Not long ago, I wrote about a couple of chewable flea and tick preventatives that are somewhat new on the market that use pesticides as the active ingredients. Preventatives such as afoxolaner and fluralaner are newer forms of pesticides that work in the dog’s bloodstream to prevent flea and tick infestations, and were recently discussed on this site. I wanted to find out what studies had been run on these pesticides, and what anecdotal evidence existed about efficacy, and was surprised to learn about brief limited studies performed prior to the release of these products. I understood this lack of testing should affect how people go about choosing a flea or tick preventative.

Since writing about these preventatives, I have received a few offline messages regarding people who had lost their dogs after administering the product. Here is one of the accounts I received from Deborah Mellor, about her samoyed who passed away not long after a Nexgard treatment. Her family wanted to share her story, which can be found below (edited slightly for clarity).


My 15 year old samoyed was my pride and joy, and we did not give her chemicals at all. She had a bad flea infestation this year, and we did many things. She had a topical treatment at the vet on July 6th, later two doses of Capgard [Editor note: according to product directions/FAQ can be given with preventatives for quick killing of fleas], and then on July 30th was given Nexgard by the vet. I didn’t want to give her the pill but there were still fleas on her, so I was advised by the vets office to give her this Nexgard. Her walking was becoming difficult to begin with, and when I asked them “are you sure it is ok to give it to her”… stupid me I should have not given the Nexgard to her. The next day she could not walk, I believe it messed with her neurological system. 24 hours later she would not even get up, like she was afraid and unable to. She could not and would not get up – she was incapable of standing, as she would just fall.

She was put to sleep today [July 31st 2015]. I do not have proof but I asked the vet if it could be from Nexgard, and the vet said absolutely not. It is too late for my girl but i want to prevent this from happening to others. — Deborah Mellor

UPDATE: There are two very active groups on Facebook about these two drugs. There are regular postings added about dogs who are experiencing similar and severe side effects not long after taking these drugs, suggesting there may be a link between the two. Do remember that this is anecdotal evidence, but it can be useful to help arrive at a decision provided the limited studies and limited time the drug has had on the market.
Bravecto group
Nexgard group

Things to consider before choosing a flea or tick preventative that contains pesticides

The above story is heartbreaking. The samoyed’s family did the best they could regarding her care using the advice of a professional, but they lost her due to a reaction. While we don’t know exactly what happened (accumulation of several products, reaction between products, some other underlying condition that cropped up due to a suppressed immune system caused by the drugs, or something else), it’s a cautionary story particularly because what happened was right after the dog was administered preventatives under the direction of a professional.

And sadly, it’s difficult or impossible to ever pinpoint the exact cause of such a reaction. The studies for many preventatives (including the active ingredient of Nexgard) are short, thus not providing evidence we might need to determine a reaction was caused by the pesticide administered. The study for many of such drugs are run on a small number of young healthy dogs for a short period of time, so it’s safe to assume many variables are not studied (age, breeds, ailments, interactions, and so on). If you don’t know it can cause a problem (because they aren’t thoroughly tested for), perhaps it’s harder to lay blame when it does. Or if the problem is caused because the drug no longer lets the immune system do its job, the blame is placed on that other ailment (cancer, IMHA, etc), and perhaps not on the thing that caused that to happen (the pesticide use). Therefore, anecdotal evidence can be considered alongside many other factors to help you arrive at a final decision regarding care.

We all need to make our own best decisions about our pets for their safety and well-being, especially when dealing with something as serious as a pesticide that enters the blood stream and can affect the immune system. After caring for dogs, these are my personal considerations I make when drawing a conclusion about administering pesticides or similar products. I encourage everyone to research what they can and draw their own conclusions, and provide the following as a guideline for some of the items you may want to consider, think about, or look into further. I encourage you to leave your own considerations, experiences, and thoughts in the comments for this article as well.

My thoughts on the research phase:

  • Anything that is used in or on a dog for a long period of time should be researched with the utmost care as it will have a great impact on overall and longterm health. This can include pesticides, but is also relevant to food, lotions, and other supplements.
  • Never forget about how the product you are about to use affects the immune system. A depressed immune system leaves your dog susceptible to serious ailments, such as cancers and auto-immune disorders. It can also allow pests to flourish, such as heartworms – so a strong immune system can in some cases be used as a pest repellent on its own. Tumors affect more than half of all dogs, and more than half of all senior dogs die due to cancer. This is an incredibly high number, and my feeling is it could very well be in part due to the high exposure to pesticides (both in products such as these, and those used in our environment). If the product you are about to use suppresses the immune system, consider it something to use only when the dog absolutely requires it because he or she does not have any other options.
  • How much can you learn about the product? Or is the product not thoroughly studied (therefore presenting a risk of the unknown)?
  • If the product is new, is the product you are administering similar to anything that has been on the market for a longer period of time?
  • If called “natural”, is it actually true? Many products that are marketed as “natural” aren’t, so make sure you figure out what is synthetic or how much of the product is actually “natural” (often the active ingredient is a synthetic or unhealthy chemical). For example, some synthetic versions of pesticides described as “natural” are quite different in the way they behave. See this article for one example of this.
  • Research and consider the possibility of bio-accumulation, which is when an ingredient (such as a toxin, vitamin, synthetic chemical, etc) can build up in the body over time. Is this a factor for the product? Has it even been researched?
  • Look into possible interactions with other products you are administering: is anything known about how they interact? Has that been studied?
  • Read anecdotal stories: If the product does not have thorough research, is there anecdotal evidence of a problem? Accuracy is always a concern, but a product with a lot of anecdotal evidence of causing illness or death could/should point to a legitimate problem.

Working with vets and a prescription or recommendation:

  • Measure how much your dog is at risk: is there a lot of heartworm in your area? Is there a regular, heavy exposure to ticks?
  • Consider risk to benefit ratios: Does the problem this product solve worth the risk the product presents, or may present (due to lack of study)?
  • Determine if the diagnosis is correct without doubt: is your dog itching because of flea bites? Or could it perhaps be allergies or something else? Make sure you’re solving the actual problem at hand. (Note: I was prescribed a poisonous flea preventative for an itching dog, even when I told my vet “I’ve never seen any fleas, could it be allergies?” My vet said to apply Frontline anyway, and as a new dog owner I complied. I regret that decision wholeheartedly.)
  • Begin with the least invasive options if your dog doesn’t have a need for a quick solution. If those don’t work (and make sure you give it an honest try, search around, be creative), then move on to more risky/invasive measures if and when they’re called for.
  • Consider a holistic approach to info gathering, and make sure you have complete answers. Does your vet encourage or discourage these kinds of questions, or push you towards something without exploring the risks and benefits with you? Is your vet on the same wavelength regarding the type of care you wish to provide your dog, whatever that might be? Try to get a feeling for this, and never feel bad about trying to learn everything you can before reaching a decision. Your dog’s health is your responsibility, you are your dog’s advocate, and you have a right to feel like you have all of your questions answered before making a decision. What you give your dog is 100% your decision to make. Remember it is OK to research online if the sources are reputable, and you use the information to ask informed questions. So make sure, to your best ability, that the answers you receive are complete and unbiased. Trusting your vet and being on the same wavelength there is key. I was definitely not on the same wavelength as the vet who told me to give a flea-free itchy dog Frontline before even exploring allergies, as it sounds like the vet in the above story may have not heeded the concerns of the patient either (nor explored options for removing the few remaining fleas on a very senior dog with a less invasive chemical-free method after administering so many other drugs… such as a bath with Dawn dish soap or dichotomous earth).

I do not believe our dogs should be a science experiment. I hope to never play Russian Roulette with my dogs health, but if I do I hope to make it as safe as possible. It’s true we cannot know or control everything, but I do believe it’s best to go in knowing as much as we possibly can. Because at least then we know we tried to make the best decision we could at the time.

For what it’s worth, I have success using the following multifaceted approach:

  • Raw food or home-cooked diet.
  • Adding garlic and Brewers yeast as supplements.
  • Electromagnetic tags.
  • Essential oil spray as needed (on dog during a hike, or in household such as baseboards and bedding).

This has worked for over 4 years to keep our dogs pest-free, despite having fleas in our house and ticks in the environment when out on hikes.

Note: I am not a veterinarian, and this is not veterinarian advice. Please only use it as a starting point for your own research and conversation with a professional.

Do you have a story to share?

Anecdotal evidence helps other families with dogs make decisions about care. If you have been affected by any drug or product, please feel free to share your story. Send the story in as much detail as possible along with a photo of your dog to jen AT dogthusiast DOT com, and we will help share it to others on this blog. Please make sure to indicate whether you would like your name shared/credited, or to remain anonymous. And of course, the comments are always open for your stories as well.

About Author

Jen deHaan is graphic designer, small business owner, and dog person living in Bay Area, California. Jen enjoys learning about dog training and behavior, and has taken several courses and seminars since 2010. She also contributes articles to leading websites, such as Victoria Stilwell's Positively . It all started with a great dog called Mikey (aka "dude"), loved and lost but remembered forever. Jen also runs a freelance business focusing on graphic, web, and UI design at FoundPixel, and a small business creating hand crafted dog products at Stylish Canine.