Heartworm preventative medicines, such as ivermectin, are recommended by the American Heartworm Society to be administered to dogs to help protect against the development of heartworm disease. Caused by bites from mosquitoes carrying the heartworm parasite, heartworm disease can be damaging to the lungs, heart, liver, and kidneys and can even be a potentially fatal health problem.
If a dog does becomes infected with heartworm disease, there are heartworm treatment options available. However, giving dogs products that prevent the condition—by killing the heartworms deposited from infected mosquitoes before they grow into adults—leads to lower health risks. Prevention also carries a lower price tag over the long run. To ensure effectiveness, preventatives like ivermectin should be given year-round, even in areas where temperatures drop below freezing.
What is Ivermectin?
The earliest family of drugs approved to prevent heartworm disease, ivermectin is included in the brand-name products Heartgard and Heartgard Plus (from the manufacturer Merial), Iverhart Plus and Iverhart MAX (from Virbac), and Tri-Heart Plus (from Shering-Plough) and is taken orally. Ivermectin is able to combat the harmful effects of heartworm larvae transmitted via mosquitoes from as far back as two months prior to the first dose of preventative. It is safe to be given to dogs ages six weeks and older.
Intolerance to Ivermectin
Some breeds of dogs, including Collies, Australian Shepherds, Shetland Sheepdogs, Old English Sheepdogs, and English Sheepdogs, may have intolerance to ivermectin. Testing is available to see if your dog may have the genetic mutation making her or him susceptible to a toxic reaction from ivermectin (which could lead to blindness, breathing issues, and even death).
According to Washington State University’s College of Veterinary Medicine’s Veterinary Clinical Pharmacology Lab, the dosage of ivermectin in heartworm products is small enough to be safe for dogs with this genetic mutation. Products administered monthly (versus every six to 12 months) are recommended, though you should consult your vet.
Higher dose drugs (like ones that treat already-present heartworm, or for treating mange, which has 50 times the dose of ivermectin of heartworm prevention products) are at levels that are toxic for dogs with this mutation.
Using Heartworm Preventatives
You should choose a heartworm preventative based on how easily and readily your dog will take the product (some are designed to have added flavors or to be chewable to make offering the dosage easier) and whether the product is also able to protect your pet from fleas, ticks and other parasites.
Before your pet begins taking a preventative treatment, your vet should check for the presence of heartworms—particularly since heartworm disease symptoms (including coughing, fatigue, difficulty breathing, and not wanting to exercise) may not yet be present, may not develop, or may go unnoticed. This is done with a blood test. Your dog should get re-tested for heartworm on an annual basis before continuing to take heartworm prevention products.
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This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.