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Trimethoprim renal and potassium risk — GPhC CRA MCQ

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ModerateRenal and Hepatic ImpairmentTrimethoprim renal and potassium riskGPhC CRA

An 82-year-old with CKD taking ramipril is prescribed trimethoprim for urinary symptoms. The latest potassium is 5.2mmol/L. What is the most important interaction to flag?

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Correct answer: C — Trimethoprim can worsen hyperkalaemia, especially with ACE inhibitors and CKD

Trimethoprim can increase potassium and the risk is greater with ACE inhibitors and renal impairment. Baseline potassium is already elevated, so the prescription should be queried. An alternative antibiotic or monitoring plan may be needed.

Reference: BNF