FDA warns pet owners, vets of adverse effects in some flea, tick medicines

SILVER SPRING, Md. — The U.S. Food and Drug Administration warns pet owners and veterinarians that some flea and tick medicines may have adverse effects in dogs and cats.

The FDA announced Thursday that some products in the isoxazoline class have caused some animals to experience muscle tremors, ataxia, and seizures.

The medicines reportedly include Bravecto, Nexgard, Simparica and Credello, which are all FDA approved for treating and preventing fleas and the control of tick infestations.

The FDA says it is currently working with manufacturers of isoxazoline products to include new labels that highlight these neurological events that have been consistently seen throughout the class of product.

The FDA said, “Although FDA scientists carefully evaluate an animal drug prior to approval, there is the potential for new information to emerge after marketing, when the product is used in a much larger population. In the first three years after approval, the FDA pays particularly close attention to adverse event reports, looking for any safety information that may emerge.”

The FDA encourages pet owners and veterinarians to monitor adverse drug events and says that if your dog or cat experiences an adverse reaction, you should contact your veterinarian.

To report suspected adverse drug events for these products and/or obtain a copy of the Safety Data Sheet or for technical assistance, contact the appropriate manufacturers at the following phone numbers:

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