|by mouth, IV, IM|
|Metabolism||liver and kidney glucuronidation|
|Onset of action||30 to 60 min (PO), 5 min (IV)|
|Elimination half-life||up to 100 minutes|
|Excretion||renal 66%, biliary 33%|
|Chemical and physical data|
|Molar mass||330.745 g/mol|
|3D model (JSmol)|
Furosemide, sold under the brand name Lasix among others, is a medication used to treat fluid build-up due to heart failure, liver scarring, or kidney disease. It may also be used for the treatment of high blood pressure. It can be taken intravenously or by mouth. When taken by mouth, it typically begins working within an hour, while intravenously, it typically begins working within five minutes.
Common side effects include low blood pressure with standing, ringing in the ears, and sensitivity to sunlight. Potentially serious side effects include electrolyte abnormalities, low blood pressure, and hearing loss. Blood tests are recommended regularly for those on treatment. Furosemide is a type of loop diuretic that works by decreasing the reabsorption of sodium by the kidneys.
Furosemide was discovered in 1962. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale price in the developing world is between US$0.004 and 0.02 per day. In the United States it is available as a generic medication and costs about $0.15 per day. Furosemide is on the World Anti-Doping Agency's banned drug list due to concerns that it may mask other drugs. It has also been used to prevent and treat race horses for exercise-induced pulmonary hemorrhage.
Furosemide is primarily used for the treatment of hypertension and edema. It is the first-line agent in most people with edema caused by congestive heart failure. It 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.
- It is excreted by tubular secretion, so in severe kidney impairment (GFR 5–10 ml/min), lower doses are required due to accumulation in the body.[medical citation needed] It also can cause further kidney damage and should be administered with caution.
- Furosemide acts within 1 hour of oral administration (after IV peak effect within 30 minutes); diuresis is complete within 6 hours (for oral administration) and 2 hours (for IV administration).
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.
Furosemide has potential interactions with these medications:
- Aspirin and other salicylates
- Other diuretics (e.g. ethacrynic acid, hydrochlorothiazide)
- Synergistic effects with other antihypertensives (e.g. doxazosin)
Potentially hazardous interactions with other drugs:
- Analgesics: increased risk of kidney damage (nephrotoxicity) with nonsteroidal anti-inflammatory drugs; antagonism of diuretic effect with NSAIDs
- Antiarrhythmics: a risk of cardiac toxicity exists with antiarrhythmics if hypokalemia occurs; the effects of lidocaine and mexiletine are antagonized.
- Antibacterials: increased risk of ototoxicity with aminoglycosides, polymyxins and vancomycin; avoid concomitant use with lymecycline
- Antidepressants: increased risk of hypokalemia with reboxetine; enhanced hypotensive effect with MAOIs; increased risk of postural hypotension with tricyclic antidepressants
- Antiepileptics: increased risk of hyponatremia with carbamazepine
- Antifungals: increased risk of hypokalemia with amphotericin
- Antihypertensives: enhanced hypotensive effect; increased risk of first dose hypotensive effect with alpha-blockers; increased risk of ventricular arrhythmias with sotalol if hypokalemia occurs
- Antipsychotics: increased risk of ventricular arrhythmias with amisulpride, sertindole, or pimozide (avoid with pimozide) if hypokalemia occurs; enhanced hypotensive effect with phenothiazines
- Atomoxetine: hypokalemia increases risk of ventricular arrhythmias
- Cardiac glycosides: increased toxicity if hypokalemia occurs
- Cyclosporine: variable reports of increased nephrotoxicity, ototoxicity and hepatotoxicity
- Lithium: risk of toxicity.
Mechanism of action
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 chloride transport channel, thus causing sodium, chloride, and potassium loss in urine.
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 development of acidosis, as it is with the carbonic anhydrase inhibitors.
Additionally, furosemide is a noncompetitive subtype-specific blocker of GABA-A receptors. Furosemide has been reported to reversibly antagonize GABA-evoked currents of α6β2γ2 receptors at µM concentrations, but not α1β2γ2 receptors. During development, the α6β2γ2 receptor increases in expression in cerebellar granule neurons, corresponding to increased sensitivity to furosemide.
- Molecular weight (daltons) 330.7
- % Bioavailability 47-70%
- % Protein binding 91–99
- Volume of distribution (L/kg) 0.07 – 0.2
- Volume of distribution may be higher in patients with cirrhosis or nephrotic syndrome
- Approximately 10% is metabolized by the liver in healthy individuals, but this percentage may be greater in individuals with severe renal failure 
- Renal clearance (mL/min/kg) 2.0
- Elimination half-life (hrs) 2
- Time to peak concentration (hrs)
The pharmacokinetics of furosemide are apparently not significantly altered by food.
No direct relationship has been found between furosemide concentration in the plasma and furosemide efficacy. Efficacy depends upon the concentration of furosemide in urine.
Some of the brand names under which furosemide is marketed include: Aisemide, Apo-Furosemide, Beronald, Desdemin, Discoid, Diural, Diurapid, Dryptal, Durafurid, Edemid, Errolon, Eutensin, Flusapex, Frudix, Frusetic, Frusid, Fulsix, Fuluvamide, 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.
The diuretic effects are put to use most commonly in horses to prevent bleeding during a race. Sometime in the early 1970s, furosemide's ability to prevent, or at least greatly reduce, the incidence of bleeding (exercise-induced pulmonary hemorrhage) by horses during races was discovered accidentally. In the United States of America, pursuant to the racing rules of most states, horses that bleed from the nostrils three times are permanently barred from racing. Clinical trials followed, and by decade's end, racing commissions in some states in the USA began legalizing its use on race horses. On September 1, 1995, New York became the last state in the United States to approve such use, after years of refusing to consider doing so. 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.
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.
It is also used to treat congestive heart failure (pulmonary edema, pleural effusion, and/or ascites) in cats and dogs. It can also be used in an attempt to promote urine production in anuric or oliguric acute renal failure.
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 risk of kidney or ear damage), and trimethoprim sulfa (causes decreased platelet count). It may also cause interactions with anesthesics, so its use should be related to the veterinarian if the animal is going into surgery, and 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.
The drug is best not used during pregnancy or in a lactating mare, as it has been shown to be passed through the placenta and milk in studies with other species. It should not be used in horses with pituitary pars intermedia dysfunction (Cushings).
Furosemide is detectable in urine 36–72 hours following injection. Its use is prohibited by most equestrian organizations.
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