Cats and permethrins

I can't recall if I've ever talked about this before, but I thought about it when I was doing the 5 things post. #6 would be: if a product is labeled "not for use in fill-in-the-blank species" then DON'T USE IT IN THAT SPECIES.

If you go to Wal-Mart, K-Mart, Target, and the like, you can find over-the-counter flea and tick medications for your pet. These run the gamut from what were once veterinary-only products (Frontline/fipronil, Advantage/imidacloprid, etc) to OTC products that have always been such. If you look closely at certain major brands you will see that several are prominently labeled "DO NOT USE IN CATS."

That is because these products contain pyrethrins/permethrins - chemical compounds that can lead to seizures and death in cats. For some reason however, people tend to ignore these bold warnings and use these products on cats anyway. Some cats will never have any problems, for reasons that are not clear. Other cats will have a mild, tremoring reaction. Still other cats will seizure so hard that they will appear to be levitating.

These drugs kill fleas by screwing up the sodium and potassium channels in cells. These channels are responsible for mediating conduction of impulses along nerves. When these drugs interfere with Na/K, the targeted species (for example: fleas) basically twitch to death because of interruption of normal nerve conduction. The same happens with cats when given these medications. Cat livers are not as efficient at metabolizing certain drugs (such as acetaminophen, the active ingredient in Tylenol and permethrins). As a result, clinical signs develop.

This toxicity can be treated. Unfortunately, most cats (except for the most mildly affected) will require 24-96 hours in the hospital with IV fluids, anti-seizure and muscle relaxant medications, possibly lipid therapy, and intensive care. In some cases, affected cats must be put under general anesthesia with either Propofol or inhalant anesthesia to stop the tremoring/seizuring. In some cases, it cannot be controlled at all.

It is not inexpensive to treat either - which is the saddest part. Most people put these medications on their cats to save money, not realizing that a hospital stay to treat this is going to cost in the neighborhood of $700-2000 depending on the severity (or lead to euthanasia in many cases due to financial constraints). If you break down the math ($60-90 for a 6 month supply of safe, veterinary proved product = $10-15/month) - prevention is the BEST and cheapest treatment.

Lipid therapy is a newer therapy that is very interesting to me. Permethrins are highly lipid soluble. This means that they move into the fat of the body very well. Synthetic lipid compounds are produced by pharmaceutical companies and used often for feeding patients intravenously. It has been found that if you infuse these compounds into patients with exposure to lipid soluble toxins, they form a "lipid sink" for drugs - meaning that instead of being internalized into the body's fat stores, the permethrins are bound up with the lipid we administer. As a result, they are not broken down in the body in such a way as to cause clinical signs. This is the theory anyway.

Lipids themselves are a cheap treatment option (about $20/bag - a small dog will only use about 10-20 millileters, and a bag holds about 500 milliliters). We have this in stock at our clinic, but I haven't had a permethrin case yet! I have used it on a ivermectin toxicity.

Moral of the story: the best treatment? Prevention!