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Metformin in renal impairment — GPhC CRA MCQ

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HardEndocrine TherapeuticsMetformin in renal impairmentGPhC CRA

A patient stable on lithium is prescribed trimethoprim for a urinary infection. She has CKD stage 3 and takes ramipril. Which additional risk most strengthens the need to query the prescription?

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Correct answer: C — Hyperkalaemia and lithium toxicity

Trimethoprim can act like a potassium-sparing diuretic and increase hyperkalaemia risk with an ACE inhibitor, particularly in CKD. It has also been associated with raised lithium concentrations and toxicity. The prescriber should review antibiotic choice, renal function, potassium and the lithium monitoring plan rather than supplying routinely.

Reference: https://bnf.nice.org.uk/interactions/