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Loop diuretic Pregnancy: Use only if clearly indicated. Reduces placental perfusion; may impair fetal renal development.

Furosemide (Frusemide)

Brand names: Lasix, Frusol

Adult dose

Dose: Oedema/Heart failure: 20–80 mg once daily; Acute pulmonary oedema: 40–80 mg IV
Route: Oral or IV
Frequency: Once or twice daily oral; single dose IV (acute)
Max: 1 g/day (rarely needed); acute: 80 mg IV in first instance
HF oedema: start 40 mg OD (oral), up to 80–120 mg/day in divided doses. Acute pulmonary oedema: 40–80 mg IV (inject over 2 min if >4 mg/min — ototoxicity risk). Give in morning or morning + noon (avoid evening — nocturia).

Paediatric dose

Dose: 1 mg/kg
Route: Oral or IV
Frequency: Once or twice daily
Max: 6 mg/kg/day
Concentration: 10 mg/ml
Neonates: 0.5–2 mg/kg every 12–24 hours. 1 month–17 years: 0.5–2 mg/kg every 6–12 hours (max 12 mg/kg/day). Note: in premature neonates, furosemide may increase risk of nephrocalcinosis — specialist guidance.

Dose adjustments

Renal

Higher doses often required in renal impairment (tubular secretion reduced). Can use up to 250–500 mg doses IV in severe renal failure under specialist supervision.

Hepatic

Use with caution; hypokalaemia may precipitate hepatic encephalopathy.

Paediatric weight-based calculator

Neonates: 0.5–2 mg/kg every 12–24 hours. 1 month–17 years: 0.5–2 mg/kg every 6–12 hours (max 12 mg/kg/day). Note: in premature neonates, furosemide may increase risk of nephrocalcinosis — specialist guidance.

Clinical pearls

  • Start ACE inhibitors/ARBs at low dose and hold diuretics for 24–48 hours to avoid first-dose hypotension
  • Potassium monitoring essential — hypokalaemia increases digoxin toxicity
  • Elderly: risk of falls with hypotension and nocturia — review dose regularly
  • IV ototoxicity: do not exceed 4 mg/min IV infusion rate
  • Resistance to oral furosemide in decompensated HF: switch to IV then revert to oral once improved

Contraindications

  • Anuria unresponsive to furosemide
  • Severe hypokalaemia or hyponatraemia
  • Dehydration

Side effects

  • Hypokalaemia (most common — supplement or co-prescribe potassium-sparing agent)
  • Hyponatraemia
  • Dehydration and hypotension
  • Metabolic alkalosis
  • Ototoxicity (rapid IV administration or high doses)
  • Hyperuricaemia and gout
  • Impaired glucose tolerance

Interactions

  • ACE inhibitors/ARBs — first-dose hypotension; stop furosemide for 48 hours before starting
  • NSAIDs — reduced diuretic efficacy; increased AKI risk ('triple whammy')
  • Aminoglycosides — additive ototoxicity
  • Digoxin — hypokalaemia increases digoxin toxicity
  • Lithium — increased lithium toxicity (increased reabsorption in hypovolaemia)

Monitoring

  • U&E (potassium, sodium, creatinine) — check 48–72h after any dose change
  • Weight (daily in HF)
  • BP
  • Fluid balance

Reference: BNFc; BNF; NICE NG106 Heart Failure; ESC HF Guidelines 2021; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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