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Metformin acute kidney injury — GPhC CRA MCQ

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HardRenal and Hepatic ImpairmentMetformin acute kidney injuryGPhC CRA

A 70-year-old with lower UTI has eGFR 24 mL/min/1.73 m² and receives nitrofurantoin modified-release 100 mg twice daily. Which pharmacokinetic concern makes this regimen unsuitable?

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Correct answer: D — Reduced renal secretion lowers urinary exposure, raising systemic toxicity risk

Nitrofurantoin requires adequate renal secretion for urinary efficacy and can accumulate when renal function is poor. A short course may sometimes be used cautiously at eGFR 30 to 44 for selected lower UTI, but eGFR 24 is below that exception and needs an alternative.

Reference: BNF: nitrofurantoin: https://bnf.nice.org.uk/drugs/nitrofurantoin/