NexGard®, Bravecto®, Simparica®, Credelio® And Their Plus+ Versions That Combat Heartworms And Internal Parasites Too

Unless there is a picture of a cat on the package label, do not give any of these products to your cat

This class of medications has revolutionized flea and tick prevention. They are all very effective, and usually safe for your dog or cat when used as directed on their labels. However, in a few pets, these products have been associated with muscle tremors, ataxia and seizures. 

Ron Hines DVM PhD

 Fleas On Your Pets

  Other Flea & Tick Options

  Products that were verified to cure mange NexGard®  &  Bravecto®

    Hard To Keep Up With All The New Products?

These products are among the newest entrants in our never-ending battle with fleas and ticks. Besides the early released products I put higher in the photo above, Zoetis now mixes their Simparica® ingredient, sarolaner, with moxidectin, so it prevents heartworms and added pyrantel to destroy intestinal worms as well. They call that combination Simparica Trio®. Boehringer-Ingelheim mixes their flea/tick ingredient in NexGard®, afoxolaner, with milbemycin to prevent heartworms and intestinal parasites and markets that as NexgardSpectra®. In addition to Zoetis’ claims for Simparica Trio®, Boehringer states that NexgardSpectra® is an effective treatment for whipworms,   lungworms,   sarcoptic and demodectic mange and ear mites as well. That is because all of these parasites (including ear mites) depend on a bug’s (arthropod’s) nervous system, which is quite different from the one you and I and our furry friends share. (read here)  If your dog has either form of mange, these newer medications are a safer option than the products we veterinarians have had to rely on until now. 

The Isoxazoline Family Of Drugs

All these brands contain similar, related compounds called isoxazolines. Isoxazolines destroy parasites by attacking their nervous system in a similar way that their distant relative, fipronil  (e.g. Frontline®) does. The only difference is that fipronil products are applied to your cat or dog’s hair coat and skin, while the isoxazolines are usually safe to give orally. Fipronil tastes bad and, if licked off the skin, can cause salivation, gagging, or even vomiting.

Although these new products are certainly less messy, easier to administer and longer lasting, there is no data that shows that the isoxazoline family are any more effective than topical fipronil in killing fleas and ticks. Recent studies found no evidence of fleas and ticks having acquired resistance to fipronil or selamectin (Revolution®) Topical products kill fleas and eventually ticks on contact. But isoxazolines require these parasites to suck blood before they become toxic to a flea or a ticks. However, these new isoxazoline products are not subject to being washed off, rubbed off or destroyed by exposure to the atmosphere. They are also more convenient to give and flavored to give them a peasant taste. Patents on the older flea and tick control products produced by these same companies have expired. So, the companies now face much less expensive generic competitors. That is also a major reason these newer products, still protected by the patents they own, are marketed so heavily. 

Who Discovered Them?

In about 2003, several chemists working at a Japanese agricultural chemistry facility (the one in the photo above) were searching for new weed control chemicals (herbicides, weed killers). Through keen observation (serendipity) they noticed that one particular chemical (pyrazinedicarboxamide) killed insect pests as well as weeds. They later discovered that these agricultural pests died because of a loss of muscle function that led to the insect’s paralysis and death. That discover led these chemists to develop a large group of similar compounds. (ask me for Casida2015 if you want to read the whole story) 

Are These Products Safe For My Dog And Cat?

When used as directed on their labels, they are all thought to be quite safe. However, there are no medications for animals or people that do not, occasionally, produce side effects. Veterinarians, physicians and the FDA, the EMA and the MHRA judge medicine safety based on their LD50, and short-term studies (4–9 months). After approval (or tentative approval) they require that the manufacturers revise their product labels or outright withdraw of a product based on feedback (adverse events) from the public and the medical or veterinary profession. 

There is a caution on the label of all of these products that they be used with special care (if at all) in pets with a history of seizures or “neurological abnormalities”.  I mentioned that parasites die because these products affect the parasite’s nervous systems, and that we and our pets have very different nervous systems. But there are some broad underlying similarities which probably account for that label warning. It’s on the older fipronil/Frontline® products as well. I do not believe that any of the isoxazoline products have been tested as to their safety in pregnant or nursing dogs. I would also be cautious about using any of these products in dogs under 4 months of age. I know that studies found that they were safe in puppies as young as 8 weeks old (read here). But those were very limited studies. If you give your kitten or puppy a topical flea control product, and it causes a problem, you can wash it off. If you give your puppy or kitten a product in pill form, there is not much you can do. Bravecto® Topical for cats has on their label that reports exist of that product occasionally causing itching and hair loss in cats. Perhaps that was due to the lag time between application of the Bravecto® and a flea’s first bite. It also takes a while for spot-on formulations to coat the entire body. Many cats have also become highly allergic to flea saliva – something these products have no effect on.

Never apply any of these products in greater amounts than suggested on the product’s insert (instructions) unless your veterinarian agrees that that is a wise thing to do.

There is intense competition between these manufacturers. Each attempts to outdo the others in claims for their particular brand. So, I would take whatever claim they make as to the length of time a single dose is effective in preventing fleas and ticks with a grain of salt. Ticks are always more resistant to insecticides than fleas.

Are They All Alike In Effectiveness, And How Long A Single Dose Lasts?

No.

Bravecto® (fluralaner) differs from the other three isoxazolines with prolonged duration up to 12 weeks, which is three times longer than NexGard®(=afoxolaner), Simparica® (=sarolaner), and Credelio™ (=lotilaner). Some of these products also absorb and metabolize differently depending on if they are taken on a full or an empty stomach. (read here)

Do You Suggest I Use Them On My Dog?

If you got to this page because you are trying to control fleas and ticks on your dog and the products that you are using now are working well for you, I see no reason for you to change. The main advantage of these oral isoxazoline products over topical products is their convenience. You might be advised to switch during your pet’s next checkup because bigbox stores like Walmart now compete with veterinarians by offering lower cost generic flea and tick control products. See here:

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