A Pill For Fleas & Ticks? Updated!

Fleas and ticks top the list of bugs we hate around our pets and ourselves. We’ll do anything to prevent them, from the old sprays to collars to the newest thing, oral medications. But as you may know, many concerns are being raised with the latest products. My experiences with the Seresto collar have not been good, and sadly many others have had similar problems. And now the FDA is warning veterinarians and owners about the oral products causing neurological and other adverse reactions.

You’ve probably read the FDA notice about these oral flea and tick medications, of the drug class called isoxazolines. Currently, the products implicated are Bravecto, Nexgard, Credelio, and Simparica. Further info on these products and how to report a reaction are found in this FDA factsheet. Before you consider giving another dose of one of these products I urge you to read both of these releases, and consider the number of reports it takes to get a federal agency to release such a statement. Clearly we are not talking about isolated incidences here. In fact, here are the most current numbers from an FDA summary, which you can download at the bottom of the page.

Note that Afoxolaner is Nexgard, Fluralaner is Bravecto, Lotilaner is Credilio, and Sarolaner is Simparica. It should be noted that Credelio (lotilaner) was only FDA approved in January 2018.


These products work on the fleas and ticks by interfering with their nervous system. From the Nexgard insert, “Prolonged afoxolaner-induced hyperexcitation results in uncontrolled activity of the central nervous system and death of insects and acarines [ticks].” Or as Credelio puts it, “… uncontrolled neuromuscular activity leading to death of insects and acarines. ” In layman’s terms, the insect’s brain is hyper-stimulated, causing a seizure-like event, to the point of death. Is it any surprise that the adverse reaction FDA is warning owners and veterinarians about is neurological? After all the neurotransmitter GABA which is affected by the isoxazolines is also part of the neurologic system of mammals, though less sensitive than in insects.

 I’m always cautious about what I put into my dog’s body, especially considering how long it will take to be metabolized and passed out of the body. These oral flea products are effective for at least one month (Nexgard, Credelio, Simparica) and three months (Bravecto).  From the information provided by the manufacturers (links below), it can be determined that the medication is widely distributed in the body, and is slowly removed from the body by the liver through bile. It then passes out of the body in the stool. The products start killing fleas as soon as two hours after administration, and ranged from approximately 93% to 100% effective at their recommended re-dose time (30 days or 12 weeks). So we know that these products are present at insect killing levels for their prescribed time. What we don’t know is how long they actually stay in the body — these studies are either not done or not shared by the manufacturers. For me, this especially concerning for the monthly products, where with each dose given, potential stores of the drug are accumulating in the body. (And of course, there is no way to remove them.)

I confess, I am completely unsurprised by the adverse reactions to these products. First, the obvious reasons. Putting something in the body that is going to be there for a month or longer seems like a ticking time bomb to me, given you have no way to remove it. And with no studies available to say when or even if it leaves the body, we don’t know when or if it will reach a toxic level. We do know that the insect still must bite the dog, so we have not prevented one of our primary reasons for using a flea and tick product. All the monthly products carry precaution warnings for seizures or neurologic signs, and are not evaluated for safety in breeding, pregnant, or lactating dogs. Simparica should not be used in dogs less than 6 months old. Finally, Bravecto carries a warning about not eating, drinking, or smoking while handling the product, and to wash hands thoroughly with soap and water after use. Still want to put one of these products in your dog’s body?

The other reason I’m not surprised by the number of adverse reactions is the small amount of testing required to take these products to approval. I took these values from the drug info found on each products’ website. (Just click on the image to enlarge it.) These were from the ‘well-controlled field studies” done by each manufacturer. The first row shows the total number of dogs in the study group. Only Nexgard shares that some of the dogs lived in the same home. The next row shows the number of dogs actually given the product — the others received a control product which did not contain the drug. So there were 200 control dogs in the Nexgard study, and 70 in the Bravecto study. The third row shows the number of days over which the study was conducted.  Essentially, the time frames took into account what happened up to the time that the third dose of a monthly was effective, or a second dose of Bravecto was effective. Is a two or three dose trial adequate testing? Is testing as few as 182 dogs adequate to call a product safe? I don’t think so!

We’ve seen this before, in both human and veterinary medicine. Remember Vioxx? It was released in 1999 for the control of arthritis pain, and withdrawn in 2004 because of increased heart attack and stroke risk. Remember Promeris, the flea and tick product introduced in 2007 and discontinued in 2011 after an increased risk of the autoimmune disease pemphigus foliaceus was identified? Nexgard was approved in 2013, and Bravecto in 2014, so we appear to be right on schedule for problems to arise. It appears to take about four to five years for a drug to be given to enough of the general population to discover the true incidence of adverse reactions.

So what is the solution? First and most obviously, avoid heavily tick or flea infested areas. This might not always be possible, and may mean you have to find a new hiking spot, at least for some parts of the year. Second, use natural repellents, such as essential oil products. Numerous recipes are available, and I recommend one shared by Dr. Karen Becker. For those who prefer a commercial product, I recommend Wondercide or VetriRepel. Third, if the problem is in your yard, consider ways you can make it less hospitable to insects. Diatomaceous earth can help with sand fleas. Ticks like shaded vegetation, twelve to eighteen inches high. Prevent access to these areas, or treat them with a natural and pet safe product. Consider using thoughtfully placed tick tubes, a way to control ticks on the mice they live part of their life cycle upon. And of course, do a tick check daily, and whenever returning from areas where ticks may be common. If you are in an area that allows it, and have the interest, pea fowl and chickens will feast on ticks and other bugs, as well as providing you with eggs for your and your  dogs’ breakfast!

There may be situations where the problem is so bad that you must use chemicals to get control of these bugs. It’s unfortunate, but it happens. Research your options, and choose what you feel to be the safest. Use the bare minimum needed, and use in conjunction with natural methods when possible. Of course minimize your dog’s access to treated areas for as long as the product recommends, and a couple days longer if possible. Remember, the diseases ticks carry can be serious and in some cases fatal, so do not feel bad for resorting to chemicals in an extreme situation. You may actually be protecting your dog from a more serious risk than chemical exposure.

Ticks and fleas are a serious problem. But these isoxazoline oral products are not the answer. We are just seeing the adverse reactions from the first two released on the market. With the other two released in 2016 and 2018, we can look for more adverse reactions in a few years. How many more products in this drug class are under development? How many will be sold over the counter and as generics, as has happened with topical flea and tick preventatives? The time to stop using these products is now. The FDA has given the warning. Will you heed it?

Below is the complete list of downloadable PDF’s referenced above. The types and number of adverse reactions are broken down by individual products.

Want to see the info sheets from each product? Download a PDF below – you may need to open the file in your downloads folder to see it.

Bravecto

Credelio

NexGard

Simparica

Because of an inordinate amount of spam, comments are closed here. Please leave your thoughts on my Facebook page.

Many thanks to Susan Thixton of Truth About Pet Food, for sharing this info with me. I encourage you to check out her advice on choosing a food for your pet here.

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