Biguanide (Antidiabetic) Pregnancy: If clinically needed, the use of metformin can be considered during pregnancy and in the periconceptional phase as an addition or an alternative to insulin; a large amount of data indicates no increased risk of congenital abnormalities or feto/neonatal toxicity. Metformin is excreted into human breast milk and breast-feeding is not recommended during metformin treatment.

Metformin (Elderly)

Brand names: Glucophage

This page covers metformin in older patients; it is a biguanide and first-line oral agent for type 2 diabetes, with renal-function-guided use being the key consideration in this group.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Elderly: because of the potential for decreased renal function, the metformin dosage must be adjusted based on renal function (see renal adjustment). Adults with normal renal function (GFR ≥ 90 mL/min): usual starting dose 500 mg or 850 mg metformin hydrochloride 2 or 3 times daily

Route: Oral

Frequency: Two or three times daily, given during or after meals

Max: 3 g (3000 mg) metformin hydrochloride daily, taken as 3 divided doses, in adults with normal renal function. Lower maxima apply by GFR — see renal adjustment

After 10 to 15 days the dose should be adjusted on the basis of blood glucose measurements; a slow increase of dose may improve gastrointestinal tolerability. If transferring from another oral antidiabetic agent, discontinue the other agent and initiate metformin at the dose indicated. Combination with insulin: metformin is given at the usual starting dose of 500 mg or 850 mg 2 or 3 times daily while the insulin dose is adjusted on the basis of blood glucose measurements. Regular assessment of renal function is necessary in the elderly: a GFR should be assessed before initiation and at least annually thereafter, and every 3-6 months in the elderly and in patients at increased risk of further progression of renal impairment. Metformin should be temporarily discontinued in dehydration (severe diarrhoea or vomiting, fever or reduced fluid intake) and in the presence of conditions that alter renal function. Not recommended in patients with known or suspected mitochondrial diseases (e.g. MELAS, MIDD). In stable chronic heart failure metformin may be used with regular monitoring of cardiac and renal function. The SPC also gives separate paediatric posology for children from 10 years of age and adolescents — verify any paediatric dosing against a children's formulary. Note: eMC §4.5 (interactions) was not captured in this source bundle; the interaction entries below are drawn from §4.3/§4.4.

Dose adjustments

Renal

Total maximum daily dose (to be divided into 2-3 daily doses) by GFR — 60-89 mL/min: 3000 mg (dose reduction may be considered in relation to declining renal function); 45-59 mL/min: 2000 mg (review factors that may increase the risk of lactic acidosis before initiation; the starting dose is at most half of the maximum dose); 30-44 mL/min: 1000 mg; below 30 mL/min: metformin is contraindicated.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Any type of acute metabolic acidosis (such as lactic acidosis, diabetic ketoacidosis)
Diabetic pre-coma
Severe renal failure (GFR < 30 mL/min)
Acute conditions with the potential to alter renal function such as dehydration, severe infection, shock
Disease which may cause tissue hypoxia, such as decompensated heart failure, respiratory failure, recent myocardial infarction, shock
Hepatic insufficiency, acute alcohol intoxication, alcoholism

Side effects

Gastrointestinal disorders — nausea, vomiting, diarrhoea, abdominal pain and loss of appetite (very common, mostly at initiation)
Vitamin B12 decrease/deficiency (common)
Taste disturbance (common)
Lactic acidosis (very rare, but serious)
Liver function test abnormalities or hepatitis, and skin reactions such as erythema, pruritus, urticaria (very rare)

Interactions

Iodinated contrast media — intravascular administration may lead to contrast-induced nephropathy, resulting in metformin accumulation and an increased risk of lactic acidosis; metformin should be discontinued prior to or at the time of the imaging procedure (§4.4)
Medicinal products that can acutely impair renal function (such as antihypertensives, diuretics and NSAIDs) should be initiated with caution in metformin-treated patients (§4.4)
Excessive alcohol intake and concomitant use of medicinal products that may cause lactic acidosis increase the risk of lactic acidosis (§4.3, §4.4)

Clinical monograph

How it works

It reduces hepatic gluconeogenesis and improves peripheral insulin sensitivity and glucose uptake, lowering blood glucose without directly stimulating insulin secretion.

Prescribing in practice

Dosing depends on renal function, which declines with age; reduce or avoid in significant renal impairment because of the risk of lactic acidosis, and apply sick-day rules during acute illness or dehydration.
Withhold around the time of iodinated contrast imaging and major surgery where renal function may deteriorate, then restart once renal function is confirmed stable.
Long-term use can cause vitamin B12 deficiency, which is worth considering in older patients with anaemia or neuropathy.

Monitoring

Monitor renal function before starting and periodically thereafter, along with glycaemic control and, where indicated, vitamin B12 status.

Counselling the patient

Take with food to reduce stomach upset; modified-release forms may help if this is troublesome.
Pause it and seek advice if you become dehydrated or acutely unwell (sick-day rules).
Attend regular blood tests to check kidney function and diabetes control.

Evidence & guidelines

The UK Prospective Diabetes Study established metformin as first-line therapy, and NICE supports renal-function-guided dosing with temporary withholding during acute illness.

Reference: NICE NG28; UKPDS; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways