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Methotrexate Drug Interaction — SCE Rheumatology MCQ

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HardRheumatology PharmacologyMethotrexate Drug InteractionSCE Rheumatology

A patient taking low-dose methotrexate is prescribed trimethoprim for a urinary infection. What is the most important prescribing issue?

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Correct answer: C — Avoid the combination because severe antifolate marrow toxicity can occur

Trimethoprim and co-trimoxazole can cause profound marrow suppression with methotrexate through additive antifolate effects and altered handling. An alternative antibiotic should be selected whenever possible, with urgent assessment if mucositis, fever or cytopenic symptoms develop.

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