Metformin

What is Metformin used for?

Metformin is a biguanide antidiabetic drug that improves blood sugar control in type 2 diabetes mainly by reducing hepatic glucose production, increasing peripheral insulin sensitivity, and decreasing intestinal glucose absorption. It is typically used alongside diet and exercise as a first-line treatment.

How to take Metformin and adjust the dose

Adults typically start at 500mg twice daily or 850mg once daily, taken with meals to reduce GI upset; the dose may be increased by 500mg every 1-2 weeks based on blood sugar response, with a typical maintenance dose of 1500-2000mg/day and a maximum of 2550mg/day. Contraindicated with eGFR below 30 mL/min/1.73m²; not recommended to start therapy at eGFR 30-45 — dose must be assessed and adjusted by a doctor based on renal function. (Confidence: fairly high — general dosing range based on international prescribing references; individual dosing still requires physician adjustment based on renal function and glycemic response)

Metformin side effects

• Common: diarrhoea, nausea/vomiting, bloating/gas, stomach pain, indigestion, metallic taste, fatigue, headache (more common initially or after dose increase)
• More serious: long-term use may lower vitamin B12 levels
• Rare and serious (boxed warning): lactic acidosis — symptoms include muscle pain, difficulty breathing, stomach pain with nausea, hypothermia, low blood pressure; potentially fatal emergency

Who should not take Metformin?

• Contraindicated in severe renal impairment (eGFR below 30)
• Contraindicated in severe hepatic, renal or cardiac failure
• Contraindicated in diabetic ketoacidosis or hyperosmolar state
• Contraindicated in known hypersensitivity to metformin
• Not recommended in children under 10
• Elderly patients with reduced renal function have higher lactic acidosis risk and require close monitoring
• May need to be temporarily stopped around iodinated contrast imaging procedures
• Consult a doctor if pregnant or breastfeeding