Call Us
1 800 334-1583

0
X
  • No products in the list
0
LET'S TALK

Heartworm Treatment for Dogs: Side Effects, Care Tips, and Success Rates

Dog Heartworm Treatment

Heartworm disease can be identified during routine health check-ups—such as when a heartworm test is conducted during a dog’s annual veterinary wellness exam—or based on clinical suspicion. No matter how heartworm disease is diagnosed, timely treatment is crucial.

Aims of Heartworm Treatment

Pet owners and veterinarians must understand the objectives of heartworm treatment. While many dog owners consistently administer heartworm prevention, a significant number of dogs still develop the disease due to missed treatments.

When adult heartworms lodge in the pulmonary vessels, they cause considerable inflammation in the vessel walls and surrounding tissues. This results in the clinical signs of heartworm disease, including coughing, exercise intolerance, fainting, abnormal heart and lung sounds, ascites, and other symptoms.

The main goals of heartworm treatment are to alleviate the clinical signs of the disease and to eliminate all heartworms—adults, juveniles, larvae, and microfilariae—from the body.

While live heartworms cause substantial inflammation, the death of these worms can lead to even greater damage. Consequently, treating heartworms doesn’t provide an immediate reduction in risk or resolution of inflammation. In fact, dogs may experience an increased risk of clinical signs as heartworms die, whether due to adulticide treatment or the natural end of their life cycle.

Early treatment with an adulticide helps prevent further damage and facilitates a quicker resolution of clinical signs.

Preventing Complications: Heartworm Diagnostics Before Treatment

Before starting treatment for heartworm disease, it’s essential to conduct diagnostics to evaluate the patient’s health. These tests help both the veterinarian and pet owner prepare for potential complications during treatment and identify strategies to minimize these risks.

Pre-treatment thoracic radiographs are typically advised for dogs with heartworm disease. Expertise in diagnostic imaging and proper positioning on the veterinary table are crucial for accurately assessing the extent of pulmonary damage and predicting the likelihood of treatment-related complications.

Additionally, blood tests, including a complete blood cell count and serum biochemistry, are often recommended prior to treatment. These tests can help identify uncommon complications of heartworm disease, such as liver and kidney damage, while also providing insight into the dog’s overall health status.

Side Effects of Adulticide Treatment

Adult heartworms are treated using melarsomine dihydrochloride, which is administered via intramuscular injection deep into the epaxial muscles.

Melarsomine injections can lead to localized swelling and soreness at the injection site, with severity ranging from mild to severe based on the individual patient. Many dogs benefit from receiving pain medication alongside their melarsomine injections.

A more significant side effect associated with melarsomine treatment is pulmonary thromboembolism. As the adult worms die, they can dislodge and travel into the distal pulmonary arteries, where they are processed by the immune system. While some degree of pulmonary thromboembolism is nearly inevitable with adulticide therapy, not all dogs will exhibit clinical signs.

To minimize clinical signs, it’s essential for owners to strictly limit their pet’s activity during and after treatment, which can help reduce the extent of pulmonary thromboembolism.

Heartworm Treatment Protocol: Melarsomine Dosage and Supportive Medications

Melarsomine label recommendations outline two treatment protocols: a two-dose and a three-dose option.

The manufacturer advises 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 dogs with Class 3 (severe) heartworm disease, which may present with symptoms like coughing, dyspnea, muscle wasting, or fatigue.

However, the American Heartworm Society suggests that all infected dogs should receive the three-dose protocol. The two-dose method only eliminates about 90% of adult worms, while the three-dose protocol is effective against 98% of them. Furthermore, the three-dose approach carries a lower risk of complications related to pulmonary thromboembolism compared to the two-dose protocol.

In addition to melarsomine, several adjunct medications are recommended for dogs undergoing heartworm treatment. These medications enhance treatment efficacy and help minimize side effects:

Steroids

Anti-inflammatory doses of steroids can help reduce clinical signs associated with pulmonary thromboembolism.

Doxycycline

This antibiotic targets Wolbachia, a symbiotic bacterium present in heartworms. Doxycycline is believed to decrease pulmonary inflammation and increase the susceptibility of adult heartworms to adulticide therapy.

Macrocyclic lactones

These medications target microfilariae and third- and fourth-stage larvae. Because melarsomine does not affect larvae and young adults, macrocyclic lactones should be given for two months before adulticide therapy to ensure all heartworms are mature enough to respond to treatment.

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

Vet-Tables Electric Surgery Table with Dental Top

Timeline for Dog Heartworm Treatment

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. Administer first melarsomine injection (2.5 mg/kg IM). Consider pain medication for injection. Begin prednisone (four-week taper, starting at 0.5 mg/kg BID for the first week).

Day 90: Owner administers heartworm prevention at home. Administer second melarsomine injection (2.5 mg/kg IM). Consider pain medication for injection. Repeat four-week prednisone taper.

Day 91: Administer third melarsomine injection (2.5 mg/kg IM).
Continue year-round monthly heartworm prevention and perform follow-up as recommended.

The ‘Slow-Kill’ Heartworm Treatment Method: Cost-Effective but Risky

The “slow-kill” method has been utilized for heartworm cases that cannot undergo adulticidal treatment, often due to financial limitations. In this approach, monthly heartworm prevention (macrocyclic lactones) is started without administering adulticide.

While some see “slow-kill” as an alternative to adulticidal therapy, it’s essential for clients to understand that it is more of a salvage procedure than a true treatment. This method can take over a year for a dog to clear its heartworm infection, and activity must be restricted throughout this entire period, as there’s no way to predict when adult worms will die.

Research indicates that dogs undergoing the “slow-kill” method show radiographic progression of disease similar to those receiving no treatment at all. Furthermore, dogs treated with the “slow-kill” method face a higher risk of pulmonary thromboembolism compared to those receiving adulticidal treatment.

Post-Treatment Monitoring and Aftercare

Clients should be made aware of the risk of pulmonary thromboembolism during and after heartworm treatment. Dogs should have their activity restricted before, during, and for two months following treatment, as activity levels are significant predictors of complications related to adulticidal treatment.

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

Recommended follow-up includes a microfilaria test one month post-treatment and a heartworm antigen test along with a microfilaria test nine months post-treatment.

Prognosis: Success Rates of Heartworm Treatment

With the three-dose adulticide protocol outlined above, along with doxycycline and macrocyclic lactones as recommended by the American Heartworm Society, 98% of dogs will clear their heartworm infection.

If a heartworm antigen test is positive nine months post-treatment and the client has been administering heartworm prevention as directed, treatment failure may be suspected. In such cases, the patient should be treated with doxycycline, followed by two doses of adulticide administered 24 hours apart. The dog should then be retested with a heartworm antigen test nine months later.

Recommended follow-up includes a microfilaria test one month post-treatment and a heartworm antigen test along with a microfilaria test nine months post-treatment.

Key Takeaways

While heartworm treatment carries a notable risk of side effects, these risks can be reduced through early intervention and proper client education. Restricting activity is the most crucial aftercare guideline for dog owners to follow.

References and Further Reading

Catherine Barnette, DVM

Catherine Barnette, DVM is a graduate of the University of Florida College of Veterinary Medicine. She began her career in small animal general practice and spent fourteen years working in a variety of corporate and privately-owned veterinary hosptals. For the last four years, Dr. Barnette has focused her professional energies on creating educational content for veterinary teams and pet owners. She lives in Florida with her husband, daughter, and their menagerie of pets. Dr. Barnette is also a freelance veterinary medical writer, creating informational content for veterinarians, veterinary technology students, and pet owners. She lives in North Carolina with her husband, daughter, and their menagerie of pets.

See all posts