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Metformin renal impairment — GPhC CRA MCQ

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HardEndocrine TherapeuticsMetformin renal impairmentGPhC CRA

A patient taking metformin long term develops macrocytosis, glossitis and distal paraesthesia. Which investigation should be added without automatically stopping metformin?

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

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Correct answer: A — Measure vitamin B12 and treat deficiency while therapy is reviewed

Metformin commonly lowers vitamin B12, with risk increasing at higher dose and longer duration. New megaloblastic anaemia or neuropathy should prompt B12 testing and treatment. Metformin can usually continue if otherwise suitable while the deficiency and alternative causes are addressed.

Reference: MHRA: metformin and reduced vitamin B12 levels: https://www.gov.uk/drug-safety-update/metformin-and-reduced-vitamin-b12-levels-new-advice-for-monitoring-patients-at-risk