(for veterinary information only)
BRAND NAME: LASIX, DISAL, SALIX
The kidney is one of the most complicated organs of the body. It is responsible for maintaining one’s electrolyte balance, blood pressure, and fluid/hydration status through its elaborate filtration and excretion systems. It is not our intention to review a system as complex as this here; with regard to furosemide, what is important to know is that it acts on the kidney to increase the body’s loss of water, assorted minerals, and assorted electrolytes (salt, potassium, calcium, magnesium, bicarbonate, hydrogen and ammonium).
HOW THIS MEDICATION IS USED
Because furosemide leads to water loss via increased urine production it is classified as a “diuretic.” This makes it a useful medication in conditions where the removal of excessive fluids would be beneficial. Such conditions include:
Inherent to all diuretics, including furosemide, are the following side effects:
Furosemide is associated with an increase in blood sugar levels. This is not a problem for most patients but a different diuretic may be a better choice for a diabetic patient.
Hearing loss has been reported, especially in cats, when large amounts of injectable lasix have been used in a crisis.
Urination is usually seen within 30 minutes
INTERACTIONS WITH OTHER DRUGS
One of the most common drug interactions to be aware of is the interaction between furosemide and vasodilating heart medications (especially the Angiotensin Converting Enzyme inhibitors such as enalapril, benazepril, and lisinopril). Furosemide will decrease circulating blood volume as it causes a depletion in body water. This means that the kidney (and most other organs) will have a reduced blood flow to them. The patient’s kidney and electrolyte balance must stabilize before a vasodilator is added in. If the vasodilator is added too soon, it too will reduce blood flow to the kidney and the kidney will fail, possibly permanently. These medications are frequently used together in heart failure patients. To avoid problems, the patient should be assessed biochemically with a blood test prior to the addition of the vasodilator. If all is normal, the vasodilator may be started and renal blood parameters should be rechecked 3-5 days later. If they are still normal, then the above kidney issues should not be a problem; however, should another heart failure crisis arise and large doses of injectable lasix be required to resolve it, kidney values should again be checked 3-5 days later.
The airway dilator theophylline may be able to reach higher blood levels when used in conjunction with furosemide. This means that the theophylline dose may need to be reduced.
Furosemide is often used concurrently with digitalis derivatives. If furosemide leads to a significant drop in blood potassium levels, this can increase the risk of heart rhythms disturbances and other signs of digitalis toxicity.
Furosemide is often used in combination with prednisone to reduce serum calcium levels. It is possible for this combination of medication to lead to a reduction in potassium level significant enough to require potassium supplementation.
Aminoglycoside antibiotics (amikacin, gentamicin etc.) have properties that make them toxic to the ear and to the kidney. These properties increase with concomitant use of furosemide.
CONCERNS AND CAUTIONS
Obviously it is best not to use this medication in a dehydrated patient if water is being restricted.
Weakness or lethargy could be an indicator that blood potassium has dropped too low. Be sure to inform your veterinarian if your pet seems listless.
Because of the increased calcium excretion brought on by furosemide (i.e. an increase in urinary calcium levels), there could be a problem using this medication in patients with a history of calcium oxalate bladder stone formation.
It is extremely difficult to overdose with this medication. Toxic doses reported are over 100 times a typical oral dose of medication. It is important to realize that in the treatment of heart failure (this drug’s primary use), a crisis can arise at any time. Often giving an extra dose of oral medication can be a life saving procedure. Be sure you understand what signs you are to watch for to determine if an extra dose or two should be administered and when you should definitely rush to the vet’s office.
The loss of water-soluble vitamins or urine can be a problem for patients receiving diuretics. Prescription diets for heart and kidney disease are vitamin-fortified with these extra losses in mind. Patients that refuse to eat such prescription diets should probably receive a vitamin supplement.
Furosemide should be used with caution in diabetic patients as they are already prone to abnormalities in electrolyte balance (which could be exacerbated by the electrolyte shifts employed by furosemide).
Page last updated: 4/18/2019