By Kayla Hyland, DVM; Rania Gollakner, BS, DVM, MPH

What is atenolol?

Atenolol (brand name: Tenormin®) is a beta-blocker heart medication used to treat certain types of heart disease, high blood pressure, and abnormal heart rhythms in dogs, cats, and ferrets.

Its use in cats, dogs, or ferrets to treat heart diseases is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and caution very carefully as they may be significantly different from those on the label.

How is atenolol given?

Atenolol is given by mouth in the form of a tablet or a compounded liquid. It may be given with or without food. If vomiting or nausea occur after dosing on an empty stomach, give future doses with food or a treat. For the medication to be effective, it must be given exactly as prescribed, with no missed doses. Do not stop this medication abruptly; slowly taper to avoid adverse reactions.

This medication should take effect within 1 to 2 hours; however, effects may not be noticeable and therefore laboratory tests may be needed to evaluate this medication’s effectiveness.

What if I miss giving my pet the medication?

Give the missed dose as soon as you remember, and then wait the recommended amount of time between doses. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effects of atenolol include tiredness, vomiting, and/or diarrhea. Adverse side effects typically occur in geriatric pets or those with severe heart disease, and include low heart rate, low appetite, lethargy, depression, worsening heart failure, low blood pressure, low blood sugar, cough, collapse, and difficulty breathing.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Atenolol should not be used in pets that are hypersensitive to this class of medications. It should not be used in patients in heart failure, with heart block greater than the first-degree, low heart rates, or bronchospastic lung disease. Atenolol should not be used in cats with left-sided heart failure due to hypertrophic cardiomyopathy (HCM).

It should be used with caution in pets with significant kidney disease, diabetes, asthma, certain heart conditions, or a history of gastrointestinal ulcers. Dogs with certain ADRB1 genes are more sensitive to the effects of this medication. Atenolol should be used with caution in pregnant or lactating animals, and the benefits of use should outweigh the risks.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with atenolol: alpha-1 blockers, amiodarone, ampicillin, anesthetics, calcium antacids, antidiabetic agents, baclofen, bethanechol, bromocriptine, buprenorphine, buspirone, butorphanol, diazepam, diazoxide, diphenhydramine, doxepin, cabergoline, calcium-channel blockers, clonidine, corticosteroids, digoxin, disopyramide, dobutamine, dopamine, dolasetron, hydralazine, glucagon, loop diuretics, methimazole/carbimazole, NSAIDs, phenothiazines, reserpine, sympathomimetics, warfarin, and yohimbine.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Cardiac function, heart rate, heart rhythms, and blood pressure may need to be monitored while using this medication. Pets should be monitored at home for adverse side effects.

How do I store atenolol?

Atenolol tablets should be stored at room temperature away from light, heat, and moisture. Liquid compounded medications should be stored according to the label.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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