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Methotrexate Drug Interaction — SCE Dermatology MCQ

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ModerateDermatopharmacologyMethotrexate Drug InteractionSCE Dermatology

A 55-year-old man with psoriasis on Methotrexate has blood tests showing a sudden rise in serum creatinine from 80 to 120 μmol/L. He has been started on a new NSAID for back pain. What is the likely explanation and action?

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Correct answer: A — NSAIDs reduce renal clearance of Methotrexate, causing accumulation and potential toxicity; stop the NSAID and recheck renal function

NSAIDs reduce renal blood flow and Methotrexate clearance (by inhibiting prostaglandin-mediated renal vasodilation and competing for tubular secretion), leading to Methotrexate accumulation and increased risk of toxicity (myelosuppression, mucositis, hepatotoxicity). This is a clinically significant and common drug interaction highlighted by NPSA/MHRA alerts. The NSAID should be stopped immediately, renal function rechecked, and FBC monitored closely for pancytopenia. Other drugs that increase Methotrexate toxicity include Trimethoprim/Co-trimoxazole, Penicillins (reduced renal excretion), Probenecid, and PPIs (at high doses). Patients on Methotrexate should carry an alert card listing important drug interactions.

Reference: BAD 2016 Methotrexate Guidelines; NPSA; BNF