Flea, Tick Products Linked to Neurologic Adverse Events

September 21, 2018
American Veterinarian Editorial Staff

The FDA is warning veterinarians and pet owners that products in the isoxazoline drug class have reportedly led to neurologic adverse events.

The FDA released an alert this week warning veterinarians and pet owners of the potential for neurologic adverse events in dogs and cats treated with isoxazoline flea and tick preventives. FDA-approved products in this class include Bravecto, Nexgard, Credelio, and Simparica.

Data received by the FDA, as part of its routine postmarketing activities, indicates that some animals receiving these flea and tick products have experienced adverse events such as muscle tremors, ataxia, and seizures.

Even with the reports, the FDA attests that approved isoxazoline products are considered safe and effective for dogs and cats. However, the agency has begun working with manufacturers to include new label information that highlights the potential for neurologic events.


  • The Benefits of Longer-Lasting Flea and Tick Prevention
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Although most companion animals have not experienced neurologic reactions, seizures may occur in animals without a prior history. Because of this slight chance, the FDA explained it is providing its warning so that veterinarians and pet owners can take the reports into consideration when choosing flea and tick products for their patients and pets.

Pet owners whose cats or dogs experience an adverse event while using an isoxazoline product are advised to consult with their veterinarian as soon as possible. Adverse events can be reported directly to product manufacturers:

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

Reports can also be filed directly with the FDA through the agency’s webpage How to Report Animal Drug Side Effects and Product Problems. Veterinarians and pet owners who have additional questions can contact AskCVM@fda.hhs.gov or call 240-402-7002.