skip to main content

Methotrexate and trimethoprim — GPhC CRA MCQ

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

HardDrug InteractionsMethotrexate and trimethoprimGPhC CRA

A patient taking methotrexate 15 mg once weekly for psoriasis is prescribed trimethoprim for UTI. Their last FBC was normal. 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: E — Increased risk of severe haematological toxicity

Trimethoprim can increase the risk of methotrexate haematological toxicity because of additive antifolate effects. This can be serious even when previous blood counts were normal. The prescription should be queried and an alternative antibiotic considered. Patients should be counselled to report mouth ulcers, bruising, sore throat or fever.

Reference: BNF; SPS