Metformin (Elderly)

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.