Furosemide is a potent diuretic. It acts by inhibiting the reabsorption of electrolytes within the kidney. The excreted electrolytes then "draw'" excess water along with them.
Furosemide is used in the treatment of non-inflammatory edema (e.g., allergic reaction, heart failure, excessive swelling of the udder after weaning). Furosemide has also been used extensively to help control the severity and frequency of "lung bleeding" in racehorses, although this is not an FDA-approved use of this drug.
The recommended dose of furosemide is 0.5 mg/lb of body weight, or approximately 1.0 mg/kg of body weight. Tablets are available (human preparations), or large boluses (bovine formulation), but the usual route of administration for horses is intravenous or intramuscular.
In cases of heart failure, other appropriate cardiac medications should be continued.
The major side effect of all diuretics is the danger of dehydration and electrolyte imbalance. Of particular importance is potassium, which is lost in increased amounts in the urine. Furosemide may also cause decreased levels of blood calcium. Both of these electrolytes are important in normal functioning of heart and skeletal (body) musculature.
Rapid intravenous injection, particularly at high dosages, has been reported to cause a temporary hearing loss in experimental cats.
Furosemide should be used with great caution, if at all, in cases where renal (kidney) function may be impaired; with preexisting dehydration and known, or suspected electrolyte imbalance; and, in horses with liver disease or suspected tumors of the pituitary gland. (In the latter. furosemide may cause a worsening of the centrally induced diabetes.)
The concurrent use of corticosteroids in horses treated with furosemide can result in worsening of potassium and calcium loss.
The concurrent use of furosemide and aminoglycoside (the -mycin group antibiotics may result in increased risk of damage to the kidneys or deafness.
Furosemide may decrease the response to drugs such as epinephrine used to maintain blood pressure during general anesthesia. Furosemide can also decrease sensitivity to commonly used paralyzing agents (e.g., curare! a horse may receive during general anesthesia. Furosemide may increase the sensitivity to other paralyzing agents (e.g., succinylcholine). Therefore, furosemide should not be given for at least one day prior to general anesthesia. THE SURGEON AND ANESTHETIST SHOULD BOTH BE INFORMED IF THE HORSE HAS A HISTORY OF RECEIVING FUROSEMIDE AND REQUIRES EMERGENCY SURGERY.
Concurrent use of furosemide and trimethoprim may result in increased likelihood of the development of low platelet Counts.
Furosemide is not recommended for use in breeding stock.
Furosemide may cause fetal malformations and is contraindicated during pregnancy.
Furosemide appears in the breast milk of other species. It should be used with caution in nursing mares, particularly when they have very young foals.
ARCI: Furosemide is currently an unlisted drug in the ARCI classification system, but under consideration for classification as a Class 4 drug.
Detection Time Information: In many racing jurisdictions, furosemide is a permitted drug for use in prevention of exercise-induced pulmonary hemorrhage (bleeding). Its pharmacological effects after an intravenous dose are not thought of as lasting for longer than 5-6 hours, although the effects may last longer after intramuscular administration of the drug. Because furosemide can dilute out certain drugs and drug metabolites in equine urine, the generally recommended dose in the treatment of lung bleeding is 250 mg/horse not less than 4 hours prior to post. Such a dose of furosemide can be detected in urine with relative ease for 36 hours and with some effort, for 72 hours after drug administration, although most chemists will not report the drug at 72 hours post dosing. There is a blood concentration limit in some states of 50 parts/billion (ppb) in blood.
Canadian authorities report a 36-hour detection time Furosemide is a common Source of medical violations.
Rules of Governing Bodies
Standardbred and Thoroughbred Racing: Standardbred and thoroughbred racing operates under a basic drug-free policy. However, individual state racing commissions may permit individual therapeutic drugs, often at certain previously established "permissible" blood levels. Check with the commission in your state.
Horseman's Comments and Conclusion to this article at the bottom of this page.
Type of Drug Diuretic.
Congestive heart failure, cirrhosis of the liver, kidney dysfunction, high blood pressure, and other conditions where it may be desirable to rid the body of excess fluid. (1)
Furosemide causes the production of urine by affecting the kidneys. It may also cause lowered blood pressure. Furosemide is particularly useful as a very strong drug with great diuretic potential, when a drug with less diuretic potential would fail to produce the desired therapeutic effect.
If given in excessive quantities, Furosemide will cause depletion of water and electrolytes. (3) It should not be taken without constant medical supervision and without the dose being adjusted to your particular needs. (2) You should not take this drug if your production of urine has been decreased abnormally by some type of kidney disease, or if you feel you may be allergic to it or have experienced an allergic reaction to it in the past.
Excessive use of Furosemide will result in dehydration or reduction in blood volume and may cause circulatory collapse and other related problems, particularly in older adults. In addition, because of the potent effect that this drug has on the electrolytes in the blood-potassium, sodium, Carbon dioxide, and others-frequent laboratory evaluations of these electrolytes should be performed during the few months of therapy and periodically afterward. (4)
pregnancy /Breast -feeding
Although Furosemide has been used to treat specific conditions in pregnancy, it should generally not be used to treat a pregnant woman because of its potential effects on the unborn child. Although this effect has not been seen in humans, Furosemide can cause kidney problems in unborn animals if given to animals during pregnancy. If your doctor feels that your case warrants the use of Furosemide, the decision to use this drug must be made by you and your doctor based on the potential benefits derived from this drug as opposed to the potential problems that may be associated with its use.
If you must take this drug during the period that you are nursing a newborn baby, you should stop nursing and feed the baby prepared formulas.
Older adults are more sensitive to the effects of this drug. Follow your doctor's directions and report any side effects at once.
If you are taking Furosemide you should be aware that changes may develop in potassium and other electrolyte concentrations in your body. In the case of hypokalemia (lowered potassium) produced by Furosemide, you may observe these warning signs: dryness of the mouth, thirst, weakness, lethargy, drowsiness, restlessness, muscle pains or cramps, muscular tiredness, low blood pressure, decreased frequency of urination and decreased amount of urine produced, abnormal heart rate, and stomach upset, including nausea and vomiting. To treat this, potassium supplements are given in the form of tablets, liquids, or powders, or consumption of potassium-rich foods such as bananas, citrus fruits, melons, and tomatoes is increased.
Furosemide may alter the metabolism of sugar in your body. If you have diabetes mellitus, you may develop high blood sugar or sugar in the urine while you are taking the drug. To treat this problem, the dose of drugs that you are taking to treat your diabetes will have to be altered.
In addition, people taking Furosemide have experienced (5) one or more of the following side effects: abdominal discomfort, nausea, vomiting, diarrhea, rash, dizziness, lightheadedness, weakness, headache, blurred vision, fatigue, jaundice (yellowing of the skin or whites of the eyes), acute attacks of gout, ringing in the ears, reversible periodic impairment in hearing. There have also been some reported cases of irreversible hearing loss.
Other side effects are dermatitis, unusual skin reactions, tingling in the extremities, postural hypotension (or dizziness on rising quickly from a sitting or lying position), and anemia of various types. Rare side effects include a sweet taste in the mouth, burning feeling in the stomach and/or mouth, thirst, increased perspiration, and frequent urination.
Furosemide will increase (potentiate) the action of other blood-pressure-lowering drugs. This is beneficial and is frequently used to help lower blood pressure in patients with hypertension.
The possibility of developing electrolyte imbalances in body fluids is increased if you take other medications such as Digitalis and adrenal corticosteroids while you are taking Furosemide.
If you are taking Furosemide because of congestive heart failure and are also taking Digitalis, loss of potassium may significantly affect the toxicity of Digitalis.
If you are taking an oral antidiabetic drug and begin taking Furosemide, the antidiabetic dose may have to be altered.
If you are taking Lithium Carbonate, you should probably not take a diuretic, which, by reducing the elimination of Lithium from the blood, adds a high risk of Lithium toxicity.
Interaction with aminoglycoside antibiotics may cause periodic hearing losses; make sure your doctor knows you are taking Furosemide before he or she gives you an injection of an aminoglycoside.
If you are taking high doses of Aspirin to treat arthritis or similar diseases, and you begin to take Furosemide, you may have to lower the dose of Aspirin because of the effect Furosemide has on passage of Aspirin through the kidneys.
If you are taking Furosemide for the treatment of high blood pressure or congestive heart failure, avoid over the counter drug products for the treatment of coughs, colds. and allergies which may contain stimulant drugs. Check with your pharmacist, who can give you accurate information about any over-the-counter drug and its potential interactions with Furosemide.
Foods that are high in potassium, including bananas, citrus fruits, melons, and tomatoes, should be given high priority in your daily diet.
Adult: 20 to 80 milligrams per day, depending on disease and patient's response. Doses of 600 milligrams per day or even more have been prescribed.
Infant and child: 4 to 5 milligrams per pound of body weight daily in a single dose. If therapy is not successful, the dose may be increased by steps of 2 to 5 milligrams, but not to more than 14 to 15 milligrams per day.
Maintenance doses are adjusted to the minimum effective level.
If the amount of urine you produce each day is dropping or if you suffer from significant loss of appetite, (6) muscle weakness, tiredness, or nausea while taking this drug, contact your doctor immediately.
Furosemide is usually taken once a day, after breakfast. If a second dose is needed, it should be taken no later then 2 in the afternoon. This is to avoid waking up during the night to urinate.
If you forget to take the dose of Furosemide, take it as soon as you remember. If it is almost time for your next regularly scheduled dose, skip the one you forgot and continue with your regular schedule. Do not take a double dose.
The use of this drug is very controversial. I will refrain form saying whether is should be used or not. In the 70s this drug was legal to use freely by trainers and vets on the track in various states. Because of its performance enhancing qualities, mainly when used for the first time, some of the racing commissions decided to monitor the use of this drug. Believe it or not, this resulted in much wider use of this drug than before it was monitored. In the seventies there was noticeably much less "bleeders" to be seen on the track than in these days.
I have not used this drug on horses often, mainly because of the problems with the regulations. It is very easy to get the horse on the "Lasix" list, however to get him off is quite another story. Racetrack folks and vets should know why. I believe that if this drug is used, it should be listed in the program/Racing Form as it is now, however greater freedom should be given to trainers and vets to put the horses on and off the Lasix list. I believe this will drastically lower the abuse of this drug. It will give a chance to the trainer or the vet to see and compare the performance of the horse with or without the use of Lasix. (Some horse do well on it and some don't. A trainer knows his horse the best. He should have the highest authority to decide whether the horse should be on Lasix or not. Veterinarian should only approve or disapprove. Veterinarian involvement in this case is imperative!)
The racing commissions are concerned in this case with "race fixing", while forgetting the welfare of the horse. There was always "race fixing" and always will be. It is a part of racing industry and since the entire sport is based on gambling it does need to be controlled. However, the "race fixing" is not as widely spread as most folks would have you believe, thanks to the states racing commissions. The bigger the purses, the less race fixing. Often on the small tracks the horse when he wins barely pays his feed bill, so to speak, and as they say; "We've got to eat and so do the horses". The racing industry is of great importance to many state economies. Folks should support it and improve it by education and not by legislation alone. They should remember the horses, because of them many people in this world have a food on the table.
All my comments are merely my opinions and beliefs gained from 40 years of professional life with horses. All drugs should be used only by the consent of a veterinarian and according to his instructions. A person who is with the horse everyday, should know him better than anyone else.
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