Are Flea and Tick Preventatives Safe?

By Noël Ziel, Lead Veterinary Technician and Medical Coordinator

This is a common question often asked in veterinary offices. With the advent of the internet and with pet owners becoming more informed about their pets’ care, it is easy to become confused and potentially read misinformation regarding flea and tick prevention. This article will focus on a certain class of drug called the Isoxazoline Class. These brand name products include Bravecto, NexGard, Simparica, Credelio, and Revolution Plus. All of these products treat and prevent flea and tick infestations. We will focus on this class because of their popularity and the recent FDA announcement.

What are Isoxazolines? The Isoxazoline class is a relatively new synthetic chemical class that was introduced in the 2010’s. This drug class has a broad spectrum of insecticidal and acaricidal activity. This means it kills fleas, ticks, and mites. The drug over stimulates the neurological system which causes paralysis and death of the flea, tick, and mite. Mammals have a much lower sensitivity to Isoxazolines, therefore this class of drug is considered safe for dogs and cats.

Because of how the drug works, the Isoxazoline class requires the flea or tick to bite the dog or cat to die. It is not a repellant. This class of drug has been studied and proven to reduce the risk of tick-borne diseases such as Lyme Disease, Ehrlichia, and Anaplasmosis, which have the potential to not only be harmful but also fatal to the pet. Isoxazolines usually kill the tick faster than the tick can transmit the disease, therefore being effective in preventing the transmission of disease. Isoxazolines also have been successful in treating skin mite and ear mite infections.

Depending on the product administered, the drug may be required to be topical (applied to the skin), given with food, or may be given on an empty stomach. The most common side effects of this class of drug include vomiting, diarrhea, decreased appetite, and lethargy. These symptoms are usually self-limiting and resolve on their own. Neurological symptoms such as tremors, ataxia, and seizures have occurred, but are not as common. Because of these side effects, the FDA issued a warning in late 2018 alerting pet owners to the potential for these side effects. But the FDA still classifies the drug as safe and effective for the treatment and prevention of fleas and ticks. If you think your pet has had an adverse reaction to their medication, call your veterinarian immediately.

It is important to discuss all of your pet’s medical history with the veterinarian and to express your concerns. Communication with the veterinarian is the best way to make an informed decision on which products are best suited for your dog or cat to keep them free of fleas and ticks!