Lasix (furosemide)

Pronunciation: fyoor-OH-se-mide.

Generic name
furosemide (also called frusemide in some countries)
Drug class
Loop diuretic
Form
Tablet, oral solution, and injection (strengths vary by country and product, commonly 20 mg, 40 mg, and 80 mg tablets, and 10 mg/mL injection)
Route
Oral or intravenous/intramuscular injection
Legal status
Prescription-only in all markets reviewed

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Lasix (5) · Full directory

What furosemide (also called frusemide in some countries) is and how it works

Lasix (furosemide) is a prescription loop diuretic ('water pill') that helps the kidneys remove excess salt and water from the body by increasing urine production. It is used for fluid build-up (oedema) caused by conditions such as heart failure, liver disease, or kidney disease, and for high blood pressure. (1)

Furosemide carries a genuine safety warning: because it is such an effective diuretic, taking too much, or not being monitored closely enough, can lead to dehydration and dangerously low levels of body salts (electrolytes) such as sodium and potassium. This is why careful, individualised dosing and regular blood tests are part of safe treatment with this medicine.

Mechanism of action: how furosemide (also called frusemide in some countries) works

Furosemide is a loop diuretic that inhibits the Na+/K+/2Cl- cotransporter in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium, chloride, and potassium and producing a potent diuresis. This is the basis for its use in oedema and (via reduced circulating volume) hypertension. (1) (2) (4)

What furosemide (also called frusemide in some countries) is used for

Fluid retention (oedema) from heart failure, liver disease, or kidney disease

Used to reduce swelling and fluid build-up caused by congestive heart failure, cirrhosis of the liver, and kidney disease including nephrotic syndrome. In some markets, it is also used by injection for acute pulmonary oedema (fluid in the lungs) and, less commonly, cerebral oedema, when rapid fluid removal is needed or oral medicine is not practical. (1) (6)

High blood pressure (hypertension)

Used in adults for high blood pressure, either alone or combined with other blood-pressure-lowering medicines. (1) (2) (6)

Before taking furosemide (also called frusemide in some countries)

Do not take / not appropriate for

  • Do not take furosemide if you have a known serious allergic reaction to furosemide. (all countries) (1)
  • Do not take furosemide if you are producing no urine at all (anuria). (all countries) (1)
  • Do not take furosemide if you have a known allergy to sulfonamide medicines (such as certain antibiotics or sulfonylurea diabetes medicines) -- cross-sensitivity is possible; confirmed as a contraindication-level concern in the UK and Canadian sources reviewed. (United Kingdom, Canada) (2) (4)
  • Do not take furosemide if you have severe dehydration, severely low blood sodium or potassium, very low blood pressure, complete kidney shutdown, or hepatic coma/pre-coma -- these conditions must be corrected first, per the UK and Canadian sources reviewed. (United Kingdom, Canada, New Zealand) (2) (4)
  • Do not breastfeed while taking furosemide -- stated as a contraindication in the UK and Canadian sources reviewed (the US source describes this as requiring caution rather than an absolute prohibition). (United Kingdom, Canada) (2) (4)

Tell your clinician about

  • Any history of kidney or liver problems, including cirrhosis.
  • Any history of gout, diabetes, or hearing problems.
  • Any allergy to sulfonamide medicines.
  • All other medicines, especially other diuretics, aminoglycoside antibiotics, lithium, NSAIDs, digoxin, or ACE inhibitors/ARBs.
  • Whether you are pregnant, plan to become pregnant, or are breastfeeding.
(1) (2) (4)

How to take furosemide (also called frusemide in some countries)

  • Usually taken in the morning (or with an additional afternoon dose for twice-daily regimens), since it increases urination.
  • Your prescriber will set a dose and schedule that suits your specific condition and response -- both the dose and the interval between doses matter for staying safe on this medicine.
  • Regular blood tests to check kidney function and electrolyte (salt) levels are a normal part of monitoring while on this medicine.
  • Any change in dose, or a decision to stop furosemide, should always be made together with your prescriber, not on your own.
(1) (2) (4) (6)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

If you miss a dose, contact your prescriber or pharmacist for guidance, especially if it is close to your next scheduled dose. Because this medicine increases urination, your prescriber may advise avoiding a dose close to bedtime -- follow their specific instructions for your situation.

Overdose

Seek urgent medical attention if you think too much furosemide has been taken, or if you notice severe dizziness, fainting, a very fast or irregular heartbeat, severe thirst, confusion, or reduced urination. Take the medicine packaging with you if possible; there is no specific antidote, and treatment is supportive. (4)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Increased urination, especially soon after taking a dose.

What to notice: Increased urination, especially soon after taking a dose.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Low blood pressure, dizziness, or light-headedness (especially on standing up).

What to notice: Low blood pressure, dizziness, or light-headedness (especially on standing up).

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Dehydration and low blood sodium, potassium, magnesium, or calcium levels.

What to notice: Dehydration and low blood sodium, potassium, magnesium, or calcium levels.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Raised blood urea or creatinine levels.

What to notice: Raised blood urea or creatinine levels.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Muscle cramps.

What to notice: Muscle cramps.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Nausea, vomiting, or gastrointestinal upset.

What to notice: Nausea, vomiting, or gastrointestinal upset.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Signs of dehydration or electrolyte imbalance — boxed_warning

Symptoms: Dry mouth, unusual thirst, weakness, drowsiness, restlessness, muscle pain or cramps, a fast or irregular heartbeat, very low urine output, or nausea and vomiting.

Action: Contact your clinician promptly for assessment and blood tests -- excessive diuresis with water and electrolyte depletion is furosemide's boxed-warning risk, and careful, individualised dosing and monitoring are needed to prevent it. (1) (4)

Signs of hearing changes (ototoxicity) — high caution

Symptoms: Ringing in the ears (tinnitus), or new hearing loss or muffled hearing.

Action: Contact your clinician promptly -- this risk is higher with rapid intravenous injection, high doses, severe kidney impairment, or when combined with certain other medicines (such as aminoglycoside antibiotics). (1) (2)

Signs of a serious allergic or severe skin reaction — emergency

Symptoms: Swelling of the face, lips, tongue, or throat; difficulty breathing; widespread rash, blistering, or peeling skin.

Action: Seek emergency medical help immediately. (2)

Signs of a very low blood cell count (rare) — high caution

Symptoms: Unusual bruising or bleeding, frequent infections, or severe tiredness.

Action: Contact your clinician for assessment and blood tests -- very rare blood disorders (such as aplastic anaemia or agranulocytosis) have been reported. (2)

Interactions

  • Aminoglycoside antibiotics (such as gentamicin): combined use increases the risk of hearing damage (ototoxicity) and is generally avoided except in life-threatening situations. (1) (2)
  • Lithium: furosemide can reduce how quickly the body clears lithium, raising the risk of lithium toxicity; this combination is generally avoided or requires close monitoring. (1) (2)
  • NSAIDs (such as ibuprofen): may reduce furosemide's diuretic and blood-pressure-lowering effect, and combined use can increase the risk of kidney problems. (1) (2)
  • Digoxin: low potassium from furosemide can make digoxin's effects on the heart more dangerous; monitoring of potassium levels is important. (1)
  • ACE inhibitors and ARBs (blood pressure medicines): combining with furosemide can cause a significant drop in blood pressure, especially with the first dose, and may affect kidney function. (1) (2)
  • Potassium supplements or potassium-sparing diuretics: combining with furosemide needs your clinician's assessment, and is contraindicated without demonstrated need in the UK source reviewed. (2)
  • Vancomycin: increased risk of ototoxicity when combined with furosemide. (2)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Furosemide crosses the placenta. It is used in pregnancy only if your prescriber judges the potential benefit clearly justifies the risk, per the US source reviewed, and the UK source reviewed similarly limits use to compelling medical reasons. (1) (2) (3) (4) (5) (6)

Breastfeeding

Furosemide passes into breast milk and may reduce milk supply. The UK and Canadian sources reviewed describe breastfeeding as contraindicated during treatment; the US source reviewed advises caution. Discuss feeding options with your prescriber. (1) (2) (3) (4) (5) (6)

Children

Used in infants and children for oedema, with weight-based dosing set by a specialist and usually started in hospital with close monitoring of electrolytes; a lower dose ceiling applies in newborns and premature infants, per the sources reviewed. (1) (2) (3) (4) (5) (6)

Elderly

No specific dose adjustment based on age alone is described in the sources reviewed, but older adults may be more susceptible to dehydration, low blood pressure, and electrolyte disturbances, so closer monitoring may be appropriate. (1) (2) (3) (4) (5) (6)

Hepatic_impairment

Used with particular caution in liver disease (such as cirrhosis) -- electrolyte disturbances can precipitate hepatic coma, and furosemide is contraindicated in hepatic coma or pre-coma until the underlying condition is corrected, per the UK and Canadian sources reviewed. (1) (2) (3) (4) (5) (6)

Renal_impairment

Elimination is slower and the half-life prolonged in kidney impairment, per the UK source reviewed; furosemide is contraindicated in complete kidney shutdown (anuria) and dosing needs individualised adjustment in significant renal impairment. (1) (2) (3) (4) (5) (6)

Source_ids

US-DAILYMED-LASIX-2026,UK-EMC-FUROSEMIDE-2026,CA-HC-LASIX-PM-2026 (1) (2) (3) (4) (5) (6)

Monitoring

Before starting

  • Baseline kidney function and electrolytes (sodium, potassium, magnesium, calcium)
  • Baseline blood pressure and fluid status
  • Review of other medicines for interactions (aminoglycosides, lithium, NSAIDs, digoxin, ACE inhibitors/ARBs)

During treatment

  • Regular blood tests for electrolytes and kidney function, especially with higher doses or prolonged use.
  • Monitoring for signs of dehydration, low blood pressure, or electrolyte imbalance (weakness, muscle cramps, confusion, irregular heartbeat).
  • Monitoring for hearing changes, particularly if other ototoxic medicines are used concurrently or with high-dose/rapid intravenous administration.
  • Blood glucose monitoring, since furosemide can raise blood sugar levels.
(1) (4)

Storage

Store at room temperature, protected from light and moisture, out of reach of children.

Study the drug class: Loop diuretics

Professional information

Clinician-facing context only, sourced from the current US FDA prescribing information, UK emc SmPC, and Health Canada product monograph reviewed for this dossier; verify against the current full label before prescribing.

United States

Indication: Oedema, hypertension

Dose summary: Oedema: 20-80 mg initial, titrate in 20-40 mg steps, max 600 mg/day for severe cases. Hypertension: ~80 mg/day (often 40 mg twice daily). Paediatric: 2 mg/kg initial, titrate 1-2 mg/kg, max 6 mg/kg/day not recommended.

Renal context: Contraindicated in anuria; caution and monitoring needed in renal impairment. (1)

United Kingdom

Indication: Oedema, hypertension

Dose summary: Oedema: 40 mg initial (morning), maintenance 20 mg daily or 40 mg alternate days, resistant cases up to ~80 mg/day. Hypertension: 20-40 mg twice daily, add another agent rather than escalate further.

Renal context: Contraindicated in severe renal impairment (CrCl <30 mL/min/1.73m2); elimination slower and half-life prolonged in renal insufficiency. (2)

Canada

Indication: Oedema, hypertension

Dose summary: Oedema: 40-80 mg initial, titrate in 20-40 mg steps, max 200 mg/day; careful monitoring above 120 mg/day. Hypertension: 20-40 mg twice daily. Paediatric: 0.5-1.0 mg/kg initial, max 2 mg/kg/day (1 mg/kg/day in newborns/premature infants).

Renal context: Contraindicated in complete renal shutdown; individualised adjustment needed in renal impairment. (4)

New Zealand

Indication: Oedema, hypertension, acute pulmonary/cerebral oedema (injection)

Dose summary: Oedema: 20-80 mg initial, titrate in 20-40 mg steps no sooner than 6-8 hours apart, up to 400 mg/day (except advanced renal failure) in severe cases.

Renal context: Dose ceiling of 400 mg/day does not apply in advanced renal failure -- individualised prescriber judgement required. (6)

Mechanism of action

Hepatic guidance

Contraindicated in hepatic coma/pre-coma until the underlying condition is corrected, since electrolyte disturbance can precipitate hepatic coma in cirrhotic patients.

Overdose note

No specific antidote; manage with fluid and electrolyte replacement, supportive care, and monitoring for cardiac arrhythmia; contact a poison control centre for guidance. (1) (2) (4)

Frequently asked questions

Is Lasix (furosemide) available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes. Furosemide is authorised and marketed in all six regions -- as Lasix in the US, UK (also as generic furosemide), Canada, Australia, and New Zealand, and as Lasix or Lasilix nationally across European Union member states, alongside many generics. (1) (2) (3) (4) (5) (6)

Why does Lasix have a boxed warning?

Because it is such a potent diuretic that, given in excessive amounts without proper monitoring, it can cause profound water and electrolyte loss (dehydration and dangerously low sodium, potassium, magnesium, or calcium levels). This is a real safety warning about the importance of individualised dosing and medical supervision -- it is not a warning about a specific organ injury like some other boxed-warning medicines. (1)

Is the maximum dose of Lasix the same everywhere?

No -- this is a genuine difference between the sources reviewed. The US source describes a ceiling of 600 mg/day for severe, refractory oedema, the New Zealand source describes 400 mg/day, and the Canadian source describes 200 mg/day, while the UK source describes typical use up to about 80 mg/day. Always follow your own prescriber's dosing instructions rather than assuming a figure from another country applies to you. (1) (6) (4) (2)

What is the mechanism of action of furosemide (also called frusemide in some countries)?

Furosemide is a loop diuretic that inhibits the Na+/K+/2Cl- cotransporter in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium, chloride, and potassium and producing a potent diuresis. This is the basis for its use in oedema and (via reduced circulating volume) hypertension. (1) (2) (4)

What is the generic name of Lasix (furosemide)?

The generic name is furosemide (also called frusemide in some countries). (1) (5)

What class of drug is furosemide (also called frusemide in some countries)?

Lasix (furosemide) is classed as: Loop diuretic. (1) (5)

References

  1. LASIX (furosemide) tablet -- full prescribing informationU.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Sanofi-Aventis · United States · dated 2026-01-01 · accessed 2026-07-30 · source 1
  2. Furosemide 40 mg Tablets -- Summary of Product Characteristics (SmPC)electronic medicines compendium (emc), United Kingdom -- Summary of Product Characteristics · United Kingdom · dated 2025-06-01 · accessed 2026-07-30 · source 2
  3. Furosemide: list of nationally authorised medicinal products (PSUSA/00001491/201801)European Medicines Agency (EMA) -- list of nationally authorised medicinal products (periodic safety update single assessment) · European Union · dated 2018-01-01 · accessed 2026-07-30 · source 3
  4. LASIX and LASIX Oral Solution (furosemide) -- Product MonographHealth Canada -- Product Monograph (Sanofi-Aventis Canada, Lasix and Lasix Oral Solution) · Canada · dated 2020-01-01 · accessed 2026-07-30 · source 4
  5. LASIX furosemide (frusemide) 40 mg tablet -- ARTG entry 12406; PBS item 2412YTherapeutic Goods Administration (TGA), Australia -- Australian Register of Therapeutic Goods (ARTG) and PBS · Australia · dated 2026-06-01 · accessed 2026-07-30 · source 5
  6. Lasix and Lasix High Dose -- furosemide (frusemide) -- New Zealand Data SheetMedsafe (New Zealand Medicines and Medical Devices Safety Authority) -- New Zealand Data Sheet · New Zealand · dated 2022-06-20 · accessed 2026-07-30 · source 6

Brand names by country

Single-ingredient furosemide (also called frusemide in some countries) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Lasix80 mg, 20 mg, 40 mg · validus pharmaceuticals llc
  • FUROSCIX80 mg/mL, 8 mg/mL · scpharmaceuticals inc., a wholly owned subsidiary of mannkind corporation
  • LASIX ONYU30 mg/mL · sq innovation, inc.

United Kingdom

  • Furosemide (generic; multiple manufacturers) (2)emc current smpc confirmed · 20 mg, 40 mg tablets, 4 mg/mL, 10 mg/mL oral solution, 10 mg/mL, 20 mg/2 mL injection · Multiple generic manufacturers listed on emc

Canada

  • FUROSEMIDE SPECIAL
  • LASIX
  • LASIX SPECIAL
  • FUROSEMIDE INJ
  • FUROSEMIDE INJECTION SDZ

Australia

  • Lasix (5)tga artg registered confirmed · 40 mg tablets, 20 mg/2 mL, 40 mg/4 mL injection · Sanofi-Aventis Australia Pty Ltd

New Zealand

  • Lasix; Lasix High Dose; Apo-Furosemide; Furosemide-Baxter; Furosemide-AFT (6)medsafe data sheet confirmed · tablet and injection formulations, multiple strengths · Multiple Medsafe-approved suppliers (brand and generic)
View brands in additional countries.

European Union

Lasix; Lasilix (and numerous national generics) (3)

This page provides general reference information about Lasix (furosemide) and is not a substitute for advice from the prescriber managing your treatment. All dosing and treatment decisions, including starting, changing, or stopping this medicine, should be made with your prescriber.

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