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Biguanide

Metformin hydrochloride

Brand names: Glucophage, Metformin SR

Adult dose

Dose: 500mg OD with food; titrate weekly to 500–1000mg BD–TDS (max 3g/day in divided doses or 2g/day MR)
Route: PO
Frequency: OD-TDS

Dose adjustments

Renal

eGFR 30–45: max 1g/day, monitor; eGFR <30 avoid (MHRA 2016)

Clinical pearls

  • First-line for type 2 DM (NICE NG28); useful in PCOS
  • MR formulations improve GI tolerance

Contraindications

  • eGFR <30
  • DKA
  • Severe hepatic impairment
  • Acute heart failure / hypoxia / sepsis
  • Concurrent IV iodinated contrast (hold around procedure if eGFR <60)

Side effects

  • GI upset (very common — start low, titrate)
  • Lactic acidosis (rare, at-risk patients)
  • Vitamin B12 deficiency (long-term, MHRA warning)
  • Metallic taste

Interactions

  • Iodinated contrast (hold)
  • Alcohol
  • Cimetidine (raised levels)
  • ACE inhibitors / NSAIDs (renal)

Monitoring

  • HbA1c
  • Renal function
  • Vitamin B12 (yearly long-term)

Reference: BNF; NICE NG28; MHRA Drug Safety Update; https://bnf.nice.org.uk/drugs/metformin-hydrochloride/. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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