Atenolol (Tenormin®) for Dogs and Cats

Overview of Atenolol (Tenormin®) for Dogs and Cats

• Atenolol, also known by the brand name Tenormin®, is a cardiac (heart) drug used in dogs and cats to control their heart rate, lower blood pressure and control rhythm disturbances of the heart in dogs and cats. It does this by blocking certain nervous system impulses (adrenaline and noradrenaline) on the heart.
• The autonomic (involuntary) nervous system is divided into the sympathetic (flight or fight response) and parasympathetic branches.
• Sympathetic activity is communicated to tissues through involuntary (autonomic) nerve impulses and through the blood.
• Cells contain targets, called receptors, which are stimulated by chemicals released from nerves or glands. In the sympathetic system, the chemical transmitter released by nerves is called norepinephrine (noradrenaline). The transmitter chemical released by the adrenal glands is called epinephrine or adrenaline. The receptors for these chemicals are the alpha and beta-adrenergic receptors.
• Atenolol is specific for blocking the beta receptors.
• The effects of beta-adrenergic receptor stimulation that are blocked by atenolol include an increase in blood sugar and a faster heart rate, stronger heart contraction and increase in oxygen consumption. This often results in an increase in blood pressure.
• Atenolol belongs to a general class of drugs known as beta-blocking drugs. Other related drugs in this class include esmolol (Brevibloc®), metoprolol (Lopressor®) and propranolol hydrochloride (Inderal®). These drugs block or reduce the above effects of beta-receptor stimulation. The effects of beta-blockers are especially prominent in the heart though other organs also can be affected.
• Atenolol and other beta-blockers control the heart rate, lower blood pressure and suppress abnormal cardiac rhythms.
• Atenolol is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
• This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

Brand Names and Other Names of Atenolol

• This drug is registered for use in humans only.
• Human formulations: Tenormin® (ICI) and generic preparations (injection and oral tablets)
• Veterinary formulations: None

Uses of Atenolol for Dogs and Cats

• The primary use of beta-adrenergic blockers in animals is treatment (and sometimes prevention) of cardiac arrhythmias. Commonly treated heart rhythm disturbances are atrial fibrillation, supraventricular tachycardia and premature ventricular complexes or PVCs.
• Atenolol reduces cardiac output and therefore lowers high blood pressure.
• Reducing the heart rate and strength of heart muscle contraction can be beneficial to some cats and dogs with the condition called hypertrophic cardiomyopathy, especially when the heart muscle contracts so vigorously it obstructs the path of blood.
• Atenolol can be used in the management of an overactive thyroid gland (hyperthyroidism) in cats, in which excess thyroid hormone adversely affects the heart.

Precautions and Side Effects

• While generally safe and effective when prescribed by a veterinarian, atenolol can cause side effects in some animals.
• Atenolol should not be used in animals with known hypersensitivity or allergy to the drug.
• Atenolol may cause some animals to become weak due to a slow heart rate or low blood pressure. Rarely, a pet may faint.
• Atenolol can depress heart muscle function and heart rate reducing cardiac output. This can be a problem in animals with congestive heart failure and requires very careful dosing.
• If a pet collapses while receiving atenolol, contact a veterinarian immediately.
• Atenolol may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with atenolol. Such drugs include phenylpropanolamine (PPA), often used for urinary incontinence, and drugs used to treat asthma.

How Atenolol Is Supplied

• Atenolol is available in 25 mg, 50 mg and 100 mg tablets.
• Atenolol injectable is supplied as 5 mg/ml.

Dosing Information of Atenolol for Dogs and Cats

• Medication should never be administered without first consulting your veterinarian.
• The typical dose administered to dogs is 0.125 to 0.5 mg per pound (0.25 to 1.0 mg/kg) once to twice daily. The total daily dose is often 6.25 to 25 mg/dog.
• The typical dose administered to cats is 1 mg per pound (2 mg/kg) once daily. The total daily dose in cats is often 6.25 to 12.5 mg once or twice daily.
• Frequently, atenolol is given with other drugs, especially in pets undergoing treatment for heart failure or arrhythmias (abnormal heart rhythm). In these situations, a lower initial dose may be prescribed.
• The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.