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Flea and tick medications causing seizures, other neurological issues for pets, FDA warns

(FOX NEWS) -- The U.S. Food and Drug Administration is warning pet owners that some flea and tick medications can potentially cause “neurological adverse events” in dogs and cats.

The warning applies to drugs in the isoxazoline class, the FDA said. Pet owners who are currently treating their furry friends with Bravecto, Nexgard or Simparica should be wary, as the agency said some animals treated with these medications “have experienced adverse events such as muscle tremors, ataxia, and seizure.”

“Another product in this class, Credelio, recently received FDA approval,” the FDA continued. "These products are approved for the treatment and prevention of flea infestations, and the treatment and control of tick infestations."

While the FDA said it “carefully reviewed studies and other data on Bravecto, Credelio, Nexgard and Simparica prior to approval,” the agency has requested manufacturers of these products to change product labeling to better “provide veterinarians and pet owners with the information they need to make treatment decisions for each pet on an individual basis.”

The FDA says officials closely monitor medications for the first three years after approval. If any reports of adverse effects arise within that time period, the agency then typically releases updated safety information.

Lynn Happel, a Veterinarian with the Eastown Veterinary Clinic in Grand Rapids says that her practice has been using Nexgard and these Isoxazoline’s for several years. If your pet has been taking one regularly without an issue, it is likely safe to continue the use of the product. If you are considering switching your pet to one of these products, watch for any of the side effects listed above with the first dose. If you are using this now and are uncomfortable with the risks, a transition to a topical flea/tick product or the Seresto collar is an option.

Pet owners who want to report adverse effects or would like more information about the warning can contact the various producers:

  • Merck Animal Health (Bravecto): 800-224-5318
  • Elanco Animal Health (Credelio): 888-545-5973
  • Merial (Nexgard): 888-637-4251
  • Zoetis (Simparica): 888-963-8471


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  • Deb hull

    About five years ago my Maltese was poisoned by trifexis manufactured by ElancoI! Although they would never admit fault I did receive a large check for diagnostics!! My Stanley is now on medication to the tune of $40.00 a month to keep him alive and blood test every year at $200.00! I use all natural products to treat my four dogs since this horrific experience!!!!!!

  • Norris Sexton

    I gave our dog i dose of the Simparica and a day latter he could not hardly get up. Three days later he just lays not eating and has mobile problems when trying to walk.
    according to what has been posted about all the side effects this drug should be pulled off the market. I don’t know if my dog is going to survive since there is nothing that can reverse the side effects.
    I think this may be grounds for a law suit and will probably happen if the dog doesn’t survive

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