Isoxazoline Flea Treatment and Seizures


This article is written by Pet Circle veterinarian, Dr Josepha Cox BBiomedSc(Hons) DVM

Isoxazoline's are a class of broad spectrum antiparasitic drugs frequently used in dogs and cats to protect against parasites such as fleas, ticks and their associated diseases. In Australia the common products in this class include Bravecto/Bravecto Plus, Nexgard/Nexgard Spectra, Simparica/Simparica Trio, Credelio/Credelio Plus, and Revolution Plus.

Their effectiveness is second to none and since their introduction to the market around 8 years ago, they have significantly impacted the veterinary industry and pet health in a positive way. According to many veterinarians working in tick prone areas the number of dogs and cats suffering from tick paralysis has dropped dramatically since the widespread use of Isoxazoline's. This is welcome news as many of these cases are not only very costly to treat but can be fatal. The use of these products today has become even more essential because as of November 2022, Australia is experiencing a nationwide shortage of tick antiserum - the vital component for treating tick paralysis. This means protection against ticks and prevention of this disease is more important than ever.

Most vet clinics around the country will happily stock and dispense Isoxazoline products and many vets will gladly use them on their own pets. However, there has been some hesitancy for their use among the general public as there have been neurological issues such as seizures, tremors and incoordination linked with their use.

While there have been numerous reports of this side effect it is often very hard to determine whether the Isoxazoline is the sole cause of the issue or whether they would have developed the symptoms regardless. Despite this, a number of regulatory agencies and the manufacturers of these products have included warnings of these rare but potential adverse events.

The good news is most dogs and cats that use these products do not develop neurological problems. Many thousands of these products are used safely every year. However, those with a prior history of seizures may be more at risk and some pets can experience these issues even without a previous history.

What does this mean for my pet?

For most pets Isoxazolines are safe to use but as a starting point it's always important to discuss any concerns with your veterinarian. Your pets medical history as well as the risk of ticks in your area can be taken into consideration as to whether these products would be suitable for them.

As a general recommendation:

Those in paralysis tick areas (the east coast of Australia) should use these products. Most Australian veterinarians would agree that the benefits of preventing potentially fatal tick paralysis is worth the low risk of adverse effects.

For pets with a history of seizure conditions living in these areas they should consult with their veterinarian as there may potentially be a greater risk of developing side effects. There are other products such as Advantix (dogs only) or Seresto (dogs and cats) available for tick protection that do not have the same potential adverse events as Isoxazolines; however, they are typically less effective. Having said that, using these products would be much better than no tick protection at all.

Those living in non-tick paralysis areas can happily choose to use either an Isoxazoline or the other products mentioned above. Having tick protection despite the low risk of tick paralysis is still beneficial as this will protect against other species of ticks such as the brown dog tick and the bush tick which can still cause irritation and disease. In some areas of Australia such as in the Northern Territory and Western Australia, Advantix and Seresto are the preferred options given the higher risk of Ehrlichiosis. You can read more about Ehrlichosis here or ask your vet for further information.