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Azathioprine and allopurinol — GPhC CRA MCQ

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HardDrug InteractionsAzathioprine and allopurinolGPhC CRA

A 58-year-old man with Crohn's disease takes azathioprine 150 mg daily. A GP prescription for allopurinol 300 mg daily is issued after two gout attacks. FBC last month showed WBC 4.2 x 10^9/L. What is the most important interaction to flag?

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Correct answer: E — Allopurinol can increase azathioprine toxicity and severe bone marrow suppression

Allopurinol inhibits xanthine oxidase, reducing metabolism of azathioprine metabolites and increasing risk of life-threatening myelosuppression. If co-prescribing is necessary, specialist dose reduction and close blood monitoring are required. A routine full dose of both medicines is unsafe. The pharmacist should contact the prescriber before supply.

Reference: BNF