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Azathioprine and allopurinol — GPhC CRA MCQ

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HardDrug InteractionsAzathioprine and allopurinolGPhC CRA

A 42-year-old man on azathioprine for ulcerative colitis presents with diarrhoea and fever after starting allopurinol for gout 5 days ago. His GP asks whether to continue both medicines. What is the most important interaction to flag?

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Correct answer: B — Allopurinol can markedly increase azathioprine toxicity

Allopurinol inhibits xanthine oxidase and can greatly increase exposure to azathioprine metabolites. This may cause severe bone-marrow suppression and infection risk. The prescriber should be contacted urgently; co-prescribing requires major azathioprine dose reduction and specialist supervision.

Reference: BNF