HEARTGARD for Dogs? Why?

When to Give Heartgard to Dogs

By Rena Sherwood

Heartgard is the brand name of the anti-parasitic medication ivermectin made by Merial. There is also a version called Heartgard Plus, which is a combination of ivermectin and pyrantel. These chewable tablets are given as a preventative to heartworms. According to Merial, they should be given once a month every month, but only if the dog is free of adult heartworms.

Australian Shepard Mix

Heartgard does not kill adult heartworms. Before starting a dog on Heartgard, the dog needs to have a heartworm test. Only melosomine dihydrochloride kills adults.

Function

According to "Dog Owner's Home Veterinary Handbook," heartworm larvae that are in their second and third moults (called the L3 and L4 stages) can be killed by Heartgard. During this time, they live in the dog's bloodstream and not the heart, where Heartgard cannot reach.

Administration

Give one tablet as directed once per month. More than that and the dog will get ill. Because of the meaty flavor, dogs eat it voluntarily.

After Treatment

If a dog has been successfully treated for adult heartworms, "Dog Owner's Home Veterinary Handbook" points out they should not be given Heartguard until 4 or 5 weeks later. This gives the dog's bodies a chance to recover from the strong melosomine dihydrochloride.

Misconception

Dogs can become infected with heartworms over the winter, so Heartgard should be given every month.

Heartworm Disease

Heartworm disease is a serious illness that can rob your dog of its health and even its life.
Heartworm larvae are transmitted by infected mosquitoes that bite the dog and deposit heartworm larvae on the dog's skin. The larvae migrate through the tissue and into the bloodstream of the dog where they continue developing. By the time clinical signs of heartworm disease appear, the disease can already be in its advanced stages.
Heartworms spend their adult lives in the right side of the heart and the large blood vessels that connect the heart to the lungs. The adult worms block the heart and major blood vessels leading from the heart to the lungs, liver, and kidneys and can grow up to 12 inches long.

Why shouldn't I wait and see if my dog develops heartworm disease? Can't my veterinarian just treat it?

It's important to understand that heartworm disease has usually reached an advanced stage by the time your dog shows signs of illness, and it is possible that the dog may never show signs of an infection. Treatment is risky, expensive, and may not be effective. The approved treatment involves the use of a product containing arsenic, your dog will be kept inactive during treatment, and you will have to keep your dog inactive for weeks afterward – and despite these measures, treatment may not be successful.

How does my dog get heartworms?

Heartworms Transmission

A mosquito bites an animal that is already infected and ingests immature heartworms, called microfilariae, circulating in the animal's blood. The mosquito becomes infected. The microfilariae develop to the next stage and become larvae.

An uninfected puppy or adult dog is infected by larvae deposited by a bite from the infected mosquito. The American Heartworm Society reports that virtually 100% of dogs exposed to infective larvae become infected³

In dogs without heartworm protection, the heartworm larvae continue to mature and develop, migrating through the tissues and reaching the heart and pulmonary arteries. Larvae become adult heartworms within 6 months of infection.

Adult heartworms grow up to 12 inches long and reproduce. Infected dogs infect more mosquitoes, which can then infect additional dogs.

IMPORTANT RISK INFORMATION: HEARTGARD is well tolerated. All dogs should be tested for heartworm infection before starting a preventive program. Following the use of HEARTGARD, digestive and neurological side effects have rarely been reported. For more information, contact your veterinarian.