answer 4 Allopurinol and azathioprine. Allopurinol is the most commonly used urate-lowering drug and is generally well tolerated. However, allopurinol should be used with extreme caution in patients who are taking azathioprine. Allopurinol works by inhibiting xanthine oxidase, thus blocking purine metabolism. Azathioprine is a purine analogue that is metabolized by the xanthine oxidase pathway. Blood levels of azathioprine increase markedly in the context of allopurinol administration and can cause granulocytopenia. When allopurinol and azathioprine are administered together, the dose of azathioprine should be decreased by 50% to 75%, with close monitoring of the leukocyte count. Click here to return to the questions

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