Biguanides
Examples
Metformin
Indications
Type 2 Diabetes mellitus.
Polycystic ovarian syndrome (unlicensed)
Contraindications
Contraindication
- General anaesthesia (should be withheld on the day of surgery)
- Intra-venous contrast x-rays (should be withheld for at least 2 days)
- Acute metabolic acidosis
Caution
- Renal impairment (risk of lactic acidosis, review if GFR < 45ml / min / 1.73m2)
Mechanism
Metformin acts by inhibiting gluconeogenesis and glycogenolysis in the liver, and increasing insulin sensitivity in muscle and peripheral tissues (and thereby glucose uptake).
A beneficial effect on lipids is also seen.
Metformin can only be effective when there is some residual function in the pancreatic islet cells.
Administration
Given orally, with food.
Adverse Reactions
- Gastrointestinal upset, particularly diarrhoea, is common especially with high doses. A slow increase in dose may help patient tolerance.
- Hypoglycaemia should not occur.
- Lactic acidosis, particularly in patients with concurrent renal impairment.
Interactions
Excessive alcohol consumption can increase risk of lactic acidosis.
Education
Patients and carers should be educated on the risk factors and symptoms of lactic acidosis and when to seek urgent medical attention.
Pharmacokinetics
Nil of note.
