Frusemide

Furosemide (INN) or frusemide (former BAN) is a loop diuretic used in the treatment of congestive heart failure and edema. It is most commonly marketed by Sanofi-Aventis under the brand name Lasix. It has also been used to prevent Thoroughbred and Standardbred race horses from bleeding through the nose during races.

Along with some other diuretics, furosemide is also included on the World Anti-Doping Agency's banned drug list due to its alleged use as a masking agent for other drugs.

Medical uses

Furosemide is primarily used for the treatment of two conditions: hypertension and edema. It is the first line agent in most people with edema due to congestive heart failure.

• Edema associated with heart failure, hepatic cirrhosis, renal impairment, nephrotic syndrome
• Hypertension
• Adjunct in cerebral/pulmonary edema where rapid diuresis, i.e. lowering body water content by inducing urination, is required (IV injection)

It is also sometimes used in the management of severe hypercalcemia in combination with adequate rehydration.

Adverse effects

Although disputed, it is considered ototoxic: "usually with large parenteral doses and rapid administration and in renal impairment" Furosemide also can lead to gout due to hyperuricemia. Hyperglycemia is also a common side effect.

The tendency, as for all loop diuretics, to cause low potassium levels (hypokalemia) has given rise to combination products, either with potassium itself (e.g. Lasix-K) or with the potassium sparing diuretic of amiloride (Co-amilofruse).

Interactions

Furosemide has potential interactions with the following medications:

• Aminoglycoside antibiotics such as gentamicin
• Aspirin and other salicylates
• Other diuretics (e.g. ethacrynic acid, hydrochlorothiazide)
• Indomethacin
• Lithium
• Synergistic effects with other antihypertensives (e.g. doxazosin)
• Sucralfate

Mechanism of action

Main article: Loop diuretic

Furosemide, like other loop diuretics, acts by inhibiting NKCC2, the luminal Na-K-2Cl symporter in the thick ascending limb of the loop of Henle. 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.

Due to 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.

By inhibiting the transporter, the loop diuretics reduce the reabsorption of NaCl and also diminish the lumen-positive potential that derives from K⁺ recycling. This electrical potential normally drives divalent cation reabsorbtion in the loop, and by reducing this potential, loop diuretics cause an increase in Mg²⁺ and Ca²⁺ excretion. Prolonged use can cause significant hypomagnesemia in some patients. Since Ca²⁺ is actively reabsorbed in the distal convoluted tubule, loop diuretics do not generally cause hypocalcemia.

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.

Brand names

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, Furosedon, Fusid.frusone, Hydro-rapid, Impugan, Katlex, Lasilix, Lasix, Lodix, Lowpston, Macasirool, Mirfat, Nicorol, Odemase, Oedemex, Profemin, Rosemide, Rusyde, Salix, Trofurit, Uremide and Urex. The name Lasix is derived from the phrase "lasts six (hours)" — referring to its duration of action. Intravenous and oral Lasix lasts two to four hours.

Veterinary uses

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 (EIPH) by horses during races was discovered accidentally. Pursuant to the racing rules of most states, horses that bleed from the nostrils three times are permanently barred from racing (for their own protection). Clinical trials followed, and by decade's end, racing commissions in some states 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." However, its use for this purpose is still prohibited in many other countries, and veterinarians dispute its use for this problem.

Furosemide is also used in horses for pulmonary edema, congestive heart failure (in combination with other drugs), and allergic reactions. Despite the fact 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 in canines (who experience fluid on the lungs) due to complications from heartworms. It can be used in conjunction with an antibiotic and anti-inflammatory to treat this condition.

Precautions, side effects, and administration for horses

Furosemide is injected either intramuscularly (IM) or intravenously (IV), usually 0.5-1.0 mg/kg 2x/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. It is especially important to prevent potassium loss. 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, GI 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 kidney's 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.