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Certain Flea and Tick Meds Can Cause Adverse Reaction in Pets, FDA Warns

Some preventatives have been linked to neurological issues like stumbling, seizures, and twitching in dogs and cats. Here's what you need to know.

by Claudia Kawczynska
June 10, 2021
A dog cuddled up next to its owner on the couch
Duet Postscriptum / Stocksy

Your pet wants you to read our newsletter. (Then give them a treat.)

If you give your dog or cat the flea and tick preventatives Bravecto, Nexgard, Simparica, or Credelio, the FDA wants you to be aware that these medications may cause neurological issues like stumbling, seizures, and twitching in your pet. Though these products are FDA-approved, data received by the agency as part of its post-marketing activities showed the potential for adverse neurological events, and the FDA is calling for manufacturers to include clearer labels that call out these issues.

Bravecto, Nexgard, Simparica, and Credelio are part of the isoxazoline class of drugs; isoxazoline is a pesticide. The FDA noted that most dogs and cats have not had adverse reactions to these drugs and that they continue to be safe and effective for most animals. The agency is urging veterinarians to use their specialized training to review their patients’ medical histories and determine, in consultation with pet parents, whether a product in the isoxazoline class is appropriate for their pet.

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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 monitors adverse drug event reports received from the public or veterinarians, other publicly available information (such a peer-reviewed scientific articles), and mandatory reports from the animal drug sponsor (the company that owns the right to market the drug). Drug sponsors must report serious, unexpected adverse events within 15 days of the event. In addition, they must submit any events that are non-serious, plus any laboratory studies, in vitro studies, and clinical trials that have not been previously submitted to the agency, on a bi-annual basis for the first two years following product approval and annually thereafter.

The FDA is still monitoring adverse drug event reports for these products and is encouraging pet parents and veterinarians to report any adverse drug events. You can do this by reporting to the drugs’ manufacturers, who are required to report this information to the FDA, or by submitting a report directly to the FDA.

To report suspected adverse drug events for these products and/or obtain a copy of the Safety Data Sheet (SDS) 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

Claudia Kawczynska

Claudia Kawczynska was co-founder and editor-in-chief of The Bark for 20 years. She also edited the best-selling anthology Dog Is My Co-Pilot.