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Author: Subject: Pyrethrins Causing Seizures?
wackyvorlon
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[*] posted on 14-5-2009 at 09:13
Pyrethrins Causing Seizures?


I've run across some discussions recently of pet owners claiming that exposure to pyrethrins caused seizures in their pets. I've been reading up on these compounds, but I don't understand exactly how it can lead to seizure. My understanding is that it interferes with the sodium ion channels in the neurons. Intuitively, it seems to me that toxicity from it would cause an effect almost like sedation.

I've read up on organophosphates, and their mode of action(inactivating acetylcholinesterase) leads to a pretty intuitive understand of the effects of toxicity. I was wondering if anyone might be able to explain what's happening? Is this being caused by pyrethrins, an adjuvant or something completely unrelated? Any thoughts are greatly appreciated! Thanks.
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chemoleo
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14-5-2009 at 16:28
Arrhenius
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[*] posted on 16-5-2009 at 23:15


Pyrethroids are almost always used in combination with piperonyl butoxide as a synergist. I would guess this has something to do with the toxicity, since piperonyl butoxide is a covalent P450 inhibitor. Cats have very interesting metabolism, which is drastically different than humans. I think they are lacking in esterases and glucuronidases, if I recall. While pyrethroids are virtually non-toxic to us, I too have heard of the cat problem.

This is an interesting, though relatively basic article. Maybe you've already read it.

Dymond NL, Swift IM. Permethrin toxicity in cats: a retrospective study of 20 cases AUSTRALIAN VETERINARY JOURNAL (2008); 86:219-223.

"It decreases sodium movement through cell membranes, thus suppressing potassium conduction, which inactivates the action potential, resulting in repetitive nerve
firing because depolarisation does not occur. These actions on the presynaptic nerve endings lead to the adverse clinical signs seen in permethrin toxicosis."
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wackyvorlon
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[*] posted on 17-5-2009 at 06:51


Excellent! Fortunately, I'm with Athabasca U and they have a subscription:) Looks like this journal has a couple of interesting articles about it. Thanks!
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[*] posted on 17-5-2009 at 07:18


Some of the more recent flea and tick topical medications for dogs now contain pyrethrin as a repellent. It seemed to have a bad effect on my sister's dog, so she washed it off and got a refund from the vet. It wasn't seizures, but the dog was acting weird. He got better a few hours after it was washed off.

I used one on my dog a couple years ago. Didn't really affect her much, but there was a heck of a lot more of it and it matted down her fur on her back. So I switched back to the kind without pyrethrin.
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Arrhenius
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[*] posted on 17-5-2009 at 15:10


It does seem peculiar to me that pyrethroids are used in this manner. There's really no question that they're fantastic pesticides (when used properly) and are highly effective at killing insects. But that it's a reasonable treatment to dose an mammal systemically with pyrethroids in order to kill ecto parasites seems strange.

How are these products applied? Is it drops applied to the back of the neck? Do you use the same amount if it's a great dane or a chihuahua?
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wackyvorlon
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[*] posted on 17-5-2009 at 15:50


They show up in flea collars and flea baths.
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GoatRider
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[*] posted on 17-5-2009 at 17:16


Quote: Originally posted by Arrhenius  
How are these products applied? Is it drops applied to the back of the neck? Do you use the same amount if it's a great dane or a chihuahua?

Drops along the back. And it comes in different sizes based on the size of the dog. But it's about 2 or 3 times as much as the non-pyrethrin formulas, so you get a grease mark that's at least 3 times as big.
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[*] posted on 17-5-2009 at 17:34


The systemic drops we use (Advantage) contain imidacloprid which is a chloroneonicotinate, not a pyrethroid. Although the detox pathway is less efficient in cats, all 12 of ours seem to have few if any side effects.

We do half-dose the smaller ones (<10 lb).

We have noticed interesting behavior when there is a current flea infestation. The application of the systemic is followed by what appears to be shakiness and wobbling. What this is, in fact, is the cat reacting to the multitude on dying (hence moving around, A LOT) fleas. No doubt that this must itch like hell.

When all the fleas are moving at once, the cat freaks out, wrinkles it's skin, shakes it's legs, etc. trying to shoot them off (not unlike when a piece of tape is stuck to one of its feet).

Once the fleas are dead, the cat returns to its normal (albeit less amusing) state. The systemic Capstar (nitenpyram, another neonicotinoid analog) pills are even more entertaining.

Cheers,

O3




[Edited on 18-5-2009 by Ozone]




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Arrhenius
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[*] posted on 17-5-2009 at 19:32


Interesting! I would have thought neonicotinoids might have greater tox issues in a systemic application.

In reading the paper I posted, it's somewhat shocking that this pyrethroid issue in cats is fairly common. The paper is a case study of 20 cats that were admitted to a single vet clinic over the period of ~1 year. That seems like a lot to me.
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