Understanding Heartworm Treatment Options
Heartworm disease is a complex, potentially life-threatening condition, and understanding the options for heartworm treatment for dogs can feel overwhelming—especially for pet owners facing financial or logistical challenges. As a veterinarian with years of hands-on experience, my goal in this article is to share practical guidance. Here are some different heartworm treatment approaches for dogs, including the pros and cons of both conventional and alternative options.
Caution: While the insights provided here are meant to help you make informed choices, please note they should not replace professional veterinary guidance. Always consult a local vet wherever possible to ensure any treatment plan is safe and appropriate for your pet’s health needs.
How Can I Find Out if My Dog Has Heartworms?
Heartworms (Dirofilaria immitis) are long, spaghetti-like worms that live in the heart and large blood vessels of your pet. If your dog has the following signs, then heartworms may be the problem:
- Early, or Class 1: If your dog coughs occasionally but seems healthy otherwise, this is the best time to take them in for a heartworm test. Dogs may not even have any problems at this stage.
- Class 2: If your dog tires easily, it is probably not old age and a good time to take them in for a heartworm test. As the heartworms start to change things inside your dog, they cough a little more. But, it is still occasional, and they get tired even after a short walk or a game of fetch.
- Class 3: If your dog has started losing weight and coughing a lot, he might be at this stage. They will be tired most of the time and have signs of heart disease like fluid in the abdomen.
- Late, or Class 4: The heartworms are keeping the blood inside the heart from moving around normally, so there are a lot more signs. They cough all the time, are too tired to play anymore, and are thin because they do not want to eat. Even with surgery, it might be too late to save your dog.
To know if your dog has a heartworm infection, a blood test is necessary, something your local veterinarian must do. They will take a sample, give you the results, and discuss treatment options.
Why Do I Need to Treat My Dog for Heartworm?
If someone with proper knowledge and expertise does not kill the worms, they keep increasing in number and fill up the heart, eventually leading to congestive heart failure. When the worms block the heart and blood vessels, the dog becomes so sick that they can no longer eat or move around. Without treatment, death is inevitable.
What Kind of Treatment Do Experts Recommend?
The American Heartworm Society has decided that the best heartworm treatment for dogs is to kill the adults immediately. To do so, the dog is put on antibiotics and heartworm preventative and is given several injections of an arsenic compound (immiticide) that will kill the worms in the heart. It is expensive, and many people cannot afford it and choose to put their dog to sleep. Others choose to let their pets go on suffering. Numerous shelter dogs die each year because the medication is too expensive. And, treatment is beyond the shelter’s limited resources. Unfortunately, those dogs die too.
What Is the Slow Kill Method?
“Slow kill” is a heartworm treatment for dogs that uses medications that are less expensive than traditional treatment. The newest slow-kill method is used by putting some moxidectin (Advantage Multi) on your dog’s skin and giving him a doxycycline antibiotic tablet to kill the Wolbachia bacteria that help the heartworms thrive. [1] A vet administers the antibiotics for a month, and gives the heartworm preventative every month until the heartworm test returns negative.
In the past, we used a drug called ivermectin for slow kill; then later, an antibiotic (doxycycline) was added to kill the bacteria that heartworms need. Ivermectin does not work as well as moxidectin with doxycycline, and it often takes two years or more to get rid of the adults.
Slow kill is the best choice if:
- you cannot afford the immiticide and need a more affordable option,
- if you live in a place where immiticide is not even available, or
- if you work in a shelter and have a dog that a vet will have to put down because of the cost of the immiticide.
What Are the Pros and Cons of Slow Kill Heartworm Therapy?
Pros:
- Costs less.
- 90% successful after 12 months.
- Not painful. (Immiticide injections hurt a lot.)
Cons:
- Heartworms die slower, so there is more damage to the heart. (Dogs treated with Immiticide and doxycycline usually have a 100% treatment response.)
- Dogs may need to be kept confined longer. (This may not be true, though, and is still being studied.)
- Studies so far do not show a 100% success rate. (The moxidectin is about 50% successful after 6 months and 90% successful after 12 months, though.)
- Sick dogs might die before the treatment is even over. (Dogs already Class IV often die anyway, no matter which treatment is used.)
Is It Better for the Heartworms to Die All at Once or Slowly?
When a worm that lives in the heart dies, it has to go somewhere. And when the body breaks it into pieces, it can break off and lodge in the lungs, causing a disease called pulmonary thromboembolism (PTE). Some dogs can receive treatment for this, but even then some will die. To make this less likely, veterinarians recommend that you keep your dog confined during and after the treatment with immiticide (about 5 months). You will also need to let them know if there are any symptoms.
This disease can happen with the slow-kill method too, but it may be less likely. [4] Dogs are on this medication for a long time so the heartworms might die slower; even when let out in the yard like normal, they have fewer reported side effects. No one is sure why at this time, but it may be because the worms die more slowly, and the body has more time to break them down so that they do not break off into large pieces and clog the lungs.
Will My Dog Get Better Faster if I Give Him Heartgard and Advantage Multi?
Heartgard contains ivermectin, a drug to kill the small heartworms (microfilaria) before they develop into adults. Advantage Multi is a product on the market with moxidectin that kills the small heartworms too. Research has shown that a combination of the two is more likely to kill the adults. [2]
If you decide to give your dog both so that they might get better sooner, they still need the antibiotics every day for the first month, then give ivermectin (Heartgard) and moxidectin (Advantage Multi) every month. Giving several medications is more expensive than giving just two, but the heartworms die faster, the dogs will have less heart damage, and they will be healthier sooner.
Can I Find a Veterinarian Willing to Treat My Dog?
Finding a veterinarian willing to treat your dog with the slow-kill method may not be easy. The American Heartworm Society recommends that the dogs receive treatment with immiticide. Finding a veterinarian willing to use moxidectin in their clinic as a heartworm treatment for dogs can be a challenge. Veterinarians cannot sell medications without a patient-veterinarian relationship. So, even if the vet wanted to send the medications home, they could not do so.
If you cannot afford heartworm treatment but your dog tests positive at the veterinarian, explain that to them and tell them that the animal will die because you cannot afford treatment. Many veterinarians will discuss the alternative solutions with you and search for a way to help your dog. If they are not willing to help and you are not willing to pay for the arsenic injections, you can look at the home alternative.
Can I Treat My Dog for Heartworm at Home?
Both medications used in the slow-kill method are only available by prescription in the US. If you want to treat your dog with this method and cannot afford a veterinarian or find one willing to help, you can purchase the doxycycline for fish and give it at 10 mg/kg once a day for a full 30 days. The medication will cost around $50 for one month.
You will need to get an accurate weight on your dog and this medicine can cause vomiting so you might need to decrease the dosage to half if they get sick. (It does not work as well in getting rid of the bacteria that helps heartworms survive.)
If you do decide to purchase your heartworm medication in Canada or Australia, where you will not need a prescription, be sure to read the label and buy only a product similar to Advantage Multi that has topical moxidectin. (There are some other products with moxidectin but only that one has the topical solution that has been studied.) It will cost about $10 a month to treat a small dog, and they will need to receive the medication every month.
The use of moxidectin is not without some problems. An injectable solution used to be available but was pulled from the market because of the frequent side effects. The topical, which is what you should use, is safer and has few side effects. Your dog might experience irritated skin at the application site, be itchy, and have a poor appetite.
Always keep dogs under this treatment in the house or a kennel in the backyard so that they do not run too often. You should not take your dog for a long hike or play ball or frisbee with them while they are receiving treatment for heartworms.
You will need to go back to your veterinarian and have your dog tested for heartworms after a year. If he is still positive, then you should put them on another month of the antibiotic doxycycline, and if the test is negative, they can receive heartworm preventative every month or as needed in your area.
Are There Herbal or Natural Heartworm Treatments That I Can Use at Home?
You may wonder if there are any natural heartworm treatment options for dogs. Several herbal cures are sold but none have been tested or shown to work.
- Black Walnut Hull: Numerous people suggest giving one drop on the food once daily for every ten pounds of body weight. Another suggested giving only one drop the first week, another drop the next week, etc. Some have also suggested it as a heartworm preventative (at a capsule a day of the ground herb) but there is no data about that either, although there are anecdotal reports of diarrhea. (5)
- Wormwood: Most brands on sale are between 300 and 500 mg. The number of drops or the number of capsules is imprecise; one capsule twice daily seems to be a common suggestion.
- Cloves: One capsule once daily. The strength varies considerably, depending on the brand.
- Mugwort: Two to three artemisia capsules twice daily. (Some capsules are sold with a 500 mg label; some do not list the amount of herb contained within.)
- Garlic: One clove per ten pounds once daily. If the active component of garlic is to be given, the herb should be fresh, not encapsulated.
- Coenzyme Q10: This is not an herb but an enzyme present in the body at all times; it markets to improve the function of the heart. Its dosage is around 100 mg per day, but you can open the capsules and divide them for smaller dogs. (Some holistic vets recommend this for heartworm prevention too but there is no proof of its efficacy.)
Worms in the heart are a serious problem that will cause a dog to die a slow and painful death. I would not trust any of these products to do the job and kill the heartworms already living in my dog.
What Heartworm Treatment Is Going to Be Best for My Dogs?
There is enough research available now that shows that the slow-kill method works. (6) The immiticide treatment method, where all of the adult worms are killed quickly and the dog is allowed to rest while the worms are being broken down, is still the best way to treat a dog. It will cause the least damage to the heart and is typically a vet’s first recommendation.
Final Thought
When considering heartworm treatment for your dogs, if you cannot afford the immiticide treatment, it is much better to use the slow kill method, in my opinion. Unfortunately, we cannot ask our dogs, but I think most of them would prefer a 90% chance of recovery to immediate death. If you have any questions about this article, please leave a comment below or submit a question to me in our Ask a Vet section.
References
(1) Genchi M, Vismarra A, Lucchetti C, Viglietti A, Crosara S, Gnudi G, Quintavalla C, Schaper R, Kramer L. Efficacy of imidacloprid 10%/moxidectin 2.5% spot on (Advocate®, Advantage Multi®) and doxycycline for the treatment of natural Dirofilaria immitis infections in dogs. Vet Parasitol. 2019 Sep;273:11-16. https://pubmed.ncbi.nlm.nih.gov/31442887/
(2) Bazzocchi C, Mortarino M, Grandi G, Kramer LH, Genchi C, Bandi C, Genchi M, Sacchi L, McCall JW. Combined ivermectin and doxycycline treatment has microfilaricidal and adulticidal activity against Dirofilaria immitis in experimentally infected dogs. Int J Parasitol. 2008 Oct;38(12):1401-10. https://pubmed.ncbi.nlm.nih.gov/18433753/
(3) Savadelis MD, Day KM, Bradner JL, Wolstenholme AJ, Dzimianski MT, Moorhead AR. Efficacy and side effects of doxycycline versus minocycline in the three-dose melarsomine canine adulticidal heartworm treatment protocol. Parasit Vectors. 2018 Dec 27;11(1):671. https://pubmed.ncbi.nlm.nih.gov/30587225/
(4) Ames MK, VanVranken P, Evans C, Atkins CE. Non-Arsenical heartworm adulticidal therapy using topical moxidectin-imidacloprid and doxycycline: A prospective case series. Vet Parasitol. 2020 Jun;282:109099. https://pubmed.ncbi.nlm.nih.gov/32450463/
(5) Wynn SG, Fougère BJ. Veterinary Herbal Medicine: A Systems-Based Approach. Veterinary Herbal Medicine. 2007:291–409. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7151902/
(6) Jacobson LS, DiGangi BA. An Accessible Alternative to Melarsomine: “Moxi-Doxy” for Treatment of Adult Heartworm Infection in Dogs. Front Vet Sci. 2021 Jul 27;8:702018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8353148/
