Prednisolone short course counselling — GPhC CRA MCQ
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Correct answer: B — Urgent interaction and dose review
Allopurinol inhibits xanthine oxidase, an important route of azathioprine metabolite inactivation. Standard azathioprine doses can then cause profound marrow suppression. Co-prescribing requires specialist intent, major azathioprine dose reduction and close blood monitoring; timing separation does not remove the interaction.
Reference: https://bnf.nice.org.uk/interactions/