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Trimethoprim and methotrexate — GPhC CRA MCQ

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ModerateInfection ManagementTrimethoprim and methotrexateGPhC CRA

A patient taking weekly methotrexate for rheumatoid arthritis presents a prescription for trimethoprim for urinary symptoms. Her last blood count was borderline low. What is the most important interaction to flag?

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Correct answer: B — Trimethoprim can increase antifolate toxicity and marrow suppression risk

Trimethoprim and methotrexate both have antifolate effects and the combination can increase risk of bone marrow suppression. The borderline blood count makes the risk more concerning. The pharmacist should query the antibiotic choice before supply.

Reference: BNF