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Atenolol for veterinary use

by Barbara Forney, VMD

Basic Information

Atenolol is a beta adrenergic blocker that is used in veterinary medicine to treat supraventricular tachyarrhythmia, premature ventricular contractions (PVC’s), and systemic hypertension. Beta blockers improve cardiac performance indirectly by reducing the heart rate; prolonging diastole, which allows more time for ventricular and coronary arterial filling.

The effects of atenolol on the cardiovascular system include decreased sinus heart-rate, slowed AV conduction, decreased cardiac output and oxygen demand, and decreased blood pressure. Beta-blockers may be cardioprotective in early cases of hypertrophic cardiomyopathy because they reduce myocardial oxygen demand. Atenolol is most commonly used with other cardiac anti-arrhythmic drugs. The bioavailability of atenolol is higher in dogs (80%) and cats (90%) than in humans. Atenolol undergoes minimal hepatic metabolism and is eliminated in the urine and to a lesser extent in the feces.

Dogs and cats

Dogs: Atenolol is used in dogs to treat arrhythmias, hypertension, obstructive heart disease, subvalvular aortic stenosis, and pulmonic stenosis. Atenolol may be used with other drugs, such as calcium channel blockers and ACEI drugs, in the treatment of systemic hypertension. When atenolol is used to treat atrial fibrillation in dogs, it is frequently used with digoxin.

Cats: Atenolol is used in cats to treat hypertrophic cardiomyopathy (HCM), left ventricular outflow tract obstruction, and hypertension secondary to hyperthyroidism.

  • When beta blockers are used to treat HCM, they are not started until after the cat has been stabilized with diuretics. Some veterinarians will use atenolol as a first-line drug for cats with HCM when they are asymptomatic and early in the disease process.
  • Atenolol is used in cats to treat left ventricular outflow tract obstruction. It is superior to diltiazem in terms of both its side effect profile and its ability to slow the heart rate, which reduces obstruction and decreases murmurs.
  • Atenolol is used to treat cats with hypertension secondary to hyperthyroidism. It may be given during the initial therapy with methimazole. Other forms of hyperthyroidism in the cat may not be as responsive to atenolol.

Side Effects

  • Side effects occur more frequently in older animals and those that are unstable due to cardiac disease.
  • The most common side effects include bradycardia, conduction disturbances, hypotension, depression, loss of appetite, and diarrhea.


  • Beta blockers such as atenolol should not be used in animals that are hypotensive or bradycardic. They should not be used in animals with peripheral vascular disease or arterial thromboembolism.
  • Beta blockers, such as atenolol, should not be used in patients with congestive heart failure until the animal is stabilized (usually with diuretics and ACEI’s).
  • Beta blockers should be used with additional caution in animals with sinus node dysfunction, renal dysfunction, and diabetes.
  • Older cats, particularly those with renal problems, may need additional monitoring.
  • Atenolol therapy should not be started prior to surgery due to potential drug interactions with anesthetic agents.
  • Atenolol crosses the placenta and is found in maternal milk.
  • Therapy with atenolol or other beta blockers should not be withdrawn abruptly. The dose should be tapered gradually.

Drug Interactions

  • Atenolol may block the effects of sympathomimetic drugs, such as metaproterenol, terbutaline, epinephrine, and phenylpropanolamine. These drugs may also decrease the effects of atenolol. Atenolol inhibits isoproterenol induced tachycardia.
  • Anesthetic drugs that depress myocardial function may have an additive effect when used with atenolol.
  • Atenolol may increase the hypotensive properties of drugs such as phenothiazines and reserpine. Drugs such as furosemide and hydralazine may increase the hypotensive potential of atenolol.
  • Concurrent use of atenolol and clonidine may increase the likelihood of rebound hypertension when clonidine therapy is discontinued.


  • Clinical signs associated with overdose are based on the drug’s cardiodepressant effects. These include bradycardia, changes in conduction or rhythm, hypotension, lethargy, and coma. Monitoring and support of cardiovascular status should be instituted. Fluids and presser agents may be necessary.
  • If oral overdose is recognized promptly and the animal is conscious and stable, GI emptying protocols should be instituted and activated charcoal should be administered.
The information contained on this site is general in nature and is intended for use as an informational aid. It does not cover all possible uses, actions, precautions, side effects, or interactions of the products shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular product. You should consult your doctor about diagnosis and treatment of any health problems. Information and statements have not been evaluated by the Food and Drug Administration ("FDA"), nor has the FDA approved the products to diagnose, cure or prevent disease.

Wedgewood Pharmacy compounded veterinary preparations are not intended for use in food and food-producing animals.
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Therapeutic Class
Beta Adrenergic Blocker

Dogs and cats

May Be Prescribed by Veterinarians for:
Cardiac arrhythmias and hypertension

FDA Status
Atenolol is commercially available as Tenormin® (25mg/50mg/100mg tablets)

Search for Available Dosage Forms

About the Author

Barbara Forney, VMD

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.