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Digoxin for Veterinary Use
by Barbara Forney, VMD
Digoxin and the other digitalis glycosides have direct effects on cardiac muscle and affect the electrical conduction in the heart. Digoxin increases cardiac output by increasing myocardial contractility. It also decreases sympathetic tone and as a result causes increased diuresis and a reduction of edema. The overall result is a reduction in heart size, heart rate, blood volume, and pulmonary and venous pressures.
The electrocardiac effects of digitalis include slowing the conduction velocity at the AV node and a prolonged effective refractory period. Other electrocardiographic effects are an increased PR interval, decreased QT interval and depression of the ST segment.
Dogs and Cats
Digoxin traditionally has been used to treat congestive heart failure in both dogs and cats. It usually is used in conjunction with other medications including diuretics and angiotensin-converting enzyme (ACE) inhibitors.
Although digoxin has improved and probably prolonged the quality of life for many veterinary cardiac patients, it remains a drug that requires careful monitoring. It has a narrow margin of safety and there is significant variation in absorption between patients. Cats in particular have a high incidence of toxicity although toxicity also occurs in approximately 25% of dogs. The absorption of digoxin may be affected by food and by the formulation of the medication. It usually is given on an empty stomach and the dose may need readjustment with any change in formulation or manufacturer. Cats frequently dislike the taste of digoxin elixir and some investigation of flavoring alternatives is helpful. Digoxin dosing should be based on lean bodyweight with adjustment for ascites and fat. Digoxin is excreted by the kidneys and the dose may need to be adjusted downward for animals with renal disease. Serum digoxin levels should be followed carefully in both dogs and cats particularly when starting on treatment. With the advent of newer cardiac medications, some veterinary cardiologists are less likely to use digoxin as a first-line drug.
Digoxin Side Effects
- The most prominent adverse side effects may be due to digitalis toxicity. They may include both cardiac and GI symptoms. The cardiac symptoms can resemble worsening of the underlying heart disease making it difficult to differentiate. It may be necessary to monitor serum digoxin levels and possibly discontinue therapy while determining the underlying cause.
- Adverse cardiac effects include many different arrhythmias: heart block (complete and incomplete), paroxysmal atrial or ventricular tachycardias, multifocal premature ventricular contractions, bigeminy and ST-segment changes.
- Gastrointestinal side effects include anorexia, nausea and diarrhea.
- Other side effects include central nervous system disturbances, unsteady gait and depression. Collie breeds may be more sensitive to CNS effects.
- Digoxin should not be used in animals with ventricular fibrillation or those with digitalis intoxication.
- Digoxin may be used with caution in the following conditions: heart failure with glomerulonephritis, idiopathic subaortic stenosis, acute myocardial infarction, myocarditis, myxedema, chronic obstructive pericarditis, ventricular tachycardias, premature ventricular contraction, incomplete AV block, severe pulmonary disease or hypoxia and carotid sinus sensitivity.
- Digoxin generally is not recommended for use in cats with feline hypertrophic cardiomyopathy.
- Digoxin may be used in some patients with bradycardia or complete AV block, provided that the block was not caused by digoxin.
- Animals in atrial fibrillation should be taken off digoxin at least one to two days prior to attempts at electrical conversion.
- Animals with renal or thyroid disease may require more frequent monitoring of electrolytes and digoxin levels. Animals with serum electrolyte abnormalities, particularly hypokalemia, may require smaller doses and should be monitored very carefully.
- There are many important drug interactions for digoxin. Additional information should be sought when using digoxin with the following drugs:
- Drugs that decrease digoxin absorption:
antacids, cimetidine, metoclopramideoral neomycin, some chemotherapy agents and penicillamine.
- Drugs that increase digoxin levels or slow the elimination of digoxin:
diazepam, quinidine, anticholinergics, succinycholine, verapamil, tetracycline and erythromycin.
- Drugs that decrease serum potassium and may predispose patients to digoxin toxicity:
diuretics, amphotericin B, corticosteroids, ACTH, some laxatives, glucagon, dextrose or dextrose/insulin infusion and sodium polystyrene sulfonate.
- Thyroid-replacement therapy and spironolactone may affect digoxin levels.
- Symptoms of chronic toxicity are discussed under side effects. The drug may need to be stopped temporarily while re-evaluating the dose. Drugs used to treat digitalis-induced arrhythmias include lidocaine, phenytoin and atropine.
- Acute toxicity due to ingestion may be treated by stomach emptying and repeated use of activated charcoal.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at
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