Rivaroxaban missed dose — GPhC CRA MCQ

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HardCardiovascular TherapeuticsRivaroxaban missed doseGPhC CRA

A patient takes azathioprine 50 mg twice daily. A specialist decides allopurinol is essential and that concomitant use will continue with enhanced blood-count monitoring. What azathioprine total daily dose follows the SmPC interaction rule?

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Correct answer: B — 25 mg daily

Option B is correct: the original azathioprine total is 100 mg daily, and concomitant allopurinol requires reduction to one quarter, which is 25 mg daily. Option C is one half rather than one quarter. Option D is three quarters. Option A leaves the interacting dose unchanged. Option E doubles it. Xanthine-oxidase inhibition prevents normal thiopurine inactivation and can cause profound, sometimes fatal, marrow toxicity, so this is a specialist-managed regimen with close monitoring.

Reference: Azathioprine SmPC: https://www.medicines.org.uk/emc/product/11143/smpc