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Metoprolol Tartrate (Lopressor®, Toprol XL®)

By: PetPlace Veterinarians

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  • The autonomic (involuntary) nervous system is divided into the sympathetic (fight or flight 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. 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.
  • The effects of beta-adrenergic receptor stimulation include increasing blood sugar, a faster heart rate, stronger heart contraction and increased oxygen consumption. Often, increased blood pressure also occurs.
  • Other effects of beta-adrenergic receptor stimulation include relaxation of the bronchial tree, which causes the bronchial tubes to dilate. Some blood vessels also dilate.
  • Metoprolol belongs to a general class of drugs known as beta-blockers. Other related drugs in this class include Brevibloc® (esmolol), Tenormin® (atenolol) and Inderal® (propranolol).
  • Metoprolol blocks the beta specific receptors and minimizes these effects.
  • The effects of metoprolol are especially prominent in the heart, although other organs also can be affected. Typical results include a decreased heart rate, decreased amount of oxygen the heart muscle needs and decreased blood pressure.
  • Metoprolol 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

  • This drug is registered for use in humans only.
  • Human formulations: Lopressor® (Geigy), Toprol XL® (Astra) and various generic preparations
  • Veterinary formulations: None

    Uses of Metoprolol

  • The primary use of metoprolol is treatment (and sometimes prevention) of cardiac arrhythmias. Commonly treated heart-rhythm disturbances include atrial fibrillation, atrial flutter, supraventricular tachycardia and premature ventricular complexes (PVCs).
  • Metoprolol reduces cardiac output and lowers high blood pressure (systemic hypertension).
  • Reducing heart rate and strength of heart-muscle contraction can be beneficial to some cats and dogs suffering from a condition called hypertrophic cardiomyopathy, especially when the heart muscle contracts so vigorously it obstructs the path of the blood.
  • Metoprolol is also "cardioprotective," which means it protects the heart muscle from damage in chronic heart muscle disease. This benefit is sometimes used to treat dogs with dilated cardiomyopathy (heart muscle disease).

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, metoprolol can cause side effects in some animals.
  • Metoprolol should not be used in animals with known hypersensitivity or allergy to the drug.
  • Metoprolol may cause some animals to become weak due to a slow heart rate or low blood pressure. Rarely, a pet may faint.
  • Metoprolol should be used with caution in animals with congestive heart failure.
  • Metoprolol may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with metoprolol. Such drugs include furosemide, insulin and calcium channel blockers.
  • If a pet collapses while receiving metoprolol tartrate, contact a veterinarian immediately.

    How Metoprolol Is Supplied

  • Metoprolol is available in 50 mg and 100 mg tablets. Extended release tablets are supplied as 50 mg, 100 mg and 200 mg tablets.
  • Metoprolol tartrate injectable is supplied as 5 mg/ml.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • The typical dose administered to dogs is 5 to 25 mg per dog two to three times daily.
  • The typical dose administered to cats is 1 mg per pound (2 mg/kg) once daily. The total daily dose in cats is often 2 to 15 mg per cat three times daily. It is very difficult to accurately dose cats, and this drug is seldom used in this species.
  • Frequently, metoprolol 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.

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