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Loop Diuretic Pregnancy: Teratogenic and embryotoxic potential in humans is unknown; should not be used in pregnancy unless benefits outweigh possible risk to the foetus (which includes persistence of patent ductus arteriosus). May pass into breast milk or inhibit lactation — use with caution in nursing mothers (contraindicated in breast-feeding women per section 4.3).

Furosemide

Brand names: Lasix

Furosemide is a loop diuretic used to treat fluid overload in heart failure, renal disease, hepatic cirrhosis and resistant hypertension.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Oedema: initially 40 mg in the morning (maintenance 20 mg daily or 40 mg on alternate days)
Route: oral
Frequency: once daily (morning), adjusted to response
Max: Resistant oedema up to 80 mg daily; chronic renal insufficiency up to 1,500 mg/24 h (exceptionally up to 2,000 mg/24 h)
General medicine variant. Adults and children over 12 years. Oedema: initially 40 mg daily in the morning; maintenance 20 mg daily or 40 mg on alternate days, increased in resistant oedema to 80 mg daily. Hypertension: 20–40 mg twice daily; if 40 mg twice daily is inadequate, add other antihypertensives rather than increase the furosemide dose. Chronic renal insufficiency: initial daily dose 250 mg, increased in steps of 250 mg at 4–6 hourly intervals up to a maximum 1,500 mg/24 h (exceptionally up to 2,000 mg/24 h). Elderly: eliminated more slowly — titrate to response. Children under 12 years (per SPC): 1–3 mg/kg body weight daily, max total 40 mg/day — verify paediatric dosing against a children's formulary.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to furosemide, any excipient, sulphonamides or sulphonamide derivatives/amiloride
  • Anuria and impaired renal function (creatinine clearance below 30 mL/min per 1.73 m2) and renal failure from nephrotoxic/hepatotoxic poisoning
  • Severe hypokalaemia, severe hyponatraemia, hypovolaemia, dehydration and/or hypotension
  • Concomitant potassium supplements or potassium-sparing diuretics
  • Pre-coma/coma associated with hepatic cirrhosis or encephalopathy
  • Addison's disease
  • Digitalis intoxication
  • Breast-feeding women

Side effects

  • Thrombocytopenia (uncommon)
  • Cardiac arrhythmias (uncommon); reduction in blood pressure
  • Deafness (sometimes irreversible), tinnitus (uncommon/rare)
  • Dry mouth, nausea, vomiting, diarrhoea, constipation (uncommon)
  • Electrolyte and water disturbance (hypokalaemia, hyponatraemia, hypocalcaemia, hypomagnesaemia); metabolic acidosis

Interactions

  • ACE inhibitors / angiotensin II receptor blockers — marked falls in blood pressure and possible impaired renal function; stop or reduce furosemide before starting an ACE inhibitor
  • Antihypertensives — enhanced hypotensive effect
  • Post-synaptic alpha blockers (e.g. prazosin) — risk of first-dose hypotensive effect
  • Antipsychotics — furosemide-induced hypokalaemia increases risk of cardiac toxicity; avoid pimozide; increased ventricular arrhythmia risk with amisulpride
  • Colestyramine and colestipol — administer 2 to 3 hours apart

Clinical monograph

How it works

It inhibits the sodium-potassium-chloride co-transporter in the thick ascending limb of the loop of Henle, producing potent natriuresis and diuresis.

Prescribing in practice

  • It can cause electrolyte disturbance, most notably hypokalaemia, along with hyponatraemia, hypomagnesaemia and dehydration with prerenal kidney injury.
  • Ototoxicity may occur, particularly with rapid intravenous administration, high doses or co-administration with other ototoxic drugs such as aminoglycosides.
  • It can precipitate or worsen gout and may unmask urinary retention in men with prostatic enlargement.

Monitoring

Monitor renal function, electrolytes and fluid status, particularly on initiation, dose changes and during intercurrent illness.

Counselling the patient

  • Take in the morning to avoid disturbed sleep from passing urine at night.
  • Report muscle cramps, dizziness, marked thirst or confusion, which may signal salt or water imbalance.
  • Weigh yourself regularly if advised, to help track fluid balance.

Evidence & guidelines

Furosemide is the standard loop diuretic in NICE heart failure and chronic kidney disease guidance for symptomatic relief of congestion.

Reference: NICE NG106 (Chronic Heart Failure); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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