Heartworm Prevention for Dogs with Food Allergies

Did you know that there are unflavored monthly heartworm preventative chews?


Did you know that there are unflavored heartworm preventative chews available, as well as other forms of preventatives? I didn’t either, until recently. 

Pixel, my sister’s dog, was just diagnosed with a gastrointestinal disease that was causing inflammation of her intestinal tract and malabsorption of food. Fortunately, this condition was quickly resolved by changing Pixel’s diet to a novel protein and eliminating any foods with beef, pork, or chicken and she is now thriving. Then it became time to administer her monthly chewable heartworm preventative. My sister hesitated: The chewable preventative medication that she ordinarily used to protect Pixel was flavored with chicken, which Pixel couldn’t have. Fortunately, there are alternatives, and Pixel’s veterinarian was happy to change Pixel’s prescription to one of these.

Heartworm disease is a serious and potentially fatal condition caused by Dirofilaria immitis, a parasitic roundworm that is transmitted to dogs through the bite of a mosquito. Unfortunately, canines are natural hosts for the parasite, and once it infects a dog’s body, the larvae mature into adults, mate and reproduce, with the adult forms of the heartworm residing in the heart, lungs, and associated blood vessels. Heartworm disease can cause lasting damage to a dog’s body and have a long term effect on health and quality of life. Heartworm disease has been diagnosed in all 50 states; risk levels for contracting the disease vary and are difficult to assess. Accordingly, prevention is usually necessary in most areas. Heartworm medications do not actually prevent the transmission of the heartworm, but rather they act to destroy the larval stages of the parasite, preventing the development of the larvae into adult heartworms. 

Prevention of heartworm disease is usually achieved by the monthly oral administration of a flavored chew, which is highly effective when administered correctly. Most oral heartworm preventives, however, contain a protein-based component for flavoring, usually pork, soy, beef, or chicken, in their formulation. Because many dogs suffer from food allergies and sensitivities or are undergoing food elimination trials (and flavorings can interfere with and affect the success of the trial), heartworm prevention in these cases should be changed to a non-flavored oral formula or topically applied product. 

The monthly heartworm preventive HEARTGARD® (ivermectin) is available in an unflavored tablet form and does not include any food ingredients that may trigger an allergic reaction. A topical (applied externally to the body) heartworm preventative, such as Advantage Multi, Revolution, or Selarid, is another option, especially as this form completely bypasses the gastrointestinal tract. 

There is a third option: ProHeart 6 and ProHeart 12 take the form of sustained released injections of moxidectin (this ingredient is also available as a topical) and provide protection from heartworm infection for six months and twelve months respectively. Its use in the U.S., however, still draws controversy over concerns regarding adverse effects (ProHeart 6 was taken off the market in 2004 because of safety concerns, but it was reformulated and returned in 2008; ProHeart 12 was approved for the first time by the FDA for use in the U.S. in July 2019). In other countries, both products remain on the market and are in use.

As always, consult with your veterinarian about your dog’s prescription heartworm preventative.

Featured photo: Jasmina007/Getty Images

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Barbara Dobbins has been writing for WDJ since 2011 with a focus on veterinary and canine health topics. Her lifelong fascination with dogs has led her in many directions. As a youngster she would round up her dogs and horse for a day of adventure exploring and searching for buried treasure in the California hills. Inspired by Margaret Mead with a nod to Indiana Jones, she went on to study anthropology, archaeology, and museum studies and obtained a masters degree in art history. Then two new puppies bounced into her life, and Barbara launched into studying animal behavior and training and spent hundreds of hours volunteering in the behavior department at her local shelter. When her beloved Border Collie Daisy was diagnosed with a rare cancer, she dug deep to research all she could about the disease, and has written extensively about all sorts of canine cancer for Whole Dog Journal. Liaising between pet owners and veterinary practice, science, and research, she synthesizes these complex and data-driven subjects into accessible information. She continues to take inspiration from her two research assistants, mixed-breed Tico and Border Collie Parker.


  1. i give my 11 dogs Ivermectin, the injectable stuff by mouth. With the approval of my vet. it has a wide safety margin and it usually well tolerated. Added to their food they take easily. It is available without prescription at my feedstore or online.

  2. Does it make sense to give your dog a little bit of poison every month to keep them healthy? My holistic vet recommended that I not give monthly ivermectin, and instead do heartworm test 3 or 4 times per year. As the article states, it is not a heartworm preventative, but kills the babies, when they are still small enough to be cleared from the blood vessels easily. So if my dog does test positive , the less-than6 month old babies will be cleared by giving a dose of ivermectin. I think that’s a better use of a pesticide in my dog than giving it monthly.

  3. I’m having a very hard time finding unflavored ivermectin — anywhere (on the web). I found one site but a 6-pack expires the end of November (2020). I know there have been shortages before, but I thought those had been resolved. My vet doesn’t carry the product. And the practice in Wisconsin I found that does have it — only dispenses to existing patients (I’m in New York). Please help.

    • look for injectable ivermectin for cattle at feed stores. generally you can give just one single drop orally. i wouldnt try it if your dog is tiny though, would be too much of an overdose. but i did that with my 50 pound dogs for 10 years or so.

  4. Hi Deborah, I read your input about it being difficult to find an “ivermectin” Heart Worm “unflavored”!
    I, too, am finding it difficult to find!
    Have you FOUND an “unflavored” product, yet?
    PLEASE reply if you have OR have not found a solution, PLEASE!
    Maybe we (together) can find a solution!