DAVID PRAGER, M.D.
To the editor: In the recently published review article concerning azathioprine (1) the authors did not mention an important drug interrelationship. In any patient who is receiving a xanthine oxidase inhibitor such as allopurinol the dose of azathioprine should be lowered to the 25% level (2). This is because inhibition of xanthine oxidase by allopurinol interferes with the metabolic degradation of both azathioprine and 6-mercaptopurine and may be associated clinically with toxic side effects.
PRAGER D. Azathioprine and Allopurinol. Ann Intern Med. ;80:427. doi: 10.7326/0003-4819-80-3-427_2
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Published: Ann Intern Med. 1974;80(3):427.
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