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Metformin: safety in cardiac patients
  1. R Khurana,
  2. I S Malik
  1. Department of Cardiology, Mary Stanford Wing, St Mary’s Hospital Campus, Imperial College Healthcare NHS Trust, London, UK
  1. Correspondence to Dr I S Malik, Imperial College Healthcare NHS Trust, Praed Street, London W2 1NY, UK; iqbal.malik{at}


Metformin is a biguanide, insulin sensitiser that reduces blood sugar levels. There are concerns about the risk of lactic acidosis in patients receiving metformin who have procedures requiring iodinated contrast, and in those with renal impairment or heart failure. The data on which these concerns are based are reviewed, with the conclusion that metformin treatment is rarely to blame for lactic acidosis. A generic policy of stopping metformin 48 h before and 48 h after the procedure in all patients is counterintuitive, lacks any evidence base and does not conform to the principles of best practice. In patients with heart failure, although the underlying condition can predispose to lactic acidosis, existing evidence suggests that metformin use is associated with improved outcome rather than increased risk.

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  • Funding From the Biomedical Research Council (BRC).

  • Competing interests None declared.

  • Provenance and Peer review Not commissioned; not externally peer reviewed.