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Trimethoprim-associated hyperkalaemia in CKD during ACE inhibitor treatment — MSRA MCQ

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ModerateNephrologyTrimethoprim-associated hyperkalaemia in CKD during ACE inhibitor treatmentMSRA

A 72-year-old woman with CKD G3b A3 due to hypertensive kidney disease is reviewed following routine blood tests. She takes ramipril 10 mg once daily, which is the highest tolerated dose, for hypertension and albuminuria. Her eGFR has been stable at 39–42 mL/min/1.73 m² for 9 months and her potassium was 4.7 mmol/L 2 weeks ago. Five days ago, she was prescribed trimethoprim for uncomplicated cystitis. Her urinary symptoms have resolved. She is clinically well and euvolaemic, with BP 128/72 mmHg. She has no weakness, palpitations, vomiting or diarrhoea. She is not taking NSAIDs, potassium supplements, a potassium-containing salt substitute, an MRA or a diuretic. Blood results show potassium 5.8 mmol/L, creatinine 134 micromol/L (baseline 131 micromol/L), bicarbonate 25 mmol/L and eGFR 40 mL/min/1.73 m². The sample is non-haemolysed and a same-day ECG shows no hyperkalaemic changes. What is the most appropriate management now?

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

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Correct answer: C — Stop trimethoprim, assess for other potassium-raising factors, and recheck serum potassium while continuing ramipril

Explanation lettering: B = shown as A · D = shown as B · E = shown as C · C = shown as D · A = shown as E

This is moderate, confirmed hyperkalaemia without ECG changes, acidosis, acute kidney injury or clinical instability. The temporal relationship, stable creatinine and recognised interaction make trimethoprim the most likely reversible contributor. Trimethoprim can raise potassium, particularly in people with renal impairment taking a renin–angiotensin system inhibitor. NICE advises that, when hyperkalaemia limits renin–angiotensin system antagonist use, other factors promoting hyperkalaemia should first be identified and treated, with potassium then rechecked. NICE specifies stopping the renin–angiotensin system antagonist when potassium reaches 6.0 mmol/L or more after other potassium-raising medicines have been discontinued. A is premature because ramipril provides renal and cardiovascular benefit and potassium is below the NICE threshold for stopping it. B would be appropriate with severe hyperkalaemia, ECG abnormalities, symptoms or other features requiring urgent treatment, none of which are present. C is inappropriate because NICE technology appraisal recommendations for patiromer require persistent hyperkalaemia with confirmed potassium of at least 6.0 mmol/L in the relevant CKD population. D may lower potassium but is not indicated in a euvolaemic patient and does not address the likely drug cause.

Reference: NICE NG203: Chronic kidney disease: assessment and management (2021) — https://www.nice.org.uk/guidance/ng203/chapter/Recommendations Trimethoprim 50 mg/5 ml Suspension: Summary of Product Characteristics (2026) — https://www.medicines.org.uk/emc/product/4566/smpc ACE inhibitors and angiotensin II receptor blockers monitoring (12 August 2026) — https://sps.nhs.uk/monitorings/ace-inhibitors-and-angiotensin-ii-receptor-blockers-monitoring/