skip to main content

Methotrexate and trimethoprim — GPhC CRA MCQ

Instant feedback + full explanation. One question, done properly.

HardDrug InteractionsMethotrexate and trimethoprimGPhC CRA

A GP asks about prescribing trimethoprim for UTI to a 59-year-old woman taking methotrexate 15 mg once weekly for rheumatoid arthritis. Her latest FBC is stable and eGFR is 58 mL/min/1.73 m2. What is the most important interaction to flag?

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

Reveal the answer and explanation

Correct answer: A — Trimethoprim increases risk of methotrexate-related bone marrow suppression

Trimethoprim and methotrexate have additive antifolate effects and can increase the risk of serious bone marrow suppression. Renal impairment further increases risk, even if modest. The GP should consider an alternative antibiotic and ensure appropriate safety-netting and monitoring.

Reference: BNF; SPS