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MTX Pancytopenia Emergency — SCE Rheumatology MCQ

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HardRheumatology EmergenciesMTX Pancytopenia EmergencySCE Rheumatology

A patient taking weekly methotrexate develops an uncomplicated lower urinary-tract infection. Renal function and blood count are normal, and trimethoprim is proposed. Which prescribing decision is safest?

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

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Correct answer: A — Avoid trimethoprim and select a culture-directed non-antifolate antibiotic

Trimethoprim and co-trimoxazole can produce severe additive antifolate marrow toxicity with methotrexate, sometimes after treatment has ended. A suitable non-antifolate antibiotic should be selected from the infection syndrome, renal function, allergy history and culture result.

Reference: BNF: methotrexate (Current BNF monograph, accessed 30 July 2026): https://bnf.nice.org.uk/drugs/methotrexate/; BNF: trimethoprim (Current BNF monograph, accessed 30 July 2026): https://bnf.nice.org.uk/drugs/trimethoprim/