When new products appear on the market, we need to do a little homework first, before using them. Such is the case with one called Cheristin. First released, I believe, as Assurity, or Comfortis, this drug has been shown to be too toxic for some animals, especially certain cats. It was repackaged and then recently re-released as Cheristin For Cats.
My friend "Sue" lost her very best friend in June to a preventable, though uncommon, condition in which the active ingredient seeped into her cat's brain and slowly caused her to suffer a horrific death due to the symptoms that accompany neurotoxic paralysis. She was only 9 years old and in peak health, weighing in at 13 pounds. When she died, she was only 7 pounds. She had numerous symptoms indicating neurological damage, including a "circling" behavior and loss of balance. Only one of the vets consulted took note of the symptoms, but it was too late.
There is a test for dogs to see if the genetic defect exists. Since the test examines the individual's DNA, it seems reasonable to expect it could be useful in cats, too. But no one has done, or is doing, research in this area. Here are the only two labs testing dogs at this time:
As for dogs, the defect seems to be most common in the herding breeds and protocols exist to deal with it, such as lists of drugs to avoid and the breeds most affected. Interestingly, and possibly critical, is the presence of white on the legs or feet. The anecdotal evidence with cats has so far included the presence of white paws. Is it possible the defect exists on the gene(s) that dictate foot or leg color?
Because the defect is about the animal and not the drug, the companies that produce it, such as Elanco, simply refuse to recognize this problem. There are no warnings on the product, and certainly no sympathy if your pet succumbs to the use of it. The attitude is, "Not our problem." It's not common, and their claims of safety are valid as long as the genetic defect does not exist.
Pet owners have few resources to address this, however, there is one major method of preventing it from killing your pet: Don't use drugs that have not been approved by the FDA (such as this one, which is only approved by the EPA). Or, even better, use only natural products with a good track record. If possible, have your animal tested before embarking on a new protocol. Also, do some research. Be aware that most veterinarians will be unaware of this problem since it is relatively new, no research exists for cats (yet), and little has been published by other than anguished pet owners.
In any case, spread the word. Report incidents to local vets and ask them to share with other vets. Call news outlets to do a story. If they are not interested, try writing a letter to the editor. Collect documentation on your pet's case. Take photos. Save any test results you obtain from your vet or any labs that have tested your pet. Report to your state veterinary board. The more these agencies hear about victims, the sooner they may take notice and start doing something.
For more information, here is a Facebook page that focuses on the same or similar formula for dogs, called Trifexis:
See also: http://thecatsite.com/t/323184/do-not-use-cheristin-for-cats
If you find other sites with more information, please feel free to share them in the comments. We are all still learning about this and need updated info and more stories. Thank you.