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Methotrexate and trimethoprim — GPhC CRA MCQ

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HardDrug InteractionsMethotrexate and trimethoprimGPhC CRA

A 67-year-old woman taking methotrexate 20mg once weekly for rheumatoid arthritis is prescribed trimethoprim 200mg twice daily for UTI. Her recent bloods show neutrophils 1.8 and eGFR 46mL/min/1.73m2. What is the most important interaction to flag?

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Correct answer: E — Bone marrow suppression risk is increased with methotrexate and trimethoprim

Trimethoprim has antifolate effects and can increase the risk of serious bone marrow suppression with methotrexate. Low neutrophils and reduced eGFR add concern. The prescription should be queried urgently and an alternative antibiotic considered where appropriate. The patient should be counselled to report mouth ulcers, sore throat, bruising or infection symptoms.

Reference: BNF