Loop Diuretic Pregnancy: Furosemide crosses the placental barrier and should not be given during pregnancy unless there are compelling medical reasons; it should only be used for pathological causes of oedema not directly or indirectly linked to the pregnancy, and if used, monitoring of fetal growth is required. Diuretic treatment of oedema and hypertension caused by pregnancy is undesirable because placental perfusion can be reduced. Breast-feeding: furosemide is CONTRAINDICATED as it passes into breast milk and may inhibit lactation.

Furosemide (IV — ICU)

Brand names: Lasix

Used in: Heart Failure Chronic Kidney Disease Liver Disease & Cirrhosis Acute Kidney Injury

Furosemide is a loop diuretic used to relieve fluid overload in acute pulmonary oedema and decompensated heart failure, and in other oedematous states; the intravenous route is used when rapid effect or poor gut absorption is a concern.

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: Initially 20 to 50 mg by intramuscular injection or by slow intravenous injection at a rate not exceeding 4 mg/minute

Route: Intramuscular or slow intravenous injection; larger doses as a controlled intravenous infusion

Frequency: Titrated according to the response; with the high-dose (250 mg/25 ml) regimen an effective dose of up to 1,000 mg may be repeated every 24 hours

Max: The rate of administration must never exceed 4 mg/minute. High-dose regimen escalates 250 mg, then 500 mg, then 1,000 mg by infusion — if the third infusion (1,000 mg over 4 hours) is not effective, dialysis will probably be required.

Source quote (eMC §4.2, Furosemide Injection 20mg/2ml and 50mg/5ml): 'Initially, doses of 20 - 50mg may be administered by the intramuscular route, or by slow intravenous injection at a rate not exceeding 4mg/minute. The diuretic effect of furosemide is proportional to the dosage and, if larger doses are required, they should be given as a controlled infusion at a rate not exceeding 4mg/minute and titrated according to the response.' HIGH-DOSE PRODUCT (Furosemide Injection 250mg/25ml, for slow IV administration only): an initial dose of 250 mg (one 25 ml ampoule) may be added to about 225 ml Sodium Chloride Injection BP or Ringer's Solution and infused over one hour at a drip rate of 80 drops/minute (4 mg/minute). If urine output within the next hour is insufficient, 500 mg (two ampoules) in an appropriate infusion fluid may be infused at a rate not exceeding 4 mg/minute; if satisfactory urine output has still not been achieved within one hour of the end of the second infusion, a third dose of 1,000 mg (four ampoules) may be given, again never exceeding 4 mg/minute. In oliguric or anuric patients with significant fluid overload where this method is impracticable, a constant-rate infusion pump with micrometer screw-gauge adjustment may be considered for direct administration into the vein, still never exceeding 4 mg/min. If the response is satisfactory (urine output 40-50 ml/hour), the effective dose (of up to 1,000 mg) may be repeated every 24 hours. ORAL CHANGEOVER: alternatively treatment may be maintained by oral administration using 500 mg by mouth for each 250 mg required by injection, with subsequent adjustment according to response. ELDERLY: elimination of furosemide is generally slower in the elderly; dosage should be titrated until the required effect is achieved. PAEDIATRIC (eMC §4.2, 20mg/2ml and 50mg/5ml): 'Dosages for children range from 0.5 - 1.5mg/kg weight daily up to a maximum total daily dose of 20mg.' For the 250mg/25ml strength the SPC states paediatric dosages must be determined on the basis of the severity of the renal insufficiency and the clinical response to initial doses. A single per-kg figure is not stated, so no structured paediatric dose has been created — verify any paediatric dose against a children's formulary. Furosemide is not recommended in patients at high risk for radiocontrast nephropathy.

Dose adjustments

Renal

Contraindicated in impaired renal function with a creatinine clearance below 30 ml/min per 1.73 m² body surface area, and in anuria or renal failure with anuria not responding to furosemide (eMC §4.3). No graded dose-reduction schedule is stated in the fetched SPC.

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.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Edema Therapy should be individualized according to patient response to gain maximal therapeutic response and to determine the minimal dose needed to maintain that response. Adults: The usual initial dose of furosemide tablets is 20 to 80 mg given as a single dose. Ordinarily a prompt diuresis ensues. If needed, the same dose can be administered 6 to 8 hours later or the dose may be increased. The dose may be raised by 20 or 40 mg and given not sooner than 6 to 8 hours after the previous dose until the desired diuretic effect has been obtained. The individually determined single dose should then be given once or twice daily (e.g., at 8 am and 2 pm). The dose of …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2023-03-01. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Hypersensitivity to the active substance or to any of the excipients; hypersensitivity to amiloride, sulphonamides or sulphonamide derivatives
Hypovolaemia and dehydration (with or without accompanying hypotension)
Severe hypokalaemia; severe hyponatraemia
Comatose or pre-comatose states associated with hepatic cirrhosis
Anuria, or renal failure with anuria not responding to furosemide; renal failure resulting from poisoning by nephrotoxic or hepatotoxic agents; renal failure associated with hepatic coma
Impaired renal function with a creatinine clearance below 30 ml/min per 1.73 m² body surface area
Addison's disease
Digitalis intoxication
Porphyria
Breast-feeding women

Side effects

Symptomatic electrolyte disturbances — hyponatraemia, hypokalaemia, hypocalcaemia, hypomagnesaemia, metabolic alkalosis or acidosis, hypovolaemia and dehydration (frequency not known)
Hypotension (uncommon), and dizziness, syncope and loss of consciousness caused by symptomatic hypotension (not known)
Deafness, sometimes irreversible (uncommon); hearing disorders and tinnitus (rare)
Thrombocytopenia (uncommon); eosinophilia, leukopenia and bone marrow depression (rare); aplastic or haemolytic anaemia and agranulocytosis (very rare)
Cardiac arrhythmias (uncommon); blood creatinine and blood urea increased (uncommon)
Skin and mucous membrane reactions including itching, urticaria, rashes, bullous lesions, erythema multiforme (Stevens-Johnson syndrome and Lyell's syndrome), AGEP and DRESS (rare)

Interactions

NSAIDs — concurrent use should be avoided; if not possible, the diuretic effect of furosemide may be attenuated (eMC §4.4)
ACE inhibitors and angiotensin II receptor antagonists — severe hypotension may occur; the dose of furosemide should be reduced or stopped 3 days before starting or increasing the dose of these agents (eMC §4.4)
Digitalis intoxication — a contraindication to furosemide (eMC §4.3)
Aminoglycoside antibiotics — furosemide may increase ototoxic potential, especially with impaired renal function; avoid this combination except in life-threatening situations (US label)
Ethacrynic acid — should not be used concomitantly because of the possibility of ototoxicity (US label)
Cisplatin — risk of ototoxic effects and enhanced nephrotoxicity if furosemide is not given in lower doses with positive fluid balance (US label)
Lithium — reduced renal clearance and high risk of lithium toxicity (US label)
High-dose salicylates — salicylate toxicity may occur at lower doses because of competitive renal excretory sites (US label)
NOTE: the fetched eMC bundle did not include §4.5, so entries marked 'US label' are from US prescribing information and must be checked against the UK SPC §4.5

Clinical monograph

How it works

Furosemide inhibits the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle, producing a powerful diuresis with loss of sodium, potassium and other electrolytes.

Prescribing in practice

Give intravenous doses slowly; rapid administration of high doses risks ototoxicity, especially in renal impairment.
Monitor fluid balance and electrolytes — hypokalaemia, hyponatraemia and worsening renal function can occur.
Effect may be blunted in significant renal impairment, sometimes needing higher doses or an infusion.

Monitoring

Monitor U&E (sodium, potassium, renal function), fluid balance, weight and blood pressure; watch for over-diuresis.

Counselling the patient

It increases how much you pass urine, so timing of oral doses matters for daily routine.
Report dizziness, cramps, or marked thirst.

Evidence & guidelines

Loop diuretics are first-line for congestion in acute heart failure (NICE NG106); they relieve symptoms but are titrated to clinical response.

Reference: DOSE Trial (Felker et al, NEJM 2011); ESC Heart Failure Guidelines 2021; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Furosemide Stress Test (FST) for AKI Progression · AKI

Drugs

Pathways