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Allopurinol and azathioprine — GPhC CRA MCQ

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HardDrug InteractionsAllopurinol and azathioprineGPhC CRA

A patient taking azathioprine for inflammatory bowel disease is prescribed allopurinol for gout by an out-of-hours service. The pharmacy record shows no gastroenterology advice about dose reduction. What is the most important interaction to flag?

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Correct answer: E — Allopurinol can greatly increase azathioprine toxicity

Allopurinol inhibits xanthine oxidase and can markedly increase exposure to active azathioprine metabolites. Severe bone marrow suppression can occur unless azathioprine dose is substantially reduced under specialist supervision. The prescription should be queried before supply.

Reference: BNF