Metformin
also: biguanide · first-line T2DM
Overview
First-line drug for type 2 diabetes — weight-neutral, no hypoglycaemia as monotherapy, cardiovascular benefit. Also used in PCOS.
Mechanism
Activates AMP-activated protein kinase (AMPK) → reduces hepatic gluconeogenesis (main effect), increases peripheral insulin sensitivity and glucose uptake, and reduces intestinal glucose absorption. Does NOT stimulate insulin secretion → no hypoglycaemia alone.
Indications
- Type 2 diabetes (first-line)
- PCOS (off-label, insulin resistance)
Adverse effects
Commonest; modified-release improves tolerance.
Rare; risk ↑ in renal impairment, sepsis, hypoxia, contrast.
Long-term; check B12 if neuropathy/anaemia.
Cautions & contraindications
Lactic acidosis risk — stop; review dose at <45.
AKI → accumulation.
Interactions
- Nephrotoxins/contrast → lactic acidosis risk
- Alcohol excess
Monitoring & kinetics
Renal function (≥annual),B12 if symptomatic
Oral with food. Renally cleared — the eGFR thresholds are the key safety rule.
Choosing it
true
Source: NICE NG28 — Type 2 diabetes · BNF — Metformin