Metformin, heart failure, and lactic acidosis: is metformin absolutely contraindicated?

BMJ 2007; 335 doi: (Published 06 September 2007) Cite this as: BMJ 2007;335:508
  1. A A Tahrani, specialist registrar in diabetes and endocrinology,
  2. G I Varughese, specialist registrar in diabetes and endocrinology,
  3. J H Scarpello, consultant physician,
  4. F W F Hanna, consultant physician in diabetes and endocrinology
  1. Department of Diabetes and Endocrinology, University Hospital of North Staffordshire, Stoke-on-Trent ST4 6QG
  1. Correspondence to: A A Tahrani abdtahrani{at}
  • Accepted 23 April 2007

Many patients with type 2 diabetes are denied treatment with metformin because of “contraindications” such as cardiac failure, which may not be absolute contraindications

Summary points

  • Treatment with metformin is not associated with an increased risk of lactic acidosis among patients with type 2 diabetes mellitus who have no cardiac, renal, or liver failure

  • Despite increasing disregard of contraindications to metformin by physicians, the incidence of lactic acidosis has not increased, so metformin may be safe even in patients with “contraindications”

  • The vast majority of case reports relating metformin to lactic acidosis report at least one other disease/illness that could result in lactic acidosis

  • Use of metformin in patients with heart failure might be associated with lower mortality and morbidity, with no increase in hospital admissions and no documented increased risk of lactic acidosis

  • Further studies are needed to assess the risk of lactic acidosis in patients with type 2 diabetes and traditional contraindications to metformin

Metformin first became available in the United Kingdom in 1957 but was first prescribed in the United States only in 1995.w1 The mechanism of action has been extensively reviewed.w2 w3 The UK prospective diabetes study showed that metformin was associated with a lower mortality from cardiovascular disease than sulphonylureas or insulin in obese patients with type 2 diabetes mellitus.1 It was also associated with reduced all cause mortality, which was not seen in patients with equally well controlled blood glucose treated with sulphonylureas or insulin.1

Despite the evidence base for the benefits of metformin, concerns remain about its side effects and especially the perceived risk of lactic acidosis in the presence of renal, hepatic, respiratory, or cardiac failure.2w4 w5 Perhaps as a result of this, many suitable patients with type 2 diabetes are denied metformin treatment.3w6 w7 The …

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