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Heartworm Treatment in Dogs & Common Side Effects

Heartworm Treatment in Dogs & Common Side Effects

Heartworm disease is a serious condition that can lead to irreparable organ damage in dogs.  In this article, staff at Carolina Veterinary Specialists explain what pet owners should be prepared for during their dog's heartworm treatment.

What is heartworm disease?

Heartworm is spread through the bite of an infected mosquito, which can pass a parasitic worm called dirofilaria immitis into a dog's bloodstream. Heartworm is not contagious, and cannot be passed from one host dog to another, it is only through Mosquito bites that heartworm passes. Do not make the mistake of thinking that means the risk of heartworm is low; heartworm has been reported in all 50 states while being especially common between New Jersey and the Gulf of Mexico, as well as along the Mississippi River and its major tributaries.

If your pet is bitten by an infected mosquito, the worms will mature into adults, mate, and produce offspring while living inside your pet's heart, lungs, and blood vessels.

What is heartworm treatment in dogs?

The team at Carolina Veterinary Specialists cannot stress enough that, when it comes to heartworm, prevention is vastly superior to treatment.  We recommend contacting your vet post-haste to formulate a preventative treatment plan for your canine companion if you have not already.  Most commonly Heartworm prevention is administered through a monthly medication that can be prescribed by your vet.   

In the cases Where preventative measures fail to prevent infection, there are treatment options available for your pet, though all come with the possibility for serious side effects and health complications, though fatalities are rare.

Because Heartworm is undetectable until at least 5 months after infection, many dogs are suffering from advanced Heartworm Disease by the time they are diagnosed, requiring swift and intense treatment.  In rare cases, the damage to the dog's internal organs may be so severe by the time the condition is detected that it is better to treat the damage and keep the patient comfortable rather than assume the additional risks associated with attempting to kill the heartworms.  Dogs in this advanced condition have a life expectancy of only a few weeks or months. 

Thankfully, a new medication has been developed for killing adult heartworms while having fewer dangerous side effects.  Melarsomine is an injectable drug that kills adult heartworms that is administered over the course of multiple injections.  Typically your dog will be given a 30 day rest period after their first injection, after which they will receive two more injections 24 hours apart.  Antibiotics will also be prescribed to combat any infectious bacteria the heartworms may be carrying.  With this new medication, 95% of dogs with heartworms are now able to be successfully treated.

Your dog will also receive treatment to kill juvenile heartworms (microfilaria) either before or after their Melarsomine treatment.  Your dog may need to spend the night in the hospital for observation on the day this treatment is administered.

What should I do after my dog's heartworm treatment?

It is critical that your dog be allowed to rest following their injection.  Heartworm treatment in dogs kills the Adult heartworms within a few days, but further complications can occur while their corpses are decomposing.  It can take several months for the heartworms to be reabsorbed into the patient's bloodstream.  Most post-treatment complications arise from these fragments of decomposing heartworms, so to minimize this risk your dog must not be allowed to exercise and should be kept as quiet as possible for the first month following treatment.  For seven to eight weeks following injection, a cough will be noticeable.  If this cough persists beyond this or is especially severe, as well as if your dog is demonstrating shortness of breath or fever, contact your veterinarian right away.

What are the side effects of heartworm treatment in dogs?

Treatment for heartworm can cause serious complications for your pet's health and can be potentially toxic to the dog’s body.  Many dogs experience soreness and swelling at the site of their injections.  The most severe side effects are related to a large number of worms suddenly dying.  You must contact your vet immediately if your dog is panting excessively, has difficulty breathing, is suddenly lethargic or collapses, begins to reject food, begins to vomit, or develops diarrhea.


Our Hospital is open 24/7 for emergency visits. If you suspect your dog is suffering from heartworms, or side effects from heartworm treatments, contact us right away. We will work with your primary Veterinarian to ensure the best treatment for your valued pet.

Caring for Pets in Matthews

Carolina Veterinary Specialists in Matthews accepts new clients to our specialty services by referral only. Our emergency service accepts all clients.

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