Heartworms are parasites that swim in the bloodstream as juveniles and live in the heart as adults. As the juveniles mature, they transfer to mosquitoes that feed off of the infected dog, where they live temporarily until that mosquito bites another dog. The juveniles then transfer to the new dog, where they migrate to the heart and mature into six-inch long adults. If left untreated, a heartworm infestation can eventually clog the heart and cause death. The most common treatment is a combination of Immiticide and Ivermectin.
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Ivermectin
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The initial phase of heartworm treatment involves killing the juveniles that are circulating in the bloodstream to prevent them from replacing the adults. Ivermectin-based drugs are the most effective microfilaria-killing drugs, and can be given orally or injected. Several Ivermectin injections are generally given before treatment can begin for the adult worms, but newer methods involve administering up to three months worth of an Ivermectin-based heartworm preventative such as Heartgard Plus. The advantages of this method are that the drug is given orally, so owners can do it at home, and the chances of a reaction to the Ivermectin are greatly reduced.
Immiticide
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Immiticide is the only drug that can kill adult heartworms, and is traditionally injected into the muscle along the spine in three separate doses. According to Merial, the drug's manufacturer, full treatment can be achieved in two well-timed doses. Some veterinarians, however, believe that this causes too many worms to die at once, which can lead to system shock.
Benefits
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The main benefit of the two-drug approach is that the disease can be fully eradicated within a month, as opposed to two years for Ivermectin-only treatment. The current accepted protocol also kills the gradually enough to prevent shock, unlike treatment with milbemycin oxime.
Risks
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No heartworm treatment is without risk. These injections are painful, and according to Veterinary Partner, 30 percent of dogs experience some kind of reaction at the injection site. Side effects can include tremors, weakness, lethargy, vomiting and respiratory issues, and should be reported to your vet immediately. Ivermectin should not be given to Collies or Collie mixes, as it can cause fatal reactions.
Alternatives
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Milbemycin oxime (Sentinel) is another monthly heartworm preventative that can be used to kill microfilaria, but it may kill them too quickly. Too many dead parasites floating around in the blood at the same time can cause a type of toxic shock and endanger the dog's life. There are a number of non-prescription herbal heartworm treatments on the market, and although some of them may in fact expel some of the worms, none have been proven to actually cure an infestation.
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