Prescribing Notes
- Prescribe as per NICE NG28 recommendations. See also NICE visual summary for blood glucose lowering therapy in adults with type 2 diabetes.
- Metformin may cause gastrointestinal adverse effects; it should be started at low dose and taken with or after meals. A slow increase in dose may improve gastrointestinal tolerability.
- Hypoglycaemia is not a problem with metformin monotherapy.
- For patients with difficulties swallowing tablets, ‘metformin 500mg powder sachets for oral solution’ are a cost-effective option and should be used where possible. Metformin oral solution is very expensive.
Cautions
- Metformin is a useful drug and can be safely used in mild/moderate stable chronic kidney disease (CKD). It is associated with lactic acidosis, however this is rare and the risk may be overstated. Dose reduction and specialist involvement should be considered as renal function declines towards this level. See CKD section in NICE NG28.
- Continuing metformin during periods of dehydration or acute illness (such as diarrhoea or vomiting) can increase the risk of lactic acidosis. This is compounded if the patient is also taking diuretics, ACE inhibitors, ARBs, NSAIDs and/or SGLT-2 inhibitors in combination with metformin. Unlike acute illnesses in type 1 diabetes (where insulin treatment must be continued), stopping the drugs for a day or two will not cause any immediate problem for the patient and will protect renal function until the patient improves. See sick day rules for further information.
- See MHRA, ‘Metformin and reduced vitamin b12 levels: new advice for monitoring patients at risk’.