Metformin does not cause hypoglycaemia. Consider stopping in those with elevated creatinine. Omit 48 h before giving IV radiocontrast.
Only if a patient experiences gastrointestinal side effects with standard-release, consideration may be given to a trial of modified-release metformin.
- Metformin is a biguanide. Improves diabetic control without weight gain
Mode of action
- Decreases glucose production by the liver
- Increases glucose uptake peripherally
- increases the peripheral utilisation of glucose by increasing sensitivity to Insulin (decreases Insulin resistance)
- Oral medication given Metformin 500 - 2000 mg/day e.g. 1 g BD
- In adults with type 2 diabetes, review the dose of metformin if eGFR is below 45 ml/minute/1.73m2:
- Initially 500mg with breakfast for at least 1 week then 500mg with breakfast and evening meal for at least 1 week then 500mg with breakfast, lunch and evening meal; usual maximum 2g daily in divided doses (maximum licensed dose: 3g daily)
Increase dose only when patient has been free of side effects for 1 week.
- Titrate to maximum tolerated dose as symptoms allow, do not wait for glycaemic change before increasing dose.
If GI effects are present, then reduce the dose of metformin to highest dose tolerated
Many patients who have failed to tolerate the usual starting dose of metformin, can be successfully managed if the dose is started at 125mg (quarter of a tablet) daily and titrated very slowly.
- Main use is Type 2 Diabetes mellitus especially if obese
- Polycystic Ovarian Syndrome (PCOS)
- Possibly useful in NASH and with Insulin in poorly controlled Type 2 DM
- Used with Sulphonylurea in Type 2 DM
- Both Insulin and metformin are complementary in Type 2 Diabetes and can be used together
- Severe cardiac failure, Liver failure
- Recent Myocardial infarction
- Severe dehydration
- Renal failure Creatinine > 150 umoles/l and Caution if eGFR <45
- Shock, Avoid 48 hours before and after giving IV contrast media
- Avoid in pregnancy or Breastfeeding
- Those with a history of alcohol abuse
- Abdominal bloating, discomfort and nausea and Diarrhoea, B12 deficiency
- Anorexia and Weight loss - which may improve diabetic control
- Lactic acidosis: rare, usually mild but not always. Look for other causes.