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Methotrexate and co-trimoxazole — GPhC CRA MCQ

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EasyDrug InteractionsMethotrexate and co-trimoxazoleGPhC CRA

A patient taking weekly methotrexate for rheumatoid arthritis is prescribed co-trimoxazole for a respiratory infection. He has mild renal impairment. What is the most important interaction to flag?

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Correct answer: B — Co-trimoxazole increases risk of methotrexate-related marrow suppression

Co-trimoxazole and methotrexate can have additive antifolate toxicity, increasing risk of serious bone marrow suppression. Renal impairment further increases concern. The pharmacist should contact the prescriber before supply.

Reference: BNF