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Methotrexate and co-trimoxazole — GPhC CRA MCQ

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HardDrug InteractionsMethotrexate and co-trimoxazoleGPhC CRA

A patient taking weekly methotrexate is prescribed co-trimoxazole for a chest infection. They are due methotrexate tomorrow. What is the most important interaction to flag?

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

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Correct answer: C — Severe bone marrow suppression risk

Co-trimoxazole and methotrexate have additive antifolate effects and can cause life-threatening marrow suppression. The prescription should be queried urgently. In this scenario, the correct option is severe bone marrow suppression risk. The other options are plausible but do not address the key clinical, legal or safety issue as directly. This aligns with UK pharmacy practice guidance cited in the reference field.

Reference: BNF; Stockley's Drug Interactions