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Furosemide
Clinical data
Pronunciation/fjʊˈroʊsəˌmaɪd/
Trade namesLasix, Furoscix, others
AHFS/Drugs.comMonograph
MedlinePlusa682858
License data
Pregnancy
category
  • AU: C
Routes of
administration		Oral (PO), intravenous (IV), intramuscular (IM), subcutaneous (SC)
ATC code
Legal status
Legal status
  • AU: S4 (Prescription only)[1]
  • UK: POM (Prescription only)
  • US: ℞-only[2][3]
  • In general: ℞ (Prescription only)
Pharmacokinetic data
Bioavailability43–69%
Protein binding91–99%
MetabolismLiver and kidney glucuronidation
Onset of actionPOTooltip Oral administration: 30–60 min,
IVTooltip Intravenous therapy: 5 min[4]
Elimination half-lifeup to 100 minutes
ExcretionKidney (66%), bile duct (33%)
Identifiers
  • 4-Chloro-2-[(furan-2-ylmethyl)amino]-5-sulfamoylbenzoic acid
CAS Number
PubChem CID
DrugBank
ChemSpider
UNII
KEGG
ChEBI
ChEMBL
CompTox Dashboard (EPA)
ECHA InfoCard100.000.185 Edit this at Wikidata
Chemical and physical data
FormulaC12H11ClN2O5S
Molar mass330.74 g·mol−1
3D model (JSmol)
  • o1cccc1CNc(cc2Cl)c(C(=O)O)cc2S(=O)(=O)N
  • InChI=1S/C12H11ClN2O5S/c13-9-5-10(15-6-7-2-1-3-20-7)8(12(16)17)4-11(9)21(14,18)19/h1-5,15H,6H2,(H,16,17)(H2,14,18,19) checkY
  • Key:ZZUFCTLCJUWOSV-UHFFFAOYSA-N checkY
  (verify)

Furosemide, sold under the brand name Lasix among others, is a loop diuretic medication used to treat edema due to heart failure, liver scarring, or kidney disease.[4] Furosemide may also be used for the treatment of high blood pressure.[4] It can be taken intravenously or orally.[4] When given intravenously, furosemide typically takes effect within five minutes; when taken orally, it typically metabolizes within an hour.[4]

Common side effects include orthostatic hypotension (decrease in blood pressure while standing, and associated lightheadedness), tinnitus (ringing in the ears), and photosensitivity (sensitivity to light).[4] Potentially serious side effects include electrolyte abnormalities, low blood pressure, and hearing loss.[4] It is recommended that serum electrolytes (especially potassium), serum CO2, creatinine, BUN levels, and liver and kidney functioning be monitored in patients taking furosemide. It is also recommended to be alert for the occurrence of any potential blood dyscrasias.[4]

Furosemide works by decreasing the reabsorption of sodium by the kidneys.[4] Common side effects of furosemide injection include hypokalemia (low potassium level), hypotension (low blood pressure), and dizziness.[5]

Furosemide was patented in 1959 and approved for medical use in 1964.[6] It is on the World Health Organization's List of Essential Medicines.[7] In the United States, it is available as a generic medication.[4] In 2023, it was the 29th most commonly prescribed medication in the United States, with more than 19 million prescriptions.[8][9] In 2020/21 it was the twentieth most prescribed medication in England.[10] It is on the World Anti-Doping Agency's banned drug list due to concerns that it may mask other drugs.[11] It has also been used in race horses for the treatment and prevention of exercise-induced pulmonary hemorrhage.[12][13]

Medical uses

[edit]
Furosemide (Lasix) for injection.

Furosemide is primarily used for the treatment of edema, but also in some cases of hypertension (where there is also kidney or heart impairment).[14] It is often viewed as a first-line agent in most people with edema caused by congestive heart failure because of its anti-vasoconstrictor and diuretic effects.[4][15] Compared with furosemide, however, torasemide (aka "torsemide") has been demonstrated to show improvements to heart failure symptoms, possibly lowering the rates of rehospitalization associated with heart failure, with no difference in risk of death.[16][17][18] Torsemide may also be safer than furosemide.[19][20] Providing self-administered subcutaneous furosemide has been found to reduce hospital admissions in people with heart failure, resulting in significant savings in healthcare costs.[21][22]

Furosemide is also used for liver cirrhosis, kidney impairment, nephrotic syndrome, in adjunct therapy for swelling of the brain or lungs where rapid diuresis is required (IV injection), and in the management of severe hypercalcemia in combination with adequate rehydration.[23]

Kidney disease

[edit]

In chronic kidney diseases with hypoalbuminemia, furosemide is used along with albumin to increase diuresis.[24] It is also used along with albumin in nephrotic syndrome to reduce edema.[25]

Other information

[edit]

Furosemide is mainly excreted by tubular secretion in the kidney. In kidney impairment, clearance is reduced, increasing the risk of adverse effects.[4] Lower initial doses are recommended in older patients (to minimize side effects) and high doses may be needed in kidney failure.[26] It can also cause kidney damage; this is mainly by loss of excessive fluid (i.e., dehydration), and is usually reversible.[citation needed]

Furosemide acts within 1 hour of oral administration (after IV injection, the peak effect is within 30 minutes). Diuresis is usually complete within 6–8 hours of oral administration, but there is significant variation between individuals.[27]

Adverse effects

[edit]

Furosemide also can lead to gout caused by hyperuricemia. Hyperglycemia is also a common side effect.[28][29][30]

The tendency, as for all loop diuretics, to cause low serum potassium concentration (hypokalemia) has given rise to combination products, either with potassium or with the potassium-sparing diuretic amiloride (Co-amilofruse). Other electrolyte abnormalities that can result from furosemide use include hyponatremia, hypochloremia, hypomagnesemia, and hypocalcemia.[31]

In the treatment of heart failure, many studies have shown that the long-term use of furosemide can cause varying degrees of thiamine deficiency, so thiamine supplementation is also suggested.[32]

Furosemide is a known ototoxic agent generally causing transient hearing loss but can be permanent. Reported cases of furosemide-induced hearing loss appeared to be associated with rapid intravenous administration, high dosages, concomitant renal disease, and coadministration with other ototoxic medication.[33][34] However, a recently reported longitudinal study showed that participants treated with loop diuretics over 10 years were 40% more likely to develop hearing loss and 33% more likely of progressive hearing loss compared to participants who did not use loop diuretics.[35] This suggests the long-term consequences of loop diuretics on hearing could be a more significant than previously thought and further research is required in this area.  

Other precautions include nephrotoxicity, sulfonamide (sulfa) allergy, and increased free thyroid hormone effects with large doses.[36]

Interactions

[edit]

Furosemide has potential interactions with these medications:[37]

Potentially hazardous interactions with other drugs:

Mechanism of action

[edit]
Main article: Loop diuretic

Furosemide, like other loop diuretics, acts by inhibiting the luminal Na–K–Cl cotransporter in the thick ascending limb of the loop of Henle, by binding to the Na-K-2Cl transporter, thus causing more sodium, chloride, and potassium to be excreted in the urine.[38]

The action on the distal tubules is independent of any inhibitory effect on carbonic anhydrase or aldosterone; it also abolishes the corticomedullary osmotic gradient and blocks negative, as well as positive, free water clearance. Because of the large NaCl absorptive capacity of the loop of Henle, diuresis is not limited by the development of acidosis, as it is with the carbonic anhydrase inhibitors.[citation needed]

Additionally, furosemide is a noncompetitive subtype-specific blocker of GABA-A receptors.[39][40][41] Furosemide has been reported to reversibly antagonize GABA-evoked currents of α6β2γ2 receptors at μM concentrations, but not α1β2γ2 receptors.[39][41] During development, the α6β2γ2 receptor increases in expression in cerebellar granule neurons, corresponding to increased sensitivity to furosemide.[40]

Pharmacokinetics

[edit]
  • Molecular weight (daltons) 330.7
  • % Bioavailability 47 – 70%
    • Bioavailability with end-stage renal disease 43 – 46%[42][43]
  • % Protein binding 91 – 99[44]
  • Volume of distribution (L/kg) 0.07 – 0.2[45][46]
    • Volume of distribution may be higher in patients with cirrhosis or nephrotic syndrome[45]
  • Excretion
    • % Excreted in urine (% of total dose) 60 – 90[45][46]
    • % Excreted unchanged in urine (% of total dose) 53.1 – 58.8 [47]
    • % Excreted in feces (% of total dose) 7 – 9[27]
    • % Excreted in bile (% of total dose) 6 – 9[46]
  • Approximately 10% is metabolized by the liver in healthy individuals, but this percentage may be greater in individuals with severe kidney failure [46]
  • Renal clearance (mL/min/kg) 2.0[45]
  • Elimination half-life (hrs) 2[44]
    • Prolonged in congestive heart failure (mean 3.4 hrs)[45][48]
    • Prolonged in severe kidney failure (4 – 6 hrs)[49] and anephric patients (1.5 – 9 hrs)[46]
  • Time to peak concentration (hrs)
    • Intravenous administration 0.3[50]
    • Oral solution 0.83[44]
    • Oral tablet 1.45[44]

The pharmacokinetics of furosemide are not significantly altered by food.[51]

No direct relationship has been found between furosemide concentration in the plasma and furosemide efficacy. Efficacy depends upon the concentration of furosemide in urine.[27]

Names

[edit]

Furosemide is the INN and BAN.[52] The previous BAN was frusemide.

Brand names under which furosemide is marketed include Aisemide, Apo-Furosemide, Beronald, Desdemin, Discoid, Diural, Diurapid, Dryptal, Durafurid, Edemid, Errolon, Eutensin, Farsiretic, Flusapex, Frudix, Frusemide, Frusetic, Frusid, Fulsix, Fuluvamide, Furantril, Furesis, Furix, Furo-Puren, Furon, Furosedon, Fusid.frusone, Hydro-rapid, Impugan, Katlex, Lasilix, Lasix, Lodix, Lowpston, Macasirool, Mirfat, Nicorol, Odemase, Oedemex, Profemin, Rosemide, Rusyde, Salix, Seguril, Teva-Furosemide, Trofurit, Uremide, and Urex.

Veterinary uses

[edit]
Furosemide for feline use

The diuretic effects are put to use most commonly in horses to prevent bleeding during a race. In the United States of America, under the racing rules of most states, horses that bleed from the nostrils (exercise-induced pulmonary hemorrhage) three times are permanently barred from racing. Sometime in the early 1970s, furosemide's ability to prevent, or at least greatly reduce, the incidence of bleeding by horses during races was discovered accidentally. Clinical trials followed, and by the decade's end, racing commissions in some states in the USA began legalizing its use on race horses. In 1995, New York became the last state in the United States to approve such use, after years of refusing to consider doing so.[53] Some states allow its use for all racehorses; some allow it only for confirmed "bleeders". Its use for this purpose is still prohibited in many other countries.[citation needed]

Furosemide is also used in horses for pulmonary edema, congestive heart failure (in combination with other drugs), and allergic reactions. Although it increases circulation to the kidneys, it does not help kidney function and is not recommended for kidney disease.[54]

It is also used to treat congestive heart failure (pulmonary edema, pleural effusion, and/or ascites) in cats and dogs.[55]

Horses

[edit]

Furosemide is injected either intramuscularly or intravenously, usually 0.5-1.0 mg/kg twice/day, although less before a horse is raced. As with many diuretics, it can cause dehydration and electrolyte imbalance, including loss of potassium, calcium, sodium, and magnesium. Excessive use of furosemide will most likely lead to a metabolic alkalosis due to hypochloremia and hypokalemia. The drug should, therefore, not be used in horses that are dehydrated or experiencing kidney failure. It should be used with caution in horses with liver problems or electrolyte abnormalities. Overdose may lead to dehydration, change in drinking patterns and urination, seizures, gastrointestinal problems, kidney damage, lethargy, collapse, and coma.

Furosemide should be used with caution when combined with corticosteroids (as this increases the risk of electrolyte imbalance), aminoglycoside antibiotics (increases the risk of kidney or ear damage), and trimethoprim sulfa (causes decreased platelet count). It may also cause interactions with anesthetics, so its use should be related to the veterinarian if the animal is going into surgery, it decreases the kidneys' ability to excrete aspirin, so dosages will need to be adjusted if combined with that drug.

Furosemide may increase the risk of digoxin toxicity due to hypokalemia.

It is recommended that furosemide not be used during pregnancy or in a lactating mare, as it is passed through the placenta and milk in studies with other species. It should not be used in horses with pituitary pars intermedia dysfunction (Equine Cushing's Disease).

Furosemide is detectable in urine 36–72 hours following injection. Its use is restricted by most equestrian organizations.

US major racetracks ban the use of furosemide on race days.[56]

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Furosemide

View on Grokipedia
from Grokipedia
Furosemide is a potent approved by the U.S. (FDA) for the treatment of associated with congestive , hepatic , and renal disease, including , as well as for managing , particularly in patients with advanced . As a member of the class of diuretics, furosemide has been in clinical use for over five decades and is available in various formulations, including oral tablets, oral solutions, intravenous injections, and subcutaneous infusions, allowing for flexible administration based on patient needs and acuity of condition. It is commonly prescribed under the brand name Lasix and works by acting on the kidneys to promote the excretion of excess fluid. Its may prolong in patients with impaired renal function. While effective, furosemide requires careful monitoring due to potential adverse effects, including imbalances such as and , , (especially with rapid intravenous administration), and increased risk of or in susceptible individuals. Contraindications include , to sulfonamides, and severe depletion, and it is typically used alongside dietary modifications and other therapies to optimize outcomes in conditions involving .

Medical uses

Edema

Furosemide is indicated for the treatment of associated with congestive , liver , and renal disease, including the . As a , it promotes to reduce fluid retention and alleviate symptoms of in these conditions. In congestive , furosemide is used to manage pulmonary and systemic by enhancing urinary of sodium and , thereby relieving congestion and improving cardiac function. It is particularly effective in , where intravenous administration rapidly reduces symptoms such as dyspnea and . For liver cirrhosis, furosemide helps alleviate and , often in combination with aldosterone antagonists like to optimize sodium excretion while minimizing loss. This approach addresses the and contributing to fluid accumulation in cirrhotic patients. In renal diseases such as , furosemide counteracts volume overload exacerbated by and , promoting to reduce , though higher doses may be required due to altered in low states. It is frequently combined with infusions to enhance its natriuretic effect in severe cases. Dosing for acute edema management typically begins with an intravenous dose of 20-40 mg, which may be repeated or increased by 20 mg every 2 hours if inadequate response, aiming for a target output of 1-2 liters per day. For chronic , starts at 20-80 mg once daily, titrated based on clinical response, with doses given once or twice daily and a maximum of 600 mg per day in cases. Clinical trials, such as the DOSE study, have shown that furosemide therapy in acute leads to significant symptom relief and decongestion, contributing to shorter hospital stays and reduced readmission rates compared to suboptimal diuretic strategies. Early randomized trials further demonstrated that like furosemide improve clinical outcomes by facilitating earlier discharge in heart failure exacerbations.

Hypertension

Furosemide is employed as a second- or third-line agent in the management of , particularly when first-line therapies such as diuretics, inhibitors, angiotensin receptor blockers, or fail to achieve adequate control. It is often used in combination with inhibitors or beta-blockers to enhance antihypertensive efficacy, especially in patients with volume-dependent or those requiring multiple agents for optimization. This approach leverages furosemide's potent properties to address resistant cases where monotherapy is insufficient. The antihypertensive effect of furosemide primarily stems from , which promotes sodium and water excretion, leading to reduced plasma volume and expansion, thereby lowering . This mechanism is particularly beneficial in associated with fluid retention, though its impact diminishes over time due to compensatory renal adaptations. For oral dosing in hypertension, the typical regimen starts at 40-80 mg daily, often divided into two doses (e.g., 40 mg twice daily), with adjustments based on response and tolerability. Clinical evidence supports its blood pressure-lowering efficacy, as demonstrated in trials showing reductions of approximately 8-10 mm Hg systolic and 5-6 mm Hg diastolic with like furosemide, though long-term cardiovascular outcomes such as risk reduction are more established for thiazide-class diuretics in broader populations. In hypertensive emergencies involving volume expansion, such as flash secondary to , intravenous furosemide is applied to rapidly alleviate fluid overload and improve renal perfusion in the stenotic . This use is targeted at scenarios with acute hemodynamic instability and evidence of volume excess, where it enhances renal blood flow and excretory function without exacerbating stenosis-related issues when administered judiciously. In 2023, furosemide accounted for approximately 19 million prescriptions in the United States, underscoring its ongoing role in managing resistant alongside other agents in clinical practice.

Other uses

Furosemide is employed in the management of severe hypercalcemia, where it promotes urinary calcium to rapidly lower serum calcium levels. This effect occurs through inhibition of sodium and reabsorption in the loop of Henle, which indirectly enhances calcium when combined with saline hydration. In , intravenous furosemide is administered following initial volume repletion to avoid , achieving reductions in serum calcium by facilitating the of 0.7 to 2.7 grams of calcium during . This approach is particularly useful in hypercalcemic crises associated with or . In cases of acute from non-cardiogenic causes, such as (ARDS), furosemide serves an adjunctive role in patients with evidence of . By promoting , it helps mitigate fluid accumulation and improve , with early use linked to reduced hospital mortality in ARDS cohorts exhibiting positive . Animal models of ARDS demonstrate that continuous furosemide infusion enhances intrapulmonary shunt and of non-edematous regions, supporting its cautious application in human patients to manage hydrostatic contributions to edema without exacerbating . Furosemide plays an adjunctive role in treatment by enhancing renal elimination, particularly in patients with adequate kidney function. As a , it increases urinary flow and inhibits in the distal tubule, complementing other therapies like insulin or cation exchangers. This is recommended at doses such as 40 mg intravenously every 12 hours in hypervolemic states, aiding in the shift of serum toward normal levels. An emerging subcutaneous formulation, Furoscix, was approved by the FDA in October 2022 for self-administration in adult patients with New York Heart Association Class II or III to treat congestion due to fluid overload. Delivered via an on-body infusor providing 80 mg over five hours, it achieves intravenous-equivalent at home, reducing emergency room visits and hospitalizations while improving symptom relief and . In 2024, the indication was expanded to include Class IV . In March 2025, the indication was further expanded to include associated with .

Pharmacology

Mechanism of action

Furosemide, a derivative chemically known as 4-chloro-2-[(furan-2-ylmethyl)amino]-5-sulfamoylbenzoic acid, exerts its diuretic effects primarily through of the Na⁺-K⁺-2Cl⁻ (NKCC2), also known as SLC12A1, located on the apical membrane of epithelial cells in the thick ascending limb (TAL) of the . This normally facilitates the coupled of one ion, one ion, and two ions from the tubular lumen into the cell, using the sodium gradient established by the basolateral Na⁺/K⁺-. By binding to NKCC2 with relatively high affinity (IC₅₀ approximately 7 μM in renal models), furosemide prevents this ion influx, disrupting the necessary for paracellular of cations like sodium, calcium, and magnesium in the TAL. The blockade of NKCC2 leads to a marked reduction in the reabsorption of sodium, potassium, and chloride, accounting for up to 25% of filtered sodium under normal conditions, thereby increasing the delivery of isotonic filtrate to the distal convoluted tubule and collecting duct. This excess luminal solute creates an osmotic gradient that impairs water reabsorption in downstream nephron segments, resulting in osmotic diuresis and the excretion of large volumes of dilute urine containing sodium, chloride, potassium, and water. Consequently, this process reduces extracellular fluid volume and plasma osmolality, contributing to furosemide's efficacy in conditions involving fluid overload. Beyond direct tubular effects, furosemide influences renal by increasing renal blood flow through afferent arteriolar and inhibiting , which normally constricts arterioles in response to increased distal sodium delivery. It also stimulates the synthesis of renal prostaglandins, particularly PGE₂, via pathways, enhancing and further potentiating diuresis, though this effect can be attenuated by nonsteroidal anti-inflammatory drugs. These secondary mechanisms amplify the primary NKCC2 inhibition, ensuring robust even in states of reduced renal .

Pharmacokinetics

Furosemide exhibits variable oral ranging from 43% to 69%, primarily due to incomplete absorption and first-pass , while intravenous administration achieves 100% with immediate systemic availability. Following oral dosing, the drug is rapidly absorbed from the , reaching peak plasma concentrations within 1 to 2 hours. In the distribution phase, furosemide is highly bound to plasma proteins, with over 95% binding primarily to , resulting in a small unbound fraction of 2.3% to 4.1% at therapeutic concentrations. The volume of distribution is approximately 0.14 to 0.18 L/kg, indicating limited tissue penetration beyond the vascular compartment. Metabolism of furosemide is limited, occurring mainly in the liver and kidneys to form the furosemide , which retains activity. is predominantly renal, with about 66% of the dose eliminated unchanged in the via active tubular mediated by organic anion transporters (OAT1 and OAT3), while the remaining 33% undergoes biliary and fecal elimination, partly as metabolites. In healthy adults, the elimination ranges from 30 to 120 minutes, but it can prolong significantly, up to 24 hours or more in severe renal impairment due to reduced clearance. Pharmacokinetics can be altered by factors such as , which decreases protein binding and reduces delivery of the drug to the renal site of action, potentially diminishing its diuretic efficacy.

Clinical considerations

Adverse effects

Furosemide, a loop diuretic, is associated with a range of adverse effects primarily stemming from its potent natriuretic and diuretic actions, which can disrupt fluid and electrolyte balance. Side effects are generally similar across doses, though lower doses may be associated with a lower risk of severe effects such as significant electrolyte disturbances, dehydration, or ototoxicity, while high doses, rapid intravenous administration, renal impairment, and elderly age increase the likelihood of these effects. Common side effects include increased urination, thirst, dry mouth, dizziness, headache, muscle cramps or pain, weakness, nausea, vomiting, and diarrhea. These are often attributable to the drug's diuretic action and resulting fluid and electrolyte shifts. Electrolyte imbalances are among the most frequent adverse effects of furosemide. Hypokalemia occurs in approximately 20-30% of patients, particularly with higher doses or prolonged use, and can manifest as muscle weakness, cramps, or arrhythmias. Hyponatremia, hypomagnesemia, and metabolic alkalosis also commonly arise due to excessive loss of sodium, magnesium, and chloride, respectively, potentially leading to confusion, seizures, or cardiac issues in severe cases. Dehydration and volume depletion from furosemide's diuretic effect can result in orthostatic hypotension and low blood pressure, characterized by dizziness upon standing, and may contribute to a decline in renal function, including prerenal azotemia. These effects are more pronounced in patients with low fluid intake or concurrent conditions like heart failure. Ototoxicity is a serious but less common adverse effect, typically presenting as reversible hearing loss or tinnitus, though irreversible deafness has been reported. It is particularly associated with high intravenous doses exceeding 1 g, rapid infusion rates, or use in patients with severe renal impairment. Dermatological reactions include photosensitivity, which heightens the risk of severe sunburn, and bullous eruptions such as blistering on sun-exposed skin, resembling phototoxic responses. These are more likely with high doses and chronic exposure. Long-term use of furosemide carries risks including hyperuricemia, which can precipitate gout attacks or flare-ups, especially in predisposed individuals. It may also exacerbate hyperglycemia in patients with diabetes. Serious adverse effects can include profound electrolyte imbalances, dehydration, low blood pressure, irregular heartbeat (often secondary to electrolyte disturbances), ototoxicity, and severe allergic reactions. Recent data indicate an increased fracture risk due to hypocalcemia from enhanced urinary calcium excretion, with studies showing a 39% higher risk of fractures among users of loop diuretics.

Drug interactions

Furosemide, a , exhibits several significant drug interactions that can alter its efficacy or increase the risk of adverse effects, primarily through effects on renal function, electrolyte balance, and . These interactions necessitate careful monitoring and potential dose adjustments when co-administered with other medications. Co-administration of furosemide with antibiotics, such as gentamicin, or can potentiate due to additive renal tubular damage, as both classes of drugs impair renal function and increase the risk of , particularly in patients with pre-existing renal impairment. This interaction arises because furosemide may exacerbate the nephrotoxic effects of these agents, leading to higher serum concentrations and enhanced auditory nerve toxicity; such combinations should be avoided unless benefits outweigh risks, with audiometric monitoring recommended. Nonsteroidal anti-inflammatory drugs (NSAIDs), including indomethacin and ibuprofen, can reduce the natriuretic and antihypertensive effects of furosemide by inhibiting synthesis, which mediates afferent arteriolar and renal blood flow. This antagonism may result in diminished , elevated (BUN), creatinine levels, , and fluid retention, particularly in volume-depleted or elderly patients; concurrent use requires close renal function assessment. Furosemide can increase the risk of by decreasing its renal clearance through sodium depletion, which triggers compensatory proximal tubular reabsorption of sodium and ions. This leads to elevated serum levels, potentially causing neurological symptoms such as , , or seizures; co-administration is generally contraindicated, or doses must be reduced with frequent serum monitoring. The combination of furosemide with glycosides, such as , heightens the risk of hypokalemia-induced arrhythmias because furosemide promotes excretion, exacerbating digitalis toxicity on the myocardium. This interaction underscores the need for supplementation or monitoring of serum electrolytes and levels to prevent potentially fatal cardiac events. Angiotensin-converting enzyme (ACE) inhibitors, like or enalapril, can enhance the hypotensive effects of furosemide and increase the risk of , especially in patients with bilateral where efferent arteriolar dilation further compromises glomerular filtration. This synergistic renal hypoperfusion may precipitate or ; initiation of therapy should involve low doses with vigilant and monitoring.

Contraindications and precautions

Furosemide is contraindicated in patients with , as the drug relies on adequate renal function to exert its effect. It is also contraindicated in individuals with a history of to furosemide or other sulfonamides, due to the risk of and severe allergic reactions. However, in special cases where other diuretics are ineffective, furosemide may be used under strict medical monitoring, potentially with a small dose trial, skin testing, or desensitization protocols; this is not routinely recommended. Additionally, furosemide should not be used in cases of severe depletion until the imbalance is corrected, to avoid exacerbating , , or other disturbances. Precautions are necessary in patients with hepatic coma, where furosemide may precipitate and worsen ; therapy should be delayed until the patient's mental status improves. In individuals with , furosemide can elevate serum uric acid levels, potentially triggering acute attacks, necessitating close monitoring of urate levels. For patients with , the drug may induce and glucose intolerance, requiring vigilant blood glucose surveillance. Regular monitoring is essential during furosemide therapy, including periodic assessment of serum s (such as and sodium), renal function via () and levels, and audiometric evaluation in high-risk patients to detect early . These measures help prevent , , and imbalances that could arise from excessive . In special populations, elderly patients require dose adjustments starting at the lower end of the dosing range due to age-related declines in (GFR), with careful monitoring to avoid excessive volume depletion. Neonates warrant cautious use, with initial doses of 1-2 mg/kg and ongoing renal function monitoring, as furosemide can displace from binding sites, increasing the of kernicterus in jaundiced infants. Available data from observational studies have not demonstrated a of major birth defects, , or adverse maternal or fetal outcomes associated with furosemide use during . Animal reproduction studies in rabbits have shown maternal deaths and abortions at doses approximately 4 times the maximum recommended human dose. It should be used during only if the potential benefit justifies the to the , with monitoring for fetal growth. During breastfeeding, furosemide appears in and may cause or disturbances in the , so caution is advised, potentially requiring temporary discontinuation or close monitoring.

Overdose and toxicity

Overdose with furosemide primarily results from excessive diuretic activity, leading to profound and severe , which can progress to . Key symptoms include significant volume depletion, , and electrolyte derangements such as , , and hypochloremic ; profound may precipitate cardiac arrhythmias, including or . Acute high-dose administration, particularly intravenous doses exceeding recommended levels (such as rapid infusion of large boluses), can cause irreversible manifesting as , , or vertigo, especially in patients with renal impairment or . Similarly, excessive dosing may induce through profound fluid loss, resulting in characterized by or . Management involves immediate discontinuation of the drug, followed by supportive care including intravenous fluid resuscitation to restore volume and correct hypotension. Electrolyte replacement is essential, typically with potassium chloride for hypokalemia and magnesium sulfate for hypomagnesemia, alongside frequent monitoring of serum electrolytes, arterial blood gases, and blood pressure. Hemodialysis is ineffective for enhancing furosemide elimination due to the drug's high protein binding (91-99%). Prognosis is generally favorable with prompt intervention to address dehydration and imbalances, though delayed treatment may lead to persistent complications like renal failure or hearing loss. Case reports of accidental pediatric overdoses underscore the rapid onset of symptoms, often within hours of ingestion or administration, emphasizing the need for swift recognition in vulnerable populations.

Society and culture

Names and formulations

Furosemide is the (INN) recommended by the for this medication. The previous (BAN) was frusemide. The drug was first introduced commercially under the brand name Lasix by Hoechst Pharmaceuticals in 1966 as an oral tablet . Lasix remains a widely recognized brand for both oral and intravenous preparations of furosemide globally. In 2022, the U.S. approved Furoscix, a subcutaneous delivered via an on-body infusor, marking the first such delivery method for furosemide. In March 2025, the FDA expanded the label to include treatment of due to . Additionally, in August 2024, it was approved for patients with NYHA class IV . Furosemide is available in several standard , including immediate-release tablets in strengths of 20 mg, 40 mg, and 80 mg; oral solutions typically at 10 mg/mL or 40 mg/5 mL; and injectable solutions at 10 mg/mL for intravenous or intramuscular use. Sustained-release variants, such as matrix tablets incorporating polymers like hydroxypropyl methylcellulose or natural gums, have been formulated in research settings to extend effects but are not commonly marketed. Brand names vary by region, with examples including Fusid in . Following the expiration of original patents in the 1980s—stemming from the compound's initial patent in 1959—generic versions of furosemide have become widely available worldwide, contributing to its inclusion on the World Health Organization's List of . Furosemide is available exclusively by prescription and most countries worldwide, reflecting its status as a potent requiring medical supervision to manage risks such as imbalances. As a long-established generic , it is widely accessible and inexpensive; for example, a 20 mg oral tablet typically costs around $0.10 in the when purchased in standard quantities without insurance. In 2023, furosemide ranked as the 29th most prescribed drug , with approximately 19 million prescriptions dispensed annually, underscoring its common use in treating and . The U.S. (FDA) first approved furosemide in 1966 for both oral and intravenous administration to address conditions involving fluid overload. Regulatory authorities in granted similar authorizations in the mid-1960s through national approvals, enabling broad availability across the . Furosemide has been included on the World Health Organization's Model List of since 1977, highlighting its critical role in global healthcare for managing , renal disorders, and related conditions. In the context of sports, furosemide is prohibited by the (WADA) under the category of diuretics and masking agents, as it can dilute urine and potentially conceal the presence of other banned substances in human athletes. However, it is permitted for therapeutic use in horses during certain racing events under regulated conditions, such as to prevent , though its administration is strictly controlled to avoid performance enhancement. Supply chain challenges have occasionally affected furosemide availability in the , with reports of intermittent shortages for injectable formulations from 2022 to present (as of 2025) primarily attributed to delays at key producers.

Veterinary uses

In

Furosemide is primarily used in to prevent (EIPH), a condition where blood accumulates in the airways during intense exercise, particularly in racehorses. By acting as a , it reduces pulmonary capillary pressure and blood volume, thereby decreasing the incidence and severity of bleeding observed via after racing. This application targets and prone to EIPH, with administration typically occurring shortly before races to mitigate respiratory compromise and potential performance impacts. The standard dosing regimen for furosemide in equine involves intravenous administration of 250–500 mg per , approximately 4 hours prior to the race, corresponding to about 0.5–1.0 mg/kg body weight for an average 450–500 kg . This timing allows peak effects during exercise while minimizing prolonged fluid loss. Studies have demonstrated its efficacy, with prerace furosemide reducing EIPH severity in approximately 68% of affected horses and lowering overall incidence compared to controls under typical racing conditions. Regulatory frameworks for furosemide vary globally, with many U.S. racing jurisdictions, including those aligned with , permitting its use under strict protocols such as supervised administration and post-race plasma concentration thresholds (typically below 100 ng/mL). However, it is prohibited on race day in several international events, including select European and Asian races, to promote drug-free competition. In 2023, the Horseracing Integrity and Safety Authority (HISA) established an advisory committee to oversee independent studies on furosemide's effects, amid ongoing efforts to phase out race-day use for horses under certain ages or in high-profile stakes races like the . In horses, furosemide can induce adverse effects such as due to increased urinary excretion, leading to or cardiac irregularities if chronic. from may also occur, resulting in (up to 5–10% body weight) and reduced , which can impair despite its benefits for EIPH. Monitoring electrolytes and hydration is essential during repeated use in racing schedules. Furosemide gained approval for equine veterinary use in the early , driven by the industry's recognition of EIPH as a welfare and performance issue following advancements in endoscopic diagnosis. Initial approvals, such as by the California Horse Racing Board, addressed epistaxis in bleeders, establishing it as a cornerstone therapy amid growing concerns over respiratory health in high-speed equine athletics.

In companion animals

Furosemide is commonly used in companion animals, particularly dogs and cats, as a to manage conditions involving fluid overload, such as congestive (CHF) and associated , , or . It is also employed for due to , , , or high blood calcium levels, often in combination with other therapies to address the underlying cause. In dogs, it effectively reduces fluid accumulation from or non-inflammatory causes, while in cats, it helps control similar symptoms in chronic cardiac conditions. Administration in companion animals typically occurs orally via tablets or liquid suspensions, or parenterally through intravenous (IV), intramuscular (IM), or subcutaneous (SC) routes, with IV providing the fastest onset within 5 minutes for acute cases. For dogs, acute dosing is 2–4 mg/kg IV/IM/SC every 1–6 hours, transitioning to 2 mg/kg orally every 12 hours for maintenance (range 1–5 mg/kg every 8–12 hours); in cats, acute doses are 0.5–2 mg/kg IV/IM/SC every 1–8 hours, with maintenance at 1 mg/kg orally every 24 hours (range 1–2 mg/kg every 12–24 hours, up to 4–6 mg/kg/day). Oral bioavailability is approximately 40–50%, and dosing should ensure access to fresh water to prevent dehydration, with food recommended if gastrointestinal upset occurs. In refractory CHF cases, subcutaneous furosemide at a median of 5.5 mg/kg/day in dogs (divided every 12 hours) or 4.0 mg/kg/day in cats has shown efficacy in improving respiratory signs and owner satisfaction, with median survival of 106 days in dogs and 89 days in cats. Adverse effects in dogs and cats include increased thirst and urination (expected diuretic response), dehydration, electrolyte imbalances such as hypokalemia or hyponatremia, azotemia, vomiting, diarrhea, weakness, and metabolic alkalosis. Serious risks involve ototoxicity at high IV doses (>20 mg/kg in dogs), collapse, or lack of urine production, necessitating immediate veterinary attention. Subcutaneous administration is generally well-tolerated but may cause mild skin reactions like irritation or alopecia in about 15–18% of cases, which are manageable by site rotation or antibiotics. Precautions include avoiding use in animals with , , or to sulfonamides, and cautious application in those with , , or due to risks of shifts or reduced efficacy. Monitoring involves regular blood tests for function, s, and hydration status, along with weight and checks to adjust dosing and prevent complications. show a short IV of about 1 hour and longer oral terminal of 7 hours in dogs, with primary via (55%) and (45%), emphasizing the need for renal function assessment.

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