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Trimethoprim and methotrexate — GPhC CRA MCQ

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HardInfectionsTrimethoprim and methotrexateGPhC CRA

A 60-year-old woman taking methotrexate 15mg once weekly for rheumatoid arthritis is prescribed trimethoprim for UTI. Her last full blood count was two months ago. What is the most important interaction to flag?

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Correct answer: C — Trimethoprim with methotrexate increases risk of bone marrow suppression

Trimethoprim and methotrexate both affect folate pathways and the combination can increase risk of serious blood dyscrasias. The pharmacist should contact the prescriber for an alternative antibiotic where appropriate. Monitoring may be required if exposure has occurred. Loss of contraceptive effect is not the key issue.

Reference: BNF