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Allopurinol and azathioprine — GPhC CRA MCQ

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HardDrug InteractionsAllopurinol and azathioprineGPhC CRA

A 43-year-old woman taking azathioprine for inflammatory bowel disease is prescribed allopurinol 300mg daily for gout. Her latest FBC is normal, and the GP asks if there is any issue before dispensing. What is the most important interaction to flag?

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Correct answer: A — Allopurinol can increase azathioprine toxicity through xanthine oxidase inhibition

Allopurinol inhibits xanthine oxidase and can markedly increase exposure to active azathioprine metabolites. This can cause severe bone marrow suppression unless the azathioprine dose is substantially adjusted under specialist advice. The pharmacist should contact the prescriber before supply.

Reference: BNF