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Trimethoprim and methotrexate — GPhC CRA MCQ

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HardInfectionsTrimethoprim and methotrexateGPhC CRA

A patient taking methotrexate 15 mg once weekly for rheumatoid arthritis is prescribed trimethoprim for UTI. The patient also takes folic acid weekly. What is the most important interaction to flag?

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Correct answer: E — Flag increased risk of severe bone marrow suppression

Trimethoprim and methotrexate both affect folate pathways and can increase risk of serious bone marrow suppression. The combination should generally be avoided or specialist advice obtained. Weekly spacing does not remove the interaction.

Reference: BNF