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Metformin eGFR threshold — GPhC CRA MCQ

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HardRenal and Hepatic ImpairmentMetformin eGFR thresholdGPhC CRA

A repeat prescription includes metformin 1g twice daily for a 69-year-old man. His latest blood results show eGFR 27mL/min/1.73m2, down from 48 three months ago. He has fatigue and ankle swelling and takes furosemide. What monitoring is required?

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Correct answer: B — Urgent renal function review before further metformin supply

Metformin is generally contraindicated or requires discontinuation at low eGFR because accumulation increases lactic acidosis risk. A rapid decline in renal function and symptoms such as fatigue and ankle swelling require urgent prescriber review. Renal function is the key monitoring issue before further supply. INR, peak flow and calcium monitoring do not assess metformin safety.

Reference: BNF Metformin; NICE CKS Chronic kidney disease