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How to Treat Heartworms in Dogs

4 min read

If not treated properly, heartworms in dogs can cause serious health complications. Learn more about the symptoms and treatment options for dogs with heartworms.


Treatment Options    


  • Medications: Dogs are generally treated with three injections of a drug called melarsomine to kill adult heartworms, a heartworm preventative to kill juvenile heartworms, and doxycycline and prednisone to reduce the chances of unwanted side effects. In some cases, other medications may be prescribed or different protocols recommended.
  • Surgery: Severe cases of heartworms may require surgery to remove the worms from the heart and vessels within the lungs.
  • Exercise Restriction: Exercise restriction is a vital part of successful treatment for heartworms.


What to Expect at the Vet’s Office


If your pet has been diagnosed with heartworm disease via a heartworm antigen test (the most common form of testing), this is what you can expect to happen next at your veterinarian’s office.

  • A test for microfilariae (juvenile heartworms in the blood stream). If no microfilariae are found, a confirmatory test for adult heartworms should be run.
  • Complete blood cell count, blood chemistry tests, a urinalysis, and chest x-rays to assess your dog’s overall condition and plan the safest way to move forward with treatment.
  • Other tests may also be necessary based on a dog’s individual case.


Treatment protocols for heartworms are determined on a case by case basis, but most dogs are treated with some variation of the following:

  • Begin exercise restriction.
  • If the dog’s condition is especially severe, appropriate stabilization therapy is necessary.
  • Begin treatment with prednisone to reduce the chances of a bad reaction to the death of heartworms.
  • Hospitalize the dog for the day and give a heartworm preventative to kill juvenile heartworms in the blood stream. Continue to give heartworm preventatives monthly.
  • Give doxycycline for one month to reduce the chances of a bad reaction to the death of the heartworms.
  • Give the first injection of melarsomine. Restrict exercise, continue prednisone, and closely monitor for side effects for the next 30 days.
  • Give second injection of melarsomine 30 days after first.
  • Give third injection of melarsomine one day after second. Continue prednisone and monitor for side effects for next 30 days.
  • Continue exercise restriction for another 6-8 weeks.
  • Test for microfilariae (juvenile heartworms in the blood stream) approximately one month after third melarsomine injection.
  • Test for adult heartworms and microfilariae approximately 6 months after third melarsomine injection.


 What to Expect at Home


The most important aspect of home care for dogs undergoing treatment for heartworms is exercise restriction. Dogs should be crated when a responsible adult is not able to prevent excess activity. Dogs should only be allowed outside for short leash walks to urinate and defecate. Give your dog the full course of any medications that have been prescribed even if he or she appears to be healthy.


Questions to Ask Your Veterinarian


As with any type of laboratory test, false positive and false negative results on heartworm tests are possible. In particular, dogs who have been bitten by a heartworm infected mosquito within the last 6 months often appear negative on heartworm tests. Retesting at an appropriate date will usually reveal that the dog does have heartworms. If you have any doubts as to your dog’s diagnosis, you can ask that your dog be tested for heartworm disease at a later date or using a different type of test.


Dogs who have had heartworms are not immune to reinfection.  Ask your veterinarian what schedule of testing and preventative administration is required to avoid future heartworm infections.


Possible Complications to Watch for with Heartworms


Side effects are common with heartworm treatment. Many dogs experience soreness and swelling at the site of melarsomine injections (the muscles on either side of the spine). Abscess can also form in these locations. Talk to your veterinarian if your dog is very uncomfortable or her condition appears to be worsening over time.


The most severe problems that are seen after heartworm treatment are related to the sudden death of large numbers of worms. Call your veterinarian immediately if you notice any of the following:

  • your dog develops a cough or a preexisting cough becomes worse
  • your dog has difficulty breathing or pants excessively
  • your dog becomes weak, lethargic, or collapses
  • your dog’s appetite significantly decreases
  • your dog begins to vomit, drool excessively, or develops diarrhea


Authored by Jennifer Coates, DVM


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