Heart diseases make up approximately 10% of the cases seen in clinics according to statistics. So, what drug can you choose, when you want the best chance of long-term reliable therapy, as well as acute treatment? One choice is Furosemide. Also known under its generic name as Lasix. 

Furosemide is a fast-acting diuretic drug recommended by the American College of Veterinary Internal Medicine. Furosemide uses include treatment of Congestive Heart Failure in dogs, lung fluid retention and even some kidney diseases. Take a read below if you want to know more about the interactions, dosage and side effects of Furosemide! 

Dilated cardiomyopathy by I Love Veterinary

Severe dilated cardiomyopathy in a boxer mix that presented for coughing and “fainting” episodes. Started on vetmedin, enalapril, and lasix.

Uses of Furosemide 

Furosemide is most often used to lessen the symptoms of Congestive Heart Failure, whether the condition is acute or chronic. 

Heart diseases in dogs are often “silent” or asymptomatic for a long period. This is because the heart is well-protected by the ribcage and difficult to see. Meaning, heart diseases are often difficult to detect, for both owners and clinicians. 

This is the reason that some dogs will walk around with undetected long-term heart conditions. Sometimes for years. Meanwhile, the heart is trying to compensate. All this leading to the development of Congestive Heart Failure.

Congestive Heart Failure is an abnormality in the heart. It ultimately results in the heart being unable to pump enough blood around the body. It’s not a disease as such, but rather a condition of the final consequences of heart failure.

Owners are not necessarily always aware of the symptoms to look out for. This can mean that the dog can quite suddenly present in the clinic with acute symptoms. Often in critical condition. 

Congestive Heart Failure and Furosemide therapy by I Love Veterinary

Luckily in both acute and chronic cases, Furosemide can be the drug of choice. 

In acute heart failure patients Furosemide can be administered. Often along with Pimobendan and of course emergency therapy like oxygen. 

In patients who are stable, but still need reliable chronic therapy Furosemide can also be useful. Here it can relieve the symptoms of chronic Congestive Heart Failure. Often given along with Pimobendan and ACE-inhibitors. 

Furosemide acts at the Loop of Henley in the kidneys. Here it affects the urinary excretion. It does this by interacting with the sodium- and chloride ions present. Promoting increased excretion of water through the urine. This causes a reduction of fluid volume and subsequently venous filling pressure and preload. Leading to alleviating some of the pressure on the heart. 

As well as having a diuretic effect, Furosemide also acts as a mild dilator. Thereby decreasing systemic venous pressure – especially when administered through IV. 

Furosemide can also be used to treat other conditions, for example: 

  • Edema (fluid accumulations)
  • Some forms of acute kidney failure 
  • Lung fluid retention 

Side effects of Furosemide in Dogs by I Love Veterinary

Side effects of Furosemide in Dogs 

As with all types of drugs, some side effects can be observed when using Furosemide. These include: 

  • Increased thirst and urination
  • Soft faeces or diarrhea
  • Loss of electrolytes in the urine. Leading to weakness and increased risk of heart arrhythmias. Especially in patients that aren’t eating enough.
  • Potential increase in blood sugar levels. A risk to diabetic patients. 
  • Potential for resulting in low blood pressure in patients with pericardial effusion. 

Mild side effects will often pass with time, with little or no action needed. More severe side effects can however need treatment. Therefore it is important to continuously monitor patients being treated with Furosemide. Especially if excessive side effects occur. Also, because Congestive Heart Failure is a progressive disease. The treatment plan might need to change with time. 

Congestive Heart Failure and Furosemide treatment by I Love Veterinary

10-year-old Chihuahua with an enlarged heart

Furosemide Drug Interactions 

Furosemide is often given in combination with other drugs when used for treating Congestive Heart Failure. 

Acute Congestive Heart Failure

In these cases oxygen is the first thing that should be provided to the patient. This is to ensure an increase in tissue oxygenation. Pimobendan is administered to cause vasodilation and Furosemide to increase diuretics. The goal is to ensure that the heart is capable of pumping enough oxygenated blood around the body. Thereby increasing the chance of survival for the patient. 

Chronic Congestive Heart Failure

The aim of treatment of Chronic Congestive Heart Failure is to prolong the life of the patient. As well as improving quality of life, as the condition can rarely be cured. To do this, Furosemide is often used in combination with three other drugs:

  • Pimobendane
  • An ACE-inhibitor, like Enalapril
  • Spironolactone

Adverse interactions: 

Some drugs should only be used cautiously in interaction with Furosemide. 

  • ACE inhibitors: They’re often used in combination to treat Congestive Heart Failure. However, any Veterinary clinician should be aware of the risk of the patient developing too low blood pressure when these two drugs interact. 
  •  Aminoglycoside antibiotics: Long-term use along with some antibiotics. Gentamicin as an example, can increase the risk of the patients developing hearing loss and deafness.

It is always important to ask the owners whether the dog is currently on any other medication. That includes vitamins or supplements.  Especially if it’s not your regular patient.

Furosemide Drug Interactions by I Love Veterinary

Administration and Dosage of Furosemide for Dogs 

Never give any medication to your dog before consulting your veterinarian first and getting the correct prescribed amount from the vet. Furosemide is available most places in oral tablets or parenteral formulations. 

Peroral administration

Furosemide is absorbed fast after PO administration. But, incompletely, with a bioavailability of 40-50%. After PO administration it starts taking effect within 60 minutes. Reaching peak effect within 1-2 hours and effect wearing off after around 6 hours. It can be given with or without food. If vomiting occurs when given to the patient on an empty stomach, future doses should be with food. 

In dogs the standard dosage is: 2.5mg/kg, q24h.

Parenteral administration

For life-threatening Congestive Heart Failure, it might be necessary to administer Furosemide parenterally. This is to ensure faster action within the body. The dosage is determined by the veterinarian based on the state of the animal when it arrives at the clinic. 

In dogs the standard dosage is: 2-4mg/kg, every 1-6h, IV, IM or SC.

 As an alternative, a constant rate infusion of 0.25-1 mg/kg/hr is administered. 

Administration and Dosage of Furosemide for Dogs by I Love Veterinary

Administration of dosages above the recommended level could cause severe problems. For example: 

  • Deafness
  • Disturbances of the electrolyte balance 
  • Central Nervous System affects
  • Cardiovascular disorders 

Furosemide needs to be stored at 15-30 degrees Celsius and away from light. 

Synonyms or brand names for Furosemide include Lasix, Salix, Libeo and Furosoral. 

Summary

In the end Furosemide is a very useful drug when working with companion animals in the clinic. Often assisting in either saving the life of critically ill animals in acute heart failure. Or, providing long-term reliable therapy for chronically ill animals. Ensuring the animals can live a longer and better life despite their heart conditions.