FDA Fact Sheet on Isoxazoline-containing Flea and Tick Products, Including Credelio

Dr. Mark Kummer, Medical Director


The FDA released a Fact Sheet today to help ensure that pet-owners and veterinarians are aware of potential neurologic side effects from flea and tick preventive products containing that contain the Isoxazoline class of medications.  These products include Credelio (the flea/tick preventive recommended by Fairhaven Vet for dogs), Nexgard, Bravecto and Simparica.

It is unclear as to why the FDA released this fact sheet.  The potential for virtually all effective flea/tick products to very rarely cause neurologic signs is well-known, but they are considered safe for the vast majority of animals.  Dr. Kummer has emailed the FDA to enquire as to whether there is specific reason that Isoxazoline products have been highlighted by the FDA – We know of no increased risk of Isoxazoline flea/tick products relative to other effective products, but if a problem is becoming apparent over time, we certainly want to know and will keep you alerted!

Modern flea/tick products, including the Isoxazoline medications, target the insect neurologic system preferentially over the mammalian system.  They have proven to be very effective, and usually very safe.   We have been recommending Credelio as our preferred flea/tick product for dogs for nearly a year, and used Simparica prior to that.  We have had very few reports of any side effects.  The first Isoxazoline flea/tick product, Nexgard, was approved 5 years ago in 2013 and has had very widespread use ever since, being used in many millions of dogs.  Unfortunately, “natural” products (garlic, brewer’s yeast, cedar-oil, citrus-oils) are simply not effective and can be toxic as well.  Treatment of the home with Diatomaceous Earth (FleaBusters) to desiccate the environment and shrivel-up flea eggs can be effective over time, but can also lead to asthma and other respiratory problems.

All medications have potential side effects that must be weighed against the benefit that they offer.  We continue to believe that effective flea and tick control is very important to the health of our patients.    Our flea-season has steadily broadened and is now nearly year-round.  Fleas cause severe skin inflammation and secondary skin infections in many dogs and cats, can spread blood parasites (Hemoplasma) in cats, and can cause severe anemia in small animals.  We have also seen a significant increase in ticks in our area over the past 2-years.   While tick-borne illness are still uncommon locally, they are have risen sharply nationally, and we are concerned that they may become more prevalent here.

We continue to believe that Credelio is a very safe and effective flea/tick preventive product for the vast majority of our patients.   But, you must make this decision for your pet.  If you have concerns, please let us know.  We are here to help!   Animals who are suspected to have had an adverse reaction should certainly be switched to different class of flea/tick protection.  In animal’s with known seizure disorders, it is generally safest to use only topical products that do not get absorbed systemically, but they are significantly less effective.  (We recommend Frontline TopSpot, but its efficacy has waned significantly;  Many experts recommend application every 2-weeks to improve its effect.)

If you believe that your animal has experienced an adverse reaction to Credelio or any flea/tick product, PLEASE LET US KNOW so that we can help ensure your pet receives appropriate care, report the incident to the FDA, and help direct future flea/tick control.