Heartworm disease is a parasitic infection generally found in dogs that involves the circulatory system. Dogs are infected with heartworm larvae through the bite of an infected mosquito, the intermediate host. The larvae mature as they travel through the circulatory system, ultimately taking up residence in the heart, where they will remain through the rest of their lives. Heartworm infection causes chronic heart disease and acute cardiac arrest in some dogs. Dogs are routinely treated with oral ivermectin once per month to prevent infection; however using this drug on heartworm-infected dogs can cause a fatal reaction.
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What is Immiticide
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Melarsomine, otherwise known as Immiticide, is a drug used to treat heartworm disease in dogs. It is the only drug currently approved by the FDA for treating heartworm in dogs. A vet will give Immiticide as a deep intramuscular injection into the lumbar muscles. It only kills the adult heartworms in the infected dog. It has no effect on the immature larvae.
History
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Immiticide is an arsenic-based drug. Earlier heartworm treatment protocols involved the administration of intravenous arsenic to dogs over the course of several days to a week. The problem with this treatment is that not only was it toxic to the worms, it was toxic to the infected dogs. Immiticide is a safer drug and does not result in toxicosis like its predecessor. Immiticide is only approved for use in dogs. No human or other companion animal uses are approved either as on or off label.
Side Effects
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While Immiticide is extremely effective and considered safe, it does have side effects. The most common side effect involves the formation of thromboemboli due to dead worms traveling through the circulatory system. The heavier the worm burden, the larger the risk of embolus. Other, less serious side effects include pain and swelling at the injection sites, coughing, lethargy, fever and lack of appetite, though all but the pain and swelling may be attributable to the killing of the worms themselves.
Treatment Protocol
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Immiticide is usually given as a two-injection treatment with the second injection following 24 hours after the first. In dogs with heavy infestations, the vet will give an initial injection followed by the routine two-injection protocol in 30 days.
After Treatment Care
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The vet will keep dogs treated with Immiticide under observation and strict cage rest during the first few days of treatment to reduce the risk of embolus. After release, you should severely restrict the dog's exercise and movement for several weeks following treatment. Veterinarians will routinely give dogs oral ivermectin to kill circulating larvae and place them on monthly heartworm preventative for the rest of their lives.
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