Trimethoprim Dual Creatinine Potassium Effect — ESENeph MCQ

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HardChronic Kidney DiseaseTrimethoprim Dual Creatinine Potassium EffectESENeph

Three days after starting trimethoprim, a patient with CKD has creatinine rise from 150 to 195 micromol/L and potassium rise from 4.8 to 6.0 mmol/L. Which interpretation is most accurate?

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Correct answer: B — Pseudo-creatinine rise with genuine hyperkalaemia

Trimethoprim competitively inhibits proximal tubular creatinine secretion, producing a creatinine rise without an equivalent true GFR fall. It also blocks epithelial sodium channels distally, so the associated hyperkalaemia is genuine and potentially dangerous—especially with CKD or renin–angiotensin blockade. The drug and co-medications require urgent review and potassium management. The competing options do not fit the renal phenotype, temporal relationship, treatment threshold or safety constraint described. Management still requires confirmation of current medicines, renal trajectory and relevant contraindications, followed by timely biochemical and clinical reassessment. Escalate urgently if life-threatening electrolyte disturbance, respiratory compromise, shock, neurological deterioration or a dialysis indication develops.

Reference: BNF: Prescribing in renal impairment. https://bnf.nice.org.uk/medicines-guidance/prescribing-in-renal-impairment/