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Azathioprine myelosuppression — SCE Rheumatology MCQ

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ModerateRheumatological pharmacologyAzathioprine myelosuppressionSCE Rheumatology

A 63-year-old man on azathioprine for connective tissue disease develops fever and sore throat two weeks after starting the drug. FBC shows neutrophils 0.4 × 10^9/L. His TPMT activity was low before treatment but this was not acted on. What is the most likely explanation?

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Correct answer: A — Azathioprine myelotoxicity

Low TPMT activity increases risk of azathioprine toxicity and severe myelosuppression. Fever with neutropenia requires urgent assessment, drug cessation and infection management. Baseline TPMT testing helps dose selection but does not replace blood monitoring.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/musculoskeletal-conditions