Avoid isoxazoline flea and tick meds

Spring is in the air! Did you know that flea and tick medications in the isoxazoline class have been linked to seizures and muscle tremors in dogs and cats? Here’s what you need to know to advise your patients

If you’re wary of recommending flea and tick medications to your clients, you’re in good company. It has been known for a while now that these products can cause serious side effects in some animals. But are you aware of which brands are the most problematic, and why? It’s important to educate yourself about these flea and tick medications — especially those in the isoxazoline class — so you know how to keep your client’s dogs and cats safe.

The products that top the list

On September 20, 2018, the U.S. Food and Drug Administration (FDA) warned animal caregivers and veterinarians about the risk of serious neurologic events, including seizures, muscle tremors and ataxia, in dogs and cats treated with certain flea and tick medications. The warning applies to medications in the isoxazoline class — specifically, NexGard (afoxalaner), Bravecto (fluralaner), Simparica (sarolaner) and Credelio (lotilaner). The FDA updated their release on April 22, 2019 to include another recently-approved product in the isoxazoline class — namely, Revolution Plus (selamectin and sarolaner topical solution).

What you should know about isoxazoline drugs

The isoxazoline class encompasses a group of azolyl phenyl chemical compounds originally developed as parasiticides about 20 years ago. They are now widely used around the world. Adverse reactions to these compounds appear to affect animals randomly, although those with certain chronic diseases, the young and elderly, and animals that are immune-compromised or have the genetic mutation of the MDR1 gene are at higher risk.

When initially designed and synthesized by Dupont Pharmaceuticals, the purpose of the isoxazoline class of pesticides was to inhibit the activation of coagulation factor X activity. Reported side effects include excessive bleeding and hemolysis. More recently, however, a suspected transient neurotoxicity was reported in a seven-month-old female Danish spaniel (Kooikerhondje) puppy. About 24 hours after being administered fluralaner, she exhibited generalized ataxia, muscle twitching or jerks, tremors of the head and body, and oral dysphagia (difficulty or discomfort when swallowing). Thankfully, the puppy fully recovered after ten hours without needing any treatment.

What action has been taken?

Ioxazoline drugs now carry a warning on their labels in both the U.S. and Canada. Also, I am currently part of a privately-convened expert committee that has completed a nationwide survey on this topic — the report should be issued this year. If your client’s pet’s  are not prone to fleas, or they do not live in a tick-infested area, there is no reason to give them flea and tick medications as preventatives. If these pests do attach themselves, recommend to clients non-toxic flea shampoos and combs, or specially-designed tick removal tools, to get rid of them. It involves a little more work, but their dog or cat’s health and well-being is worth it.


Please enter your comment!
Please enter your name here