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Azathioprine myelotoxicity risk — SCE Rheumatology MCQ

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HardRheumatological PharmacologyAzathioprine myelotoxicity riskSCE Rheumatology

A patient is about to start azathioprine for connective-tissue disease. TPMT phenotyping reports absent activity. What is the safest interpretation?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Avoid azathioprine and use another agent with routine blood monitoring

Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as E

A is correct. Absent TPMT activity creates a very high risk of profound thiopurine myelotoxicity, so standard azathioprine should be avoided. B reverses the metabolic consequence. C under-reacts and removes essential surveillance. D confuses azathioprine with methotrexate. E omits full blood counts and treats one test as irrelevant rather than informative.

Reference: BSR 2025 csDMARD prescription and monitoring guideline: https://academic.oup.com/rheumatology/article/65/2/keaf522/8322743