I was asked on Facebook to comment on the report of an adverse incident following the use of the oral anti-flea and tick medication Simparica. Here's what I had to say:
Simparica is indeed a common flea drug. It's one of a family of four chemically-related oral flea medications, Nextra, Bravecto, Simparica, and Credelio. All are members of the isoxazoline family, which work by targeting the fleas' and ticks' nervous system receptors.
A veterinarian, Elizabeth Carney, DVM, has been following and documenting the first three of these drugs for years on her blog, Your Pets Need This. You can find her excellent posts, which include FDA Adverse Drug Event Reports (ADEs) which she had to obtain by filing Freedom of Information Act requests (FOIAs), by searching for them on her site. You'll see the three most recent on her home page, but there are many more. On the basis of her findings, Dr. Carney has decided not to prescribe these drugs or to use them on her own pets.
Here is the safety warning from the Simparica website:
"IMPORTANT SAFETY INFORMATION: Simparica is for use only in dogs, 6 months of age and older. Simparica may cause abnormal neurologic signs such as tremors, unsteadiness, and/or seizures. Simparica has not been evaluated in dogs that are pregnant, breeding or lactating. Simparica has been safely used in dogs treated with commonly prescribed vaccines, parasiticides and other medications. The most frequently reported adverse reactions were vomiting and diarrhea. See full Prescribing Information."
Your mileage may vary.
As for me, I fully agree with Dr. Carney. If I were still in practice, I, too, would not prescribe them. The adverse neurological events, while uncommon, are quite dangerous. There is no antidote, and no way of removing the drug from the body.
As a general principle, I am not keen on any flea or tick treatment, oral or injectable, which works by getting the drug into your pet's bloodstream. In order for the drug to work, the flea or tick must first bite your dog. None of these drugs have any repellent effect whatsoever. That means that whatever harm can occur from the bite will occur. For example, fleabite allergic dermatitis, or flea allergy, is caused by a component of flea saliva which reacts with one of the body's immune system chemicals, complement, to form the substance that triggers the allergy in susceptible pets. Killing the flea after it has already bitten will obviously do nothing to improve the situation. It's possible to make a slightly better case for the drug's usefulness as a preventer of tick diseases, since the most serious require the tick to remain embedded for a number of hours in order for transmission to occur. However, the irritation, itching, and skin infection from whatever organisms are present in the tick's saliva will still occur.
Think of it – how would you like to fight mosquitos by swallowing a pill, turning your own body into poisoned bait, then standing there and letting the mosquitoes feast on your generous all-you-can-eat buffet because you know they'll die afterwards? Wouldn't that be a Pyrrhic victory?
