Flea and Tick Medicines Increase Seizure Risk in Pets, FDA

If you are a dog or cat owner, the FDA warns that certain flea and tick medicines may increase seizure risk in your pet.

The class of drugs known as isoxazoline showed increased risk of neurologic events in dogs and cats, even absent a prior history of seizure. The FDA approved this class of drugs after finding them to be both safe and effective to treat and prevent flea and tick infestations.

The FDA has no plans to remove the drugs from store shelves, but they also want all dog and cat owners to know of the increased risk of negative neurologic reactions including muscle tremors, ataxia (loss of muscle coordination, especially in the extremities), and seizures. The FDA will require manufacturers to add new package warnings about these increased risks.

The brand names on this class of drugs include Bravecto, Credelio, Nexgard, and Simparica. These flea and tick medicines are usually sold as flavored chewables.

If you are concerned about the risk to your pet, consult with your veterinarian to see what else is appropriate for use. There are other flea and tick medicines available that do not contain this class of drug.

Of course, immediately consult your vet if your pet suffers any adverse reactions to their flea and tick medicines.

You should also report adverse reactions and side effects to the respective manufacturers, and to the FDA directly at www.fda.gov/animal-veterinary/report-problem/how-report-animal-drug-and-device-side-effects-and-product-problems.

Contact manufacturers directly at:

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

You can also ask additional questions at AskCVM@fda.hhs.gov or call 240-402-7002.