Heart failure, also called cardiomyopathy, is common in large breeds of dogs but can also occur in smaller breeds. Heart failure occurs when the four chambers of a dog's heart are no longer able to pump sufficient blood throughout the body. Several medications can help the dog live a longer, more active life after a diagnosis of heart failure.
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Positive Inotropic Agents
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Veterinarian Dr. Ron Hines says that one of the oldest drugs used for a dog with a diagnosis of heart failure is a three-drug mixture called digitalis. Digitalis combines Digoxin, Cardoxin, and Lanoxin, drugs called positive inotropic agents. These drugs increase the concentration of calcium in heart muscle cells, which increase the force of heart contractions.
Washington State University College of Veterinary Medicine's website, Vetmed.com, says that the toxic effects of the drug can be serious. Dosing must be precise and monitored, preferably by taking a blood sample eight to 10 hours after a dose of the drug has been given. If the dog already takes certain drugs or has reduced kidney function, dehydration, loss of lean muscle mass or low blood potassium levels, the risk of toxicity is increased.
Adverse side effects can include heart rhythm disturbances, loss of appetite, vomiting, diarrhea and depression.
Diuretics
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Many dogs with heart failure respond well to diuretics, also called "water pills." The most common diuretic prescribed for dogs is furosemide, sold under the brand name Lasix or Disal.
Diuretics help dogs eliminate excess fluid that can accumulate around the lungs, heart and abdomen because of sluggish blood flow. Dogs may initially do well on diuretics only but, as the heart deteriorates, may need additional medication.
Diuretics cause dogs to drink and urinate more. Dogs taking diuretics should be let out more frequently to prevent accidents. Dr. Hines suggests monitoring potassium level in dogs taking diuretics.
Side effects of diuretics mainly include symptoms related to excess fluid loss, which may result in dehydration and weakness.
ACE Inhibitors
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Vetmed.com says that angiotensin converting enzyme (ACE) inhibitors may be the only drug a dog needs early in the disease. These drugs dilate blood vessels and moderate excess hormone activity that occurs with heart failure, which reduces resistance in blood vessels, allowing blood to flow more freely. ACE inhibitors include enalapril (Enacard, Vasotec), benazepril (Lotensin) and lisinopril (Prinivil, Zestril).
Side effects of these drugs can include vomiting or diarrhea, deterioration of kidney function, elevation of blood potassium levels or low blood pressure. Dr. Hines suggests having the dog's kidney function monitored while taking ACE inhibitors.
Other Medicines
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The National Center for Biotechnology Information says beta blockers can be used for dogs with heart failure. Other drugs that may be effective include calcium channel blockers and nitroglycerine.
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