Pyrethrins and its cousins: a veterinary perspective on the good, the bad and the ugly
I was inspired to write this article after seeing another article on pyrethrum written by adinamiti recently. And then that very night seeing a poisoning from this toxin during my overnight shift at the local veterinary hospital. As you might guess, with all toxins, there are some good things and some bad things about them. I will try to cover both in this article.
Pyrethrins are one of the oldest insecticides used by man. These toxins are natural products of the Chyrsanthemum cinerariaefolium or the Dalmation Daisy, which is not a succulent or palm, so I do not know much about it other that what I can glean on line. This plant looks a lot more like a Daisy than any Chrysanthemum I have seen, and some taxonomists have put it in another genus, Tanacetum.
Pyrethrum aka Tanacetum cinerariaefolium (Photo Wikipeidia)
The poison is a neurotoxin with fairly low toxic effects on people, relative to its effect on insects. At low doses it works as a repellent for insects, but at higher doses it kills them by over-exciting their nerves. At very high doses, it can be a fairly toxic product for all forms of animal life. However, many consider it one of the safest insecticides there are due to its relative low toxicity for most animals and for its rapid degradation in the environment down to harmless compounds. It has been used as a louse powder for over 100 years. Currently it is used on crops and all sorts of food stuffs as well as extensively in the pet industry as a repellent and killer of fleas and ticks. Around the home it is used for all sorts of ‘bug problems’, including ants, lice, spiders, wasps, earwigs, crickets, silverfish, bed-bugs, flies, mosquitoes, roaches, scorpions etc. One will often see it referred to as the safest environmental insecticide (though, sadly, not too safe for fish until it degrades).
two products sold at stores and advertised as 'natural' bug killers, containing pyrethrins- notice they kill all sorts of arthropods (non-selective killer)
Two pyrethroid products used to kill 'bugs' indoors (pyrethrin is Bifenthrin)
One of the downsides with this product is some animal’s unique sensitivity to it. Unfortunately, two of our pet creatures, the fish, and to some extent, the cat are very sensitive to all the natural forms of this product, though the latter has shown much more sensitivity to most of the synthetic forms of this poison. But as mentioned, all animals are sensitive to this poison if the concentrations are high enough.
The symptoms in mammals of pyrethrin toxicosis are hypersalivation, weakness, vomiting, muscle tremors (one of the more recognizable symptoms), seizures and death. In humans, other symptoms include asthma-like respiratory problems, sneezing, headache, nausea, incoordination, tremors, convulsions, redness of the face, and swelling, burning and itching of the skin. Longer term exposure has lead to possible brain defects in babies from exposed mothers (probably due to the synergist often accompanying pyrethroid toxins in most products). And there is some evidence for carcinogen effects in rats as well.
The synthetic forms of pyrethrins, called pyrethroids (including the most common one, Permethrin) have the potential for a lot more toxicity than ‘natural pyrethrin’. Additionally, a synthetic synergist is often used along with pyrethrins and pyrethroids (usually Piperonly Butoxide- a synthetic sassafras oil) for the primary reason that many insects over the years have developed excellent resistance to the pyrethrins. This synergist stops the insects natural enzyme breakdown of the pyrethrins and pyrethroids into less toxic compounds. The end result is an even more lethal toxin.
Pet Relevance and a personal point of view.
Pyrethrins, for the most part, do seem to be relatively safe for most pets, though dosage is still the key. Many on-line sites list pyrethrins as being safe for cats, and as far as we can tell, used judiciously, they are not too much more toxic for cats than they are for dogs. But unsafe levels are not that difficult to attain, particularly in felines, so for some reason if you feel the need to use these products in cats, please read instructions carefully.
Pyrethrin product for both cats and dogs (note photo of both on the label)
Pyrethrins are used as topical toxins in pets, but some degree of skin absorption takes place. This amount is presumed to be insignificant. But some dogs and most cats tend to lick off topical products. Fortunately natural pyrethrins break down quickly in the gastrointestinal tract so dogs and cats that lick off their pyrethrin soaps or powders rarely suffer from more than some heavy salivation and mild vomiting.
Pyrethrin spray supposedly safe for kittens- these pets will lick this off so it HAS to be pretty mild (but effective??) -left; right is shot of a pyrethrin shampoo for dogs only... is this a too concentrated for cats? No explanation is provided
The Bad: Pyrethrins have been used for flea and tick control in pets for many many decades. For those of you readers who are too young to remember a time before Imidacloprid, Fipronil, Selemectin, Spinosad and a few more newer products, there was a time (over 20 years ago) when flea control was a nightmare in pets, due primarily to the flea’s ability to develop resistance and/or detoxify this poison. Even at higher doses considered still safe for pets, many paralyzed fleas eventually recovered in time. Resistance was not futile! So flea control was a constant and ever-losing battle. The resurgence today of Pyrethrin products has been largely due, in my opinion, to the discovery and use of much safer and more effective products in the last 20 years, and the public’s inability to distinguish these excellent, safe and effective products from the ones that have not been effective for more than 30 years.
Pyrethrin shampoo for dogs and cats. These products are not very effective at killing fleas (years of personal experience) and most flea shampoos are somewhat drying and irrititating to the skin- many dogs and some cats are itchier after the shampoo than before it. For good flea contol and less itching, I recommend bathing a pet with a soothing oatmeal shampool, apply a conditioner afterwards to help remoisturize the skin, wait 24 hours and apply a much more effective topical product, or oral Spinosad... THAT will control fleas well!
Though I have not seen too many toxic reactions in cats, a few cats bathed repeatedly in pyrethrin shampoos or accidentally treated with canine dose pyrethrin products, have had some mild to moderate toxic reactions (drooling, tremors and vomiting). I have not seen one die of this toxicity, though. Some of these cats still need to be hospitalized, rebathed and treated for their tremors and rehydrated. Though pyrethrins are a ‘natural’ plant product, remember that ‘Natural’ does not mean safe. Many ‘natural’ flea products, including essential oils, limonene, garlic and pyrethrins have made many pet cats very ill.
Though perhaps a relatively poor flea contol product, pyrethrins are still very effective repellents for flies and mosquitoes, and fairly safe, too, if applied correctly
Also bad is the widespread use of pyrethrins in agriculture and its devastating effect on bees and other beneficial insects. Please be careful when using pyrethrins in the environment (like your yard), just because they seem relatively pet safe and degrade rapidly.
Ant killer (left) and wasp killer (right) containing pyrethrin, among another synthetic pyrethroid (tetramethrin in product on right). Kills bees well, too.
The Ugly: fortunately, there is not too much ugly about Pyrethrins.
Pyrethroids and synthetic pyrethrins, designed to combat fleas and ticks that show resistance to pyrethrins. These are in general much more effective poisons for fleas and ticks, and are used extensively today on some of the best flea and tick products available. Along with the synergist, many pyrethroids have a moderately good effectiveness against ticks and most fleas.
Product for dogs only that has some soothing aloe... possibly the aloe is the product that is actually doing anything to make the dog feel better?
This effectiveness pales in comparison with the newer and much safer products now on the market. There is still some degree of resistance, particularly in fleas, for most of these products (though it seems new synthetic pyrethroids are being invented all the time, presumably to keep ahead of the insects that are becoming resistant to them). Even with the synergist, Piperonyl Butoxide, in the mix, resistance is not futile. And these products have been around from the ‘dark ages’ before Imidacloprid, Fipronil and the rest were discovered, and we had lots of resistance problems with them. As I said earlier, even with these products, the battle against fleas was a constant and losing one.
similar products like this spot on Phenothrin were available dozens of years ago and they didn't seem to work great then, either. Phenothrin however is one of the newer synthetic pyrethrin toxins.
Many of these synthetic pyrethroids are not only highly toxic to fleas and ticks (and to fish), but to some of our pets as well. As an emergency veterinary clinician, I see a lot of poisonings and one of the most common we see are pyrethroid toxicities in both dogs and cats. Even big dogs come in toxic, often as a result of owner frustration and application of way too much product on the dog. Little dogs are sometimes toxic even from label doses of these products- we see Chihuahuas come in frequently with tremors from pyrethroid toxicity at the label dose, though I have yet to see one so ill I was concerned for its life.
Product with both pyrethrins and the synthetic toxin, pyriproxifen, which is to be used on dogs ONLY. Note there is no picture of a cat on this product.
Cat toxicity is by far the most common situation we are presented with, thanks to many owners’ inability to read labels that either say ‘Dogs Only’, or have a diagram of a cat with a slash through it (I have had several owners who swore they thought that cat diagram meant it was OK for cats!). Many of these cats are severely toxic, again due to massive overdose (I had one recently that was treated by the owner with the same product they put on their Rottweiliers). These cats often come in seizuring or violently tremoring, drooling, hyperthermic (secondary to seizures) and occasionally moribund (near death). So far (knock on wood) I have not lost a cat yet… but there were some close calls. The percentages I have found doing some on-line research states pyrethroid toxicities in cats result in death 10-25% of the time… yikes! Don’t use these! And read labels closely. These are our beloved pets that are being carelessly poisoned.
This slash through the cat is pretty tiny and many owners don't see it. The part about the product being potentially toxic or fatal if swallowed is highlighted, though. Why the part about not to use in cats is not highlighted as well, I have no idea.
Cats lack an enzyme in any decent quantity that detoxifies most synthetic pyrethroids. And cats have a habit of grooming off most things applied to their skin, adding to the somewhat mild toxic effect of these products by skin absorption. For this reason, I recommend NOT using these products on cats for any reason! Etofenprox is one synthetic pyrethroid that seems to be relatively safe for cats (at the proper dose only!) and I have little experience with how resistant fleas are to this product… but still, why use any of these poisonous products when there are so many highly effective and extremely safe ones on the market now? I don’t get it. While researching other products sold for flea control on cats, I discovered at least several products that had permethrin and phenonthrin, both synthetic pyrerthroids with a good deal of ‘cat toxicity’ to them. I assume the directions will guide owners in the ‘safe’ volume of product that can be applied to these cats? But my experience is that most products have very little in the way of detailed directions. I would recommend simply avoid these products completely.
above are two products containing the pyrethroid Etofenprox which, at the dosage listed for use on the package, is theorhetically safe for cats.
left is another flea spot on for cats with Etofenprox; for whatever reason, this product on the right, also containing Etofenprox, is for dogs and puppies ONLY... making me think that Etofenprox is only safe to use on cats as very specific concentrations
Untreated, overexposed pets can die of hyperthermia and brain damage from constant seizuring and tremoring, or directly due to respiratory failure from the nerve damage from the toxins.
Treatment for overexposure:
Pets we see that are overdosed with pyrethroids or pyrethrins should be immediately bathed to prevent further oral absorption of the product. Bathing is with cool water as warm water reportedly can increase the skin absorption of these toxins, which would otherwise minimal. Bathing with cool water can also help cool some of these violently tremoring or seizuring animals down.
Then these toxic pets are usually given some short acting anti-seizure medication injectably, such as Diazepam (Valium) or Midazolam (Versed), if they are having violent tremors or full on seizures. Following that, they are given and maintained on a muscle relaxant (Methocarbamol) or some other appropriate drug to keep them from overheating and make them more comfortable while their toxins wear off. This usually takes anywhere from 12 to 71 hours, but severe exposures can potentially last longer.
Mildly affected animals are also given activated charcoal to help absorb toxins still in the intestinal tract. Several affected pets may not tolerate an oral slurry like this and can inhale it, with dire consequences. So this treatment is not for everybody.
Most affected pets in my experience do well, but obviously severely affected pets, particularly cats, can die, especially if not treated early, according to poison control statistics. And fortunately, pets that recover, rarely if ever have any long term side effects.
Below are two national pet poisoning hot lines if you find yourself in such a situation.
Pet Poison Helpline: 800-213-6680
ASPCA Poison Control: 888-426-4435