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Loop Diuretic

Furosemide 40–500mg oral / 20–200mg IV

Brand names: Lasix, Frusol (oral solution)

Adult dose

Dose: Oral: 40–80mg OD (standard); up to 500mg/day in severe CKD/resistant oedema. IV: 20–40mg initially; up to 200mg IV for severe oedema in CKD/dialysis.
Route: Oral or IV
Frequency: Once daily (OD) or twice daily (BD) for oedema; IV as required
Max: 500mg/day oral; 200mg per IV bolus (give slowly >4 min to avoid ototoxicity)
Escalating doses required in CKD — reduced tubular secretion means higher doses needed for equivalent effect. IV rate: do not exceed 4mg/min (ototoxicity). Continuous IV infusion (5–10mg/h) may be more effective than bolus in resistant oedema.

Paediatric dose

Dose: 1 mg/kg
Route: Oral or IV
Frequency: OD–BD
Max: 6 mg/kg/day (max 40mg/dose neonates; 80mg/dose children)
Concentration: 10 mg/mL oral solution; 10 mg/mL IV mg/ml
Neonates: 0.5–1 mg/kg per dose every 12–24h (avoid prolonged use — nephrocalcinosis risk). Children: 1–2 mg/kg per dose OD–BD (max 40mg). IV: over at least 15 min in children.

Dose adjustments

Renal

Higher doses required as eGFR falls — CKD stage 5/dialysis: 80–250mg OD oral, or IV; monitor response. IV preferred in severe oedema with poor GI absorption.

Hepatic

Caution in severe hepatic impairment — hyponatraemia and hypokalaemia can precipitate hepatic encephalopathy; start low and titrate

Paediatric weight-based calculator

Neonates: 0.5–1 mg/kg per dose every 12–24h (avoid prolonged use — nephrocalcinosis risk). Children: 1–2 mg/kg per dose OD–BD (max 40mg). IV: over at least 15 min in children.

Clinical pearls

  • Dose escalation in CKD is necessary — as eGFR falls, furosemide delivery to tubule is reduced (protein-bound; secreted by organic anion transporters); 2–4× dose escalation common in CKD stage 4–5
  • IV furosemide in fluid-overloaded dialysis patient: often needed even on dialysis for intradialytic fluid removal; 250mg IV over 30 min is appropriate in anuric/oliguric patients before considering ultrafiltration
  • Continuous IV infusion (5–10 mg/h): more effective than intermittent boluses in resistant oedema — reduces peak drug levels and associated ototoxicity
  • Triple whammy: ACEi + diuretic + NSAID = high-risk combination for AKI — commonest preventable cause of AKI in UK
  • Metolazone combination for diuretic resistance: add metolazone 2.5–5mg OD to loop diuretic for sequential nephron blockade

Contraindications

  • Anuria (unless in oliguric AKI — trial dose acceptable)
  • Hypovolaemia/severe dehydration
  • Severe hypokalaemia or hyponatraemia
  • Hypersensitivity to sulfonamides (cross-reactivity)

Side effects

  • Hypokalaemia (most common — supplement or add potassium-sparing diuretic)
  • Hyponatraemia
  • Dehydration and AKI (over-diuresis)
  • Ototoxicity (high-dose IV — administer slowly)
  • Hyperuricaemia/gout
  • Hyperglycaemia
  • Metabolic alkalosis

Interactions

  • ACEi/ARBs — first-dose hypotension and AKI (triple whammy with NSAIDs)
  • Aminoglycosides — additive ototoxicity and nephrotoxicity
  • NSAIDs — reduce diuretic effect and increase AKI risk
  • Lithium — furosemide increases lithium toxicity
  • Digoxin — hypokalaemia increases toxicity

Monitoring

  • Serum electrolytes (Na+, K+, Mg2+) — daily in acute setting
  • Renal function (creatinine, urea)
  • Blood pressure (postural hypotension)
  • Fluid balance and daily weight
  • Uric acid (long-term)

Reference: BNFc; BNF; ESC Heart Failure Guidelines 2021; NICE NG203; KDIGO AKI Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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