ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Biguanide (Antidiabetic) Pregnancy: B

Metformin (Elderly)

Brand names: Glucophage

Adult dose

Dose: 500 mg once or twice daily with meals initially; increase by 500 mg every 1–2 weeks; usual maintenance 1.5–2 g/day
Route: oral
Frequency: two to three times daily (with meals)
Max: 3 g/day
In elderly: cautious use; avoid if eGFR <30 ml/min; reduce dose if eGFR 30–45 ml/min; withhold before contrast media and after surgery

Paediatric dose

Route: oral
Frequency: twice daily
Max: 2 g/day
Concentration: 500 mg/5 mL oral solution mg (flat dose)/ml
Type 2 DM ≥10 years: start 500 mg BD with meals; increase every 2 weeks to max 2 g/day

Dose adjustments

Renal

Reduce to 500–1000 mg/day if eGFR 30–45 ml/min; stop if eGFR <30 ml/min

Hepatic

Avoid in hepatic impairment (lactic acidosis risk)

Clinical pearls

  • No hypoglycaemia as monotherapy — weight neutral or beneficial; reduces CV events (UKPDS)
  • Vitamin B12: check annually in elderly — B12 malabsorption in 10–30% with long-term use
  • STOP before: IV contrast, major surgery, anticipated acute illness — restart when renal function confirmed normal

Contraindications

  • eGFR <30 ml/min
  • Hepatic impairment
  • Excessive alcohol intake
  • Active illness with tissue hypoxia
  • Contrast medium (withhold for 48h)

Side effects

  • GI upset (nausea, diarrhoea)
  • Lactic acidosis (rare but serious, in predisposed patients)
  • Vitamin B12 deficiency (long-term)
  • Metallic taste

Interactions

  • Contrast media (withhold 48h after IV contrast — lactic acidosis risk)
  • Alcohol (lactic acidosis)
  • Cimetidine (increases metformin levels)

Monitoring

  • eGFR every 3–6 months (elderly)
  • Vitamin B12 annually
  • HbA1c every 3–6 months

Reference: BNFc; BNF 86; NICE NG28; UKPDS. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways