• Class of oral diabetes drugs
  • Work by decreasing liver glucose production and increasing insulin sensitivity (Rena et al., 2017)
  • Metformin is the most commonly prescribed biguanide
    • First-line treatment for type 2 diabetes
    • Helps lower blood glucose levels by decreasing hepatic glucose production and increasing peripheral glucose uptake (Rena et al., 2017)
    • Also helps lower LDL cholesterol and triglyceride levels (Aroda et al., 2016)
    • Generally, well tolerated but common side effects include diarrhea, nausea, vomiting, flatulence
    • Contraindicated in patients with impaired renal function due to risk of lactic acidosis (Rena et al., 2017)
    • Dosage needs to be adjusted based on renal function
    • Available as immediate release (taken 2-3 times per day) or extended release (once or twice daily) formulations
  • Mechanism of action
    • Activates AMP-activated protein kinase (AMPK) (Rena et al., 2017)
      • Key regulator of lipid and glucose metabolism
      • Activation of AMPK inhibits gluconeogenesis in liver
      • Also increases glucose uptake in muscles
    • May also inhibit mitochondrial glycerophosphate dehydrogenase (Rena et al., 2017)
      • Lowers conversion of lactate to pyruvate
      • Reduces gluconeogenesis
  • Advantages
    • Long history of use, low cost
    • Good efficacy in lowering A1c
    • Low risk of hypoglycemia
    • Potential cardioprotective effects
  • Disadvantages
    • GI side effects common
    • Contraindicated in renal impairment
    • Vitamin B12 deficiency risk (Aroda et al., 2016)
    • Slow onset of action – may take weeks to see full glucose lowering effect
  • Place in therapy
    • Recommended as first line treatment in most patients with type 2 diabetes
    • Should be used with lifestyle modification (diet, exercise)
    • Often used in combination with other agents when monotherapy insufficient over time.

In summary, biguanides such as metformin are commonly used oral medications for type 2 diabetes that reduce hepatic glucose production and increase insulin sensitivity. Metformin is usually the first line drug, has a good efficacy and safety profile, but is contraindicated in renal impairment. It is often combined with other agents when needed to improve glucose control.


Aroda, V.R., Edelstein, S.L., Goldberg, R.B., Knowler, W.C., Marcovina, S.M., Orchard, T.J., Bray, G.A., Schade, D.S., Temprosa, M.G., White, N.H. and Crandall, J.P., 2016. Long-term metformin use and vitamin B12 deficiency in the diabetes prevention program outcomes study adult cohort. The Journal of Clinical Endocrinology & Metabolism, 101(4), pp.1754-1761.

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Bailey, C.J. and Day, C., 1989. Metformin: its botanical background. Practical Diabetes, 6(3), pp.115-117.

Rena, G., Hardie, D.G. and Pearson, E.R., 2017. The mechanisms of action of metformin. Diabetologia, 60(9), pp.1577-1585.