We have been able to get in touch with the FDA and some of the manufacturers of the oral flea/tick preventatives that fall into the isoxazoline class – Bravecto, NexGard, Simperica and Credelio.  

Here is some more clarity regarding the Alert and what it means in regards to these products:

Are these products safe?

Yes – in our communication with the FDA, they stressed their statement in the Alert that these products are still considered to be safe.  If they were not considered safe, different actions would have been taken, such as recalling product or removing it from the market.  

If these products are considered safe, why the Alert?

The Alert was deemed necessary, because although they were rare, enough reported events had been recorded across all pharmaceuticals in this new class of drugs – they’ve only been around for 3 years – and neurological side effects are considered significant enough, that a change in labeling of these products was indicated to ensure veterinarians were aware and discussing the potential for adverse effect(s) with pet owners.  

It is also important to understand that in the reporting of suspected adverse event(s) or side effect(s), that investigation into whether or not a product definitively caused the side effect(s) is commonly not performed or possible.  Therefore, it cannot yet be said that reported events were directly because of the pharmaceuticals, but they could have been, and so we take extra precaution and monitor for them.

What is the difference between “Caution” and “Contraindicated” in drug labeling?

“Use with Caution” can indicate that there is potential risk for a side effect in the general population or a potential risk for a side effect in an individual with a certain medical condition.  It essentially means, “watch them closely and report [the side effect] right away if it is seen.”  

For example, if a pharmaceutical has been suspected of causing an allergic reaction in some patients, it may be labeled to “use with caution” in patients with allergies – those with a history of allergies could be considered more likely to have an allergic reaction.  This may not have been proven, but the patient and their doctor should take extra care to monitor for such a reaction – just in case.

”Contraindicated” indicates a high risk for side effect in a specific population: individual(s) with certain medical condition(s), individual(s) taking certain pharmaceuticals or supplements, etc.  

For example, if a pharmaceutical is known to cause birth defects, it would be contraindicated in pregnant females.  

What do we still not know?

Individual case information is not available.  Therefore, we cannot know the individual circumstances or factor(s) that may have influenced each reported event.  We also do not know what their long-term outcomes were.  Often times, the FDA, the pharmaceutical company and/or the veterinarian attending a patient may reach out to pet owners whose pets experienced potential adverse events and be unable to reach the pet owner for follow-up.  

The best way to address this is to communicate and follow up with your veterinarian when a medical situation arises!

What has been our clinical experience?

In Dr. Roush’s clinical experience with canine patients on Bravecto, he has yet to encounter one patient with adverse neurological side effects.  In the past 3 years that it has been on the market, he has seen thousands of patients treated with it with no adverse effects besides an uncommon vomiting or diarrhea side effect and one patient with an allergic reaction to it. 

In Dr. Roush’s clinical experience with canine patients on NexGard, he has yet to encounter one patient with adverse neurological side effects.  As with Bravecto, he has seen thousands of patients treated with it with no adverse effects besides an uncommon vomiting or diarrhea side effect.  Most canine patients that had vomiting or diarrhea side effect(s) had also taken their heartworm preventative on the same day and did not demonstrate the symptom(s) when the preventatives were given on different days.

Dr. Roush has not had clinical experience with Simperica or Credelio – both are relatively new to the market.

Below is further information you can access about each of the products in this class of drugs:


For information about studies published about Bravecto, including safety studies, you can check out the following link: 



More information coming soon


More information coming soon


More information coming soon