skip to main content

Gout in a patient receiving azathioprine — SCE Rheumatology MCQ

Instant feedback + full explanation. One question, done properly.

ModerateRheumatological PharmacologyGout in a patient receiving azathioprineSCE Rheumatology

A 54-year-old woman with systemic lupus erythematosus has recurrent crystal-proven gout. She has experienced three flares in the past year, and her serum urate is 512 micromol/L. Her latest flare settled 3 weeks ago. Renal function is stable with an eGFR of 68 mL/min/1.73 m². Lupus is quiescent on azathioprine 150 mg daily; previous mycophenolate caused severe gastrointestinal intolerance, and the multidisciplinary team considers continued azathioprine necessary. Low-dose colchicine prophylaxis has been arranged. Which is the most appropriate urate-lowering treatment plan?

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

Reveal the answer and explanation

Correct answer: B — Start low-dose allopurinol, reduce azathioprine to 25% of its current dose and monitor the full blood count frequently

Explanation lettering: D = shown as A · A = shown as D

She has multiple gout flares and should receive treat-to-target urate-lowering therapy. The previous flare settled 3 weeks ago, which is within NICE's recommended interval of at least 2–4 weeks before starting therapy; prophylaxis against mobilisation flares has also been arranged. Allopurinol inhibits xanthine oxidase, which normally contributes to the inactivation of azathioprine-derived 6-mercaptopurine. Co-administration can therefore markedly increase active thiopurine exposure and cause life-threatening myelosuppression. Although the combination should preferably be avoided, the UK product information specifies that, when co-administration is clinically necessary, azathioprine should be reduced to one-quarter of its previous dose with frequent haematological monitoring. A is unsafe because monitoring does not compensate for continuing full-dose azathioprine. C is similarly unsafe: febuxostat also inhibits xanthine oxidase and may produce severe thiopurine toxicity. D is inadequate because febuxostat–azathioprine co-administration is not recommended and, if unavoidable, current product information advises reducing azathioprine to 20% or less, not 50%. E recognises the interaction but does not reduce azathioprine sufficiently. Serum urate should subsequently be monitored and allopurinol titrated to target.

Reference: Gout: diagnosis and management — Recommendations (09 June 2022) — https://www.nice.org.uk/guidance/ng219/chapter/Recommendations Zyloric Tablets 100 mg, 300 mg — Summary of Product Characteristics (19 February 2025) — https://www.medicines.org.uk/emc/medicine/4565/SPC/Zyloric%2BTablets%2B100mg%2C%2B300mg Azathioprine 25 mg Film-Coated Tablets — Summary of Product Characteristics (30 October 2025) — https://www.medicines.org.uk/emc/product/11142/smpc