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Allopurinol-azathioprine interaction — SCE Rheumatology MCQ

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HardCrystal arthropathiesAllopurinol-azathioprine interactionSCE Rheumatology

A 64-year-old man with acute gout has recently started azathioprine for autoimmune hepatitis. His GP is considering urate-lowering therapy after repeated flares. Which drug interaction is most important to recognise?

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Correct answer: D — Allopurinol can markedly increase azathioprine toxicity

Xanthine oxidase inhibitors such as allopurinol and febuxostat can increase azathioprine metabolite exposure and cause severe myelosuppression unless specialist dose adjustment is made. Colchicine does not protect against this interaction. This is a common high-stakes prescribing trap in gout.

Reference: BNF; NICE NG219