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Trimethoprim MTX Interaction — SCE Rheumatology MCQ

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HardRheumatology EmergenciesTrimethoprim MTX InteractionSCE Rheumatology

A woman taking leflunomide 20 mg daily for rheumatoid arthritis wishes to conceive without waiting for natural drug elimination. Which accelerated elimination regimen is specified in the UK SmPC?

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

Reveal the answer and explanation

Correct answer: C — Colestyramine 8 g three times daily for 11 days, then perform required teriflunomide concentration checks

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

C is correct. Leflunomide has prolonged enterohepatic recycling; the UK SmPC specifies colestyramine 8 g three times daily for 11 days, or activated charcoal 50 g four times daily for 11 days. Pregnancy planning also requires confirmation that the active metabolite is below 0.02 mg/L on two tests at least 14 days apart, followed by the specified interval before fertilisation. A and B underdose and abbreviate washout. D confuses leflunomide elimination with methotrexate rescue. E is ineffective because the active metabolite is not removed reliably by dialysis. The concentrations are not optional: an apparently completed washout course alone does not document sufficiently low fetal exposure.

Reference: UK leflunomide summary of product characteristics: https://www.medicines.org.uk/emc/product/4944/smpc