Dog behavior after heartworm treatment

Heartworm disease is a serious health issue for dogs, as it can cause permanent damage to the lungs, heart and other organs. Thankfully, this condition can be treated with medication and careful monitoring. While treatment is usually successful in bringing a dog back to full health, owners may notice changes in their pet’s behavior after the completion of treatment. From increased shyness to changes in energy levels, it is important for owners to understand the impact of heartworm treatment on their canine companion. The treatment of canine heartworm is an important step in caring for your pet’s health and well-being. It can be a worrying time for pet owners, as the process can have a big effect on their beloved furry friend. After treatment, however, it is important to monitor your dog’s behavior to ensure that they are adjusting well. This article will explore the behavioral changes that may occur after heartworm treatment in dogs, along with possible ways to help them through this transition period.

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 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.

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.

What to expect after heartworm treatment

Once your dog has finished his heartworm treatment’ you should expect him to be bedridden for a while.

“Only slow, low-impact walks are allowed for the first five to six months after diagnosis,” Dr. Marteney told The Dodo. “No running, jumping, playing or high-impact exercise as these activities may cause the worms to break loose and cause significant harm to the pet being treated.”

In order to keep your dog from doing any of these things, you’re going to need some prescription medication that’ll make him more mellow than he’s ever been before.

“Many dogs require sedative medications to achieve this level of calm in addition to the other medications for heartworm disease”.

How long after heartworm treatment can my dog be active?

Your dog won’t be able to be active after his heartworm treatment for at least a few months.

“The dead heartworms take some time to be broken down by the dog’s immune system”.

If the dead worms are still intact, they can cause major issues if your dog’s heart rate becomes elevated.

“If a dog exercises too early, the increased blood flow from the heart beating faster could push one of the worm carcasses deeper into the vessels of the lungs”.

This is super serious — and even life-threatening — because the dead worms could block the blood flow to your pup’s lungs.

Goals of heartworm treatment

Pet owners and veterinarians should have a clear understanding of the goals of heartworm treatment. While many dog owners administer heartworm prevention on a regular basis, too many dogs do not receive these treatments and eventually develop the disease.

When adult heartworms become lodged within the pulmonary vessels, they cause significant inflammation within the vessel walls and surrounding tissues. This leads to the clinical signs associated with heartworm disease: coughing, exercise intolerance, syncope, abnormal heart and lung sounds, ascites, and a host of other symptoms.

The primary goals of heartworm treatment are to minimize the clinical signs associated with heartworm disease and to eliminate all heartworms (adults, juveniles, larvae, and microfilariae) from the body.

While live worms cause significant inflammation in the pulmonary vessels, dying and dead worms can result in even more damage. As such, treating heartworms does not result in an immediate risk reduction or the immediate resolution of inflammation. In fact, dogs are often at a higher risk of clinical signs of heartworm disease as heartworms die, regardless of whether the parasite’s death is caused by adulticide treatment or the natural end of the life cycle.

Treating heartworms early, using an adulticide, prevents worsening damage and leads to faster resolution of clinical signs.

Avoiding complications: pre-treatment heartworm diagnostics

Prior to beginning treatment for heartworm disease, diagnostics should be performed to assess the patient’s health status. These diagnostics can better prepare the veterinarian and pet owner for complications that may arise during treatment and suggest approaches to minimize these risks.

Pre-treatment thoracic radiographs are often recommended for patients with heartworm disease. A technical proficiency in diagnostic image and proper positioning on the vet table are paramount in assessing the degree of pulmonary damage and predicting the likelihood of treatment-related complications.

Bloodwork, including a complete blood cell count and serum biochemistry, is also often recommended prior to treatment. This can help in assessing for uncommon complications of heartworm disease, such as liver and kidney damage, while also assessing the dog’s overall health status.

Understanding Your Dog’s Post-Heartworm Recovery

Heartworms are one of the most serious parasites that affect dogs. While treatment is available, post-heartworm recovery is still an important process for pet owners to understand. Without proper care and management, the long-term effects can be devastating for your pooch. Recovery from heartworm disease can be lengthy and complex. After treatment, it’s important to keep a close eye on your dog’s health as they may suffer from secondary complications such as pulmonary thromboembolism or congestive heart failure if left untreated. It is also essential to monitor their weight, diet, exercise levels and overall behavior during this time. When in doubt about how best to support your pup during recovery it’s always beneficial to consult with a vet for advice specific to your pet’s needs.

Adulticide treatment side effects

Adult heartworms are treated with dihydrochloride. This medication is administered by intramuscular injection, deep into the epaxial muscles.

Injections are often associated with localized, injection-site swelling and soreness. These local effects may vary from mild to severe, depending on the patient. Many patients benefit from the administration of pain medication in conjunction with their melarsomine injections.

A more significant side effect associated with treatment is pulmonary thromboembolism: dead or dying worms dislodge and travel into distal pulmonary arteries, where they are broken down by the immune system. Some degree of pulmonary thromboembolism is virtually guaranteed with adulticide therapy, but not all dogs will show clinical signs.

Clinical signs can be minimized by ensuring that owners strictly restrict their pet’s activity during and after treatment, which reduces the degree of pulmonary thromboembolism that occurs.

Heartworm treatment protocol: melarsomine dosage and adjunct medications

Melarsomine label recommendations discuss two treatment options: a two-dose protocol and a three-dose protocol.

The manufacturer recommends the two-dose protocol for dogs with Class 1 (asymptomatic or mild) or Class 2 (moderate) heartworm disease. The three-dose protocol is recommended for use in dogs with Class 3 (severe) heartworm disease, including dogs with cough, dyspnea, muscle wasting, and/or fatigue.

In contrast to the manufacturer recommendations, however, the American Heartworm Society recommends that all infected dogs be treated with the three-dose protocol. The two-dose protocol kills only 90% of adult worms (according to label claims), while the three-dose protocol kills 98% of adult worms. Additionally, the three-dose protocol is associated with a lower risk of effects related to pulmonary thromboembolism than the two-dose protocol.

In addition to melarsomine, a number of adjunct medications are recommended in dogs undergoing heartworm treatment. These medications, which help improve treatment efficacy and minimize side effects, include:

  • Steroids

Anti-inflammatory doses of steroids minimize clinical signs associated with pulmonary thromboembolism.

  • Doxycycline

This antibiotic is effective against, a symbiotic bacterium found within heartworms. Doxycycline is thought to decrease pulmonary inflammation while making adult heartworms more susceptible to adulticide therapy.

  • Macrocyclic lactones

These are used to kill microfilariae and 3rd and 4th stage larvae. Because melarsomine is ineffective against heartworm larvae and young adult worms, macrocyclic lactones should be administered for two months prior to adulticide therapy, thus ensuring that all heartworms in the dog are mature enough to be susceptible to melarsomine.

Macrocyclic lactones should be used with caution in dogs with high micro filarial counts, as rapid micro filarial die-off may lead to significant clinical signs.

Dog Heartworm treatment timeline

The treatment timeline recommended by the American Heartworm Society is as follows:

  • Day 0 (diagnosis): Discuss heartworm disease and treatment with the client.

Begin exercise restriction to reduce risk of pulmonary thromboembolism.

Administer prednisone if the dog is symptomatic for heartworm disease.

Begin doxycycline (10 mg/kg PO BID for 4 weeks).

  • Day 1: Administer heartworm prevention in the veterinary clinic, then monitor for 8 hours.

Consider pre-treatment with antihistamines and/or steroids, to reduce reaction risk.

  • Day 30: Owner administers heartworm prevention at home.
  • Day 60: Owner administers heartworm prevention at home.

The “slow-kill” heartworm treatment method: cheaper, but riskier

The “slow-kill” method has long been used in heartworm cases that cannot receive adulticidal treatment, often due to financial constraints. In this treatment, monthly heartworm prevention (macrocyclic lactones) is initiated without adulticidal treatment.

While many view “slow-kill” as an alternative to adulticidal therapy, it is important that clients understand that it is more a salvage procedure than an actual medical treatment. With this treatment, it can take upwards of a year for the dog to clear their heartworm infection. Activity must be restricted throughout that entire time period, since there is no way to predict when adult worms will die.

Studies have shown that dogs treated with the “slow-kill” method show radiographic progression of disease that is indistinguishable from dogs receiving no treatment at all. Additionally, dogs receiving “slow-kill” treatment are at a higher risk of pulmonary thromboembolism than dogs receiving adulticidal treatment.

Aftercare and post-treatment monitoring

Clients should be informed of the risk of pulmonary thromboembolism during and after heartworm treatment. Dogs should have their activity restricted before treatment, during treatment, and for two months after treatment. Activity during or after treatment is one of the most significant predictors of complication associated with adulticidal treatment.

Clients should also be advised to monitor their dog closely for signs of pulmonary thromboembolism. Signs may include coughing, hemoptysis, shortness of breath, weakness/lethargy, or pale mucous membranes. If these signs are observed, the dog should receive immediate veterinary attention.

Prognosis: heartworm treatment success rates

With the three-dose adulticide protocol described above, in conjunction with doxycycline and macrocyclic lactones as recommended by the American Heartworm Society, 98% of dogs will be cleared of heartworm infection.

In the event that a heartworm antigen test is positive at nine months post-treatment and the client has been administering heartworm prevention as directed, treatment failure is suspected. The patient should be treated with doxycycline and then given two doses of adulticide, 24 hours apart, and then be retested with a heartworm antigen test nine months after.


In conclusion, heartworm is a serious condition that affects thousands of dogs each year. Treatment for heartworm can be successful, but there are also potential side effects to consider. Dogs may experience behavioral changes after treatment, including lethargy and reduced activity levels. It is important to monitor your dog’s behavior during this time as these symptoms should improve with time and rest. If the symptoms persist or worsen, it is best to contact your veterinarian for further evaluation and treatment.

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