Heartworm Treatment in Dogs & Common Side Effects

Updated: June 3, 2023


Heartworm disease is a potentially life-threatening condition that affects dogs worldwide. It is caused by a parasitic worm called Dirofilaria immitis, which is transmitted through mosquito bites. Heartworms primarily target the heart, lungs, and blood vessels, causing severe damage and compromising the overall health of infected dogs.

Thankfully, there are effective treatment options available to combat heartworm disease in dogs. The treatment typically involves a series of steps aimed at eliminating the adult worms and preventing further infection. However, it is important to note that heartworm treatment can be challenging and may have certain side effects.

The primary objective of heartworm treatment is to kill the adult worms residing in the dog’s heart and pulmonary arteries. This is typically accomplished using a medication called melarsomine dihydrochloride, which is administered through a series of injections. The injections are typically given deep into the dog’s lumbar muscles and are spaced apart to allow for proper recovery and minimize potential complications.

While the treatment itself is effective, it can pose risks and side effects. One common side effect is the development of a “post-treatment inflammatory response,” which occurs as the worms start to die and disintegrate. This response can cause inflammation and clotting in the pulmonary arteries, leading to coughing, lethargy, and breathing difficulties. Additionally, the breakdown of the worms can release toxins into the dog’s bloodstream, potentially causing an adverse reaction.

What is heartworm disease?

Heartworm disease poses a significant threat to dogs worldwide, and its transmission occurs exclusively through the bite of an infected mosquito. This mosquito carries a parasitic worm called Dirofilaria immitis, which enters the dog’s bloodstream during the bite. It is crucial to understand that heartworm is not contagious and cannot be directly transmitted from one dog to another. The sole means of transmission is through the bite of an infected mosquito.

Despite its limited mode of transmission, heartworm disease remains a prevalent concern across the United States. It has been reported in all 50 states, with higher incidences observed in regions spanning from New Jersey to the Gulf of Mexico. Additionally, areas along the Mississippi River and its major tributaries have also exhibited a significant prevalence of heartworm cases.

Once a dog is bitten by an infected mosquito, the heartworm larvae present in the mosquito’s saliva enter the dog’s body. Over time, these larvae mature into adult worms, taking up residence in the dog’s heart, lungs, and blood vessels. Inside these vital organs, the adult worms reproduce and produce offspring, perpetuating the cycle of heartworm infection.

It is essential for dog owners to recognize the severity of heartworm disease and take preventive measures to safeguard their pets. Preventive measures typically involve administering monthly heartworm preventive medications that effectively kill the larvae before they mature into adults. Regular veterinary check-ups and screening tests are also crucial to identify and treat heartworm infection at an early stage.

What is heartworm treatment in dogs?

Prevention of heartworm disease is of utmost importance, as emphasized by the team at Carolina Veterinary Specialists. They strongly advise pet owners to take proactive measures to prevent heartworm infection rather than relying on treatment alone. It is recommended to promptly consult with a veterinarian to develop a preventative treatment plan for your canine companion if you haven’t done so already. The most common method of heartworm prevention is the administration of monthly medication prescribed by a veterinarian.

However, in cases where preventive measures fail to avert infection, treatment options are available, albeit with potential risks and complications. It is important to note that fatalities associated with heartworm treatment are rare, but serious side effects and health complications can occur.

Heartworm Treatment in Dogs

Detecting heartworm disease is challenging as it remains undetectable until at least five months after infection. As a result, many dogs are diagnosed with advanced heartworm disease, necessitating immediate and intensive treatment. In some rare cases, the damage inflicted on the dog’s internal organs is so severe that it may be more beneficial to focus on managing the damage and ensuring the patient’s comfort rather than risking additional complications by attempting to eliminate the heartworms. Dogs in such advanced stages of the disease typically have a limited life expectancy of only a few weeks or months.

Fortunately, a new medication, melarsomine, has been developed to kill adult heartworms with fewer dangerous side effects. This injectable drug is administered through a series of multiple injections. After the first injection, the dog is given a 30-day rest period, followed by two more injections administered 24 hours apart. Antibiotics may also be prescribed to address any potential bacterial infections carried by the heartworms. This new treatment approach has led to a success rate of approximately 95% in treating dogs with heartworm disease.

Heartworm Treatment for Dogs and Cats

When it comes to heartworm treatment for dogs and cats, there are several important considerations to ensure the best possible outcome for your pet. Here are eight tips to guide you through the heartworm treatment process:

Consult with a veterinarian:
The first step in treating heartworm disease is to seek professional advice. A veterinarian will conduct diagnostic tests to confirm the presence of heartworms and recommend the most appropriate treatment plan for your pet’s specific condition.

Strict rest and confinement:
Following treatment, your pet will need to be kept calm and have restricted physical activity. This is to prevent complications such as blood clots and allow for proper healing. Avoid strenuous exercise and keep your pet’s excitement levels in check.

Medications to kill adult worms:
Treatment often involves the administration of medications to eliminate adult heartworms. These medications may be given orally or through injections, depending on the severity of the infection. Follow the prescribed dosage and administration instructions carefully.

Management of side effects:
Some pets may experience side effects during heartworm treatment, such as coughing, lethargy, or appetite loss. Consult with your veterinarian if you notice any unusual symptoms, as they can provide guidance on managing these side effects effectively.

Monitoring and follow-up visits:
Regular follow-up visits are crucial to monitor your pet’s progress and ensure that the treatment is working effectively. Diagnostic tests may be conducted periodically to assess the reduction in heartworm burden and the overall health of your pet.

Addressing complications:
In severe cases, heartworm disease may lead to complications such as heart or lung damage. If your pet has any underlying health issues or develops complications during treatment, your veterinarian will provide appropriate care and treatment options.

Preventive measures:
Once the treatment is completed, it is essential to prevent re-infection. Continue with heartworm preventive medications as recommended by your veterinarian. These medications help protect your pet from future heartworm infections.

Regular check-ups:
Routine veterinary check-ups are vital to monitor your pet’s overall health and ensure that they remain free of heartworm disease. Your veterinarian can advise on the appropriate frequency of check-ups based on your pet’s specific needs.

Prevention is always better than treatment when it comes to heartworm disease. Maintain a regular schedule of heartworm prevention for your pets, as it is the most effective way to safeguard their health.

Heartworm Treatment in Dogs

Home Care During Heartworm Treatment

Home care during heartworm treatment plays a crucial role in supporting your pet’s recovery and ensuring the best possible outcome. Here are some important tips for providing effective home care during heartworm treatment:

Strict rest and confinement:
Following your veterinarian’s instructions, ensure that your pet gets plenty of rest and restrict their physical activity. Avoid activities that may strain their cardiovascular system, such as running, jumping, or playing vigorously. Use a leash when taking your dog outside to prevent excessive movement.

Create a calm and comfortable environment:
Provide a quiet and stress-free environment for your pet to aid in their recovery. Keep them away from loud noises, other pets, and anything that may cause excitement or anxiety.

Medication administration:
Administer any prescribed medications exactly as directed by your veterinarian. Follow the recommended dosage, frequency, and duration of treatment. If you have difficulty giving medications, ask your veterinarian for tips or alternative administration methods.

Monitor for side effects:
Keep a close eye on your pet for any potential side effects of the treatment. This may include coughing, vomiting, diarrhea, or loss of appetite. If you notice any concerning symptoms, contact your veterinarian promptly for guidance.

Preventive measures:
While your pet is undergoing heartworm treatment, it is crucial to continue providing monthly heartworm preventive medications for any remaining heartworm larvae or to prevent new infections. Consult with your veterinarian to determine the most appropriate preventive medication and follow their recommendations.

Good nutrition:
Ensure your pet receives a balanced and nutritious diet during their recovery. Consult with your veterinarian about dietary recommendations that can support their immune system and aid in the healing process.

Regular veterinary check-ups:
Stay on schedule with follow-up visits as recommended by your veterinarian. These visits allow your veterinarian to monitor your pet’s progress, conduct necessary tests, and adjust the treatment plan if needed.

Emotional support:
Provide your pet with comfort, reassurance, and attention during their recovery period. Offer plenty of love, gentle petting, and positive interactions to help alleviate any stress or anxiety they may experience.

Home care during heartworm treatment should always be carried out in close consultation with your veterinarian. They will provide specific instructions based on your pet’s condition and guide you through the recovery process. By following their advice and providing a supportive home environment, you can contribute to your pet’s successful treatment and overall well-being.

Heartworm Treatment in Dogs

Common Side Effects of Heartworm Treatment

Heartworm treatment in dogs is essential to eradicate the parasite and restore their health. However, like any medical intervention, heartworm treatment may come with certain side effects. It is important for pet owners to be aware of these potential side effects and understand how to manage them. Here are some of the common side effects associated with heartworm treatment:

1, Immiticide (Melarsomine) Treatment Side Effects:

  • Injection site reactions: Immiticide is administered through injections, and localized pain, swelling, or inflammation at the injection site may occur.
  • Fever: Some dogs may experience a temporary increase in body temperature following treatment.
  • Lethargy: Dogs undergoing Immiticide treatment may exhibit signs of fatigue and reduced energy levels.
  • Gastrointestinal upset: Vomiting, diarrhea, and loss of appetite are possible side effects.

2, Doxycycline Treatment Side Effects:

  • Gastrointestinal disturbances: Dogs may experience stomach upset, such as nausea, vomiting, or diarrhea, when taking doxycycline.
  • Photosensitivity: Doxycycline can make dogs more sensitive to sunlight, leading to skin irritation or sunburn with excessive exposure.

3, Steroid Treatment Side Effects:

  • Increased thirst and urination: Steroids can cause dogs to drink more water and urinate more frequently.
  • Increased appetite: Dogs may experience an increased appetite while on steroid treatment.
  • Weight gain: Due to increased appetite and potential changes in metabolism, dogs may gain weight during steroid treatment.
  • Weakened immune system: Long-term or high-dose steroid treatment can suppress the immune system, making dogs more susceptible to infections.

Managing and Minimizing Side Effects

When it comes to managing and minimizing the side effects of heartworm treatment in dogs, there are several strategies pet owners can employ. Here are some guidelines to follow:

  1. Consult with a veterinarian: Before initiating heartworm treatment, consult with a veterinarian who can provide guidance and recommendations based on your dog’s specific condition. They can explain the potential side effects and help you understand what to expect during the treatment process.

Heartworm Treatment in Dogs

  1. Create a comfortable recovery space: Ensure that your dog has a quiet and comfortable area to rest and recover. Provide a cozy bed or crate where they can relax without excessive stimulation. Minimize noise and activity in the environment to promote a stress-free recovery.

  2. Proper nutrition and hydration: During the treatment period, it is important to maintain your dog’s nutritional needs. Offer a balanced diet that supports their overall health and recovery. Provide fresh water at all times to keep them hydrated. If your dog experiences gastrointestinal upset as a side effect, consult your veterinarian for dietary recommendations.

  3. Administer medications as directed: Follow your veterinarian’s instructions regarding dosage, timing, and administration of medications. It is essential to adhere to the prescribed treatment plan to ensure the best possible outcome. Do not adjust the dosage or stop medications without consulting your veterinarian first.

  4. Monitor your dog closely: Keep a close eye on your dog throughout the treatment process. Look for any changes in behavior, appetite, or physical symptoms. If you notice any concerning side effects, contact your veterinarian immediately. Prompt communication and reporting of side effects can help in managing them effectively.

  5. Veterinary support and monitoring: Regular check-ups and follow-up visits with your veterinarian are crucial. They will monitor your dog’s progress, assess the treatment’s effectiveness, and address any side effects that may arise. Do not hesitate to reach out to your veterinarian if you have any questions or concerns.

  6. Follow post-treatment care instructions: After completing heartworm treatment, your dog may require additional care and monitoring. Follow your veterinarian’s recommendations for post-treatment care, which may include restricted exercise, regular check-ups, and heartworm prevention measures to prevent re-infestation.

Every dog is unique, and their response to heartworm treatment may vary. By closely collaborating with your veterinarian and providing attentive care, you can help manage and minimize the potential side effects, ensuring the best possible outcome for your furry friend’s recovery.

Frequently Asked Question

Can heartworm treatment be done at home?

Heartworm treatment should always be administered under the guidance and supervision of a veterinarian. The treatment involves specific medications and protocols that require professional expertise. Attempting to treat heartworms at home can be risky and may result in ineffective treatment or complications. Consult with your veterinarian for the best course of action.

Are there any natural remedies for heartworm treatment?

While there are some natural remedies and alternative therapies promoted for heartworm treatment, their effectiveness is not supported by scientific evidence. Heartworm disease is a serious condition that requires medical intervention. It is crucial to rely on proven treatment options prescribed by a veterinarian.

Can heartworm treatment cause long-term side effects?

The potential side effects of heartworm treatment are usually temporary and resolve with time. However, in rare cases, some dogs may experience long-term effects such as lung damage or persistent respiratory issues. Regular follow-up appointments with your veterinarian are important to monitor your dog’s recovery and address any concerns.

Can heartworm treatment be given to pregnant dogs?

Heartworm treatment can pose risks to pregnant dogs and their developing puppies. It is generally recommended to delay treatment until after the puppies are born. However, the decision should be made in consultation with a veterinarian who can evaluate the risks and benefits based on the individual case.

Can heartworm treatment be administered to senior dogs?

Heartworm treatment can be performed on senior dogs, but it requires careful consideration and evaluation of the dog’s overall health. Older dogs may be more susceptible to side effects, and the treatment protocol may need to be adjusted accordingly. Consult with your veterinarian to determine the best approach for your senior dog.

How long does heartworm treatment take?

The duration of heartworm treatment can vary depending on the severity of the infection and the treatment protocol used. Treatment typically involves a series of injections administered over several months, combined with other medications. It is important to follow the entire treatment plan recommended by your veterinarian for optimal results.

What should I do if my dog experiences severe side effects during treatment?

If your dog experiences severe side effects, such as difficulty breathing, allergic reactions, or extreme lethargy, contact your veterinarian immediately. They can provide guidance on whether emergency care is necessary or if any adjustments to the treatment plan need to be made.

Can my dog be reinfected with heartworms after treatment?

It is possible for dogs to be reinfected with heartworms after treatment if they are not adequately protected. Following treatment, it is crucial to continue with a preventative regimen prescribed by your veterinarian to prevent future infections. Regular heartworm testing and consistent use of preventive medications are essential to keep your dog protected.:


Heartworm treatment is a critical step in saving dogs from the potentially fatal effects of heartworm disease. While the treatment process may come with its share of side effects, it is essential to remember that the benefits of eliminating heartworms far outweigh the potential risks. By understanding the different treatment options available and being aware of common side effects, pet owners can take proactive measures to manage and minimize any adverse reactions.

Early detection and timely treatment are key to a successful outcome in heartworm disease. Regular heartworm testing and preventive measures are crucial for preventing heartworm infection in the first place. However, if your dog does contract heartworms, consulting with a veterinarian and following their guidance is of utmost importance.

Throughout the treatment process, it is essential to create a comfortable and stress-free environment for your dog’s recovery. Adequate nutrition, hydration, and monitoring are essential components of managing side effects. Adhering to the prescribed treatment plan, administering medications as directed, and maintaining close communication with your veterinarian will help ensure the best possible care for your canine companion.



Paula patton is an avid dog lover and pet enthusiast with a wealth of knowledge in pet food and treatment. With her vast experience, she has gained valuable insights into the world of pets and their needs. Through her writings, Paula shares her expertise, helping fellow pet owners make informed decisions for their furry companions. Her passion for animals shines through every word, making her a trusted source for all things related to pets.

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