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Dr. Kara
Dr. Kara, Board Certified Veterinarian
Category: Veterinary
Satisfied Customers: 16888
Experience:  Over 20 years of experience as a veterinarian.
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I gave my cat a flea treatment this morning and ever since

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I gave my cat a flea treatment this morning and ever since then he's been acting weird. Normally, he follows me around like a dog. But now, he'll walk a couple of steps and then stop, sit down, and just stare into the distance. When he get up, he shakes his hind legs like he has leg cramps or something. When he sits or lies down, he doesn't seem to get comfy. He doesn't curl up into a ball with his tail wrapped around him like normal; he lies on his stomach with his tail straight out behind him and doesn't put his head down all the way. Could this be some sort of reaction to the flea treatment?

My cat is 7 or 8 years old and is an inside cat.

Hello, I'm Dr. Kara. I have over 20 years of experience as a veterinarian and I'd like to help with your concerns about your kitty and the flea treatment that you applied today.


It is possible that his symptoms could be related to the flea topical that was applied.

Some of the over the counter flea topicals can cause the symptoms that you are seeing, especially if they contain chemicals from the pyrethrin family of insecticides as cats are especially sensitive to that group of chemicals.

I do need a little more information from you.


What topical did you use?

What are the active ingredients listed on the side?

Have you ever used this product before? If so, how long ago and what was his reaction then?

Can you still see a greasy area where it was applied?

Is he healthy otherwise or is he dealing with some chronic health concerns?

Was his skin at all red or broken or scabby before the medication was applied?

Is his skin at all red now where the medication was applied?

Has he had any muscle tremors?

Is he eating and drinking normally?

Is he able to eliminate normally?

Have there been any other changes for him?


Thanks for your patience with all my questions, the answers will help me give you the best advice.

I see that you went offline.

I am concerned about your kitty so I will give you some general recommendations.


In case he is reacting to the flea medication you need to bathe him fully in cool water and a degreasing agent such as Dawn dishwashing detergent.

Do not vigorously rub the area, as that will increase absorption. But do gently bathe that area to remove as much as possible. The less he absorbs the better. If you can still see where the medication was applied concentrate on getting that area clean. You may need to bathe him several times.


If this is a pyrethrin based product common symptoms of this toxicity are drooling, nausea, diarrhea, dilated pupils, tremors, incoordination and in very severe cases seizures.

The problem with this toxin is if they cannot eat and drink they get very dehydrated and worsen quickly.

If the tremors are very bad they can cause an increase in body temperature and muscle toxins which can cause brain damage and kidney failure.

So if their body temperature rises and they are tremoring consistently we put them on fluids to bring down the body temperature and flush out the muscle toxins.

If actual seizures occur he will need intravenous medication for that.


At home all that can be done is decontamination (bathing) and nursing care.

That includes keeping him quiet and away from stairs so he doesn't fall and hurt himself, and helping him eat and drink. Keep an eye on body temperature.(concern is a rectal temperature more than 103.5F) Keep him in a quiet area as the more he is stimulated the more he will tremor.

If he seizures he must be seen by a veterinarian.

There is nothing that you can do at home for that.


As far as how long his symptoms will last, that will depend upon whether we can get most of this off or not.

Usually symptoms last 2 to 3 days if we can get most of the product off.

If this is an extreme exposure then symptoms can last a couple weeks.

Very rarely there is long term damage.


Please let me know if you have any further questions.

Customer: replied 4 years ago.

Hi Dr. Kara,

(Yes, sorry. My husband got home from work and so I was explaining my worries to him. Below are the answers to the original questions you asked!)


The product I used was Hartz UltraGuard Pro. The active ingredients listed are (S) Methoprene ( 3.6%) and Etofenprox (40%).


I've never used this product--or any other flea product--on him before. But I found fleas on him, which were probably brought into the house on my or my husband's clothes after a day of yardwork, so I decided to treat him.


Yes, there's still a greasy area at the application site.


No, the skin wasn't broken or irritated or red prior to application. (At least not to my knowledge.) There's no redness and nothing unusual about the site now, either.


No muscle tremors, just the shaking or flicking of the back legs when he starts to walk.


He is definitely eating normally! I've seen him. :-) I haven't actually seen him drink, but I don't always see that.


Not 100% sure yet about elimination. I changed his litter this evening in order to determine that.


He's a normally perfectly healthy cat, although he is an aggressive groomer.


The other other changes in addition to what I've mentioned are that he also keeps licking his back paws, especially between his toes. Also, he's nowhere near as cuddly and affectionate as he normally is. He's just really quite "off" in terms of personality. Definitely zoned out.


FYI, I applied the product about 12 hours ago. Please let me know if, based on the above, you still think I should bathe him.



Thanks very much for the further information.

Methoprene is an insect growth regulator. It is used to stop flea eggs and larvae from developing and has no effect on mammals

Etofenprox is from the pyrethrin family of insecticides. It is supposed to be safer for cats, but I try never to use any pyrethrins in cats because they are so sensitive. I think he is reacting to that.


If you can see a greasy spot it is well worth trying to remove as much of the product as possible. So yes, I absolutely recommend bathing him with a degreasing soap like Dawn dishwashing soap.


Because he is a big groomer he may have ingested some of the product and that increases toxicity.


His aggressive licking of his rear paws may also signify an allergic type reaction, either to the pyrethrins or the carrier that moves the product through the haircoat into the oil glands. That's another reason to bathe him.


Knowing that he may be having an allergic reaction I also recommend Benadryl

(diphenhydramine only, the combination products with decongestants and acetaminophen are toxic to cats) at 1mg to 2mg per pound every 8 hours. That's a half of 25mg tablet every 8 hours for a cat that is 8 to 15 pounds. You may need to use this for a week or two while waiting for the allergic reaction to resolve and the product to dissipate. Antihistamines can cause sedation but that effect should wane with repeated use.


You will need to watch his skin very, very closely, especially where the product was applied. Some cats will get burn like lesions where the product was applied and the skin can ulcerate.


His foot flicking can be due to an allergic type burn or tingle or it may be affecting the nerves to his rear legs making them tingle or not work normally. These effects should pass with time.


In the future the only flea topicals I would recommend are Frontline Plus or the Advantage products. They are more expensive, but they are safe and do not contain pyrethrins. I never recommend Hartz or Sargeants products.

Please let me know if you have any further questions.

Dr. Kara and other Veterinary Specialists are ready to help you
Customer: replied 4 years ago.
OK, thanks. I have Dawn, so I'll try getting the gunk off.

I normally wouldn't use Hartz, either, but I was desperate. The closest store to our small rural town is a big box store (name is not important) and that's all they carry.

I just hope my awesome kitty will be ok!

I understand that sometimes we have to do the best with what we have available.

The good news is that in most cases pyrethrin toxicities and reactions are transitory, and by removing as much of it as we can he should recover faster. He is still eating and that is a very good sign.

I would expect that he will be back to himself in a few days, and almost surely within a week or two.

I'll check in with you in a few days to see how things are going but feel free to reply back to me if you have any questions in the meantime. Thank you for the positive rating, much appreciated, Dr. Kara.

Customer: replied 4 years ago.

Hi again,

I was able to get my kitty in to the vet today. He said it was good that I washed off the topical given the symptoms. Thanks for your advice to do so!

He is no longer doing the leg-flicking thing today and is not restless. Yay!

However, the vet noticed that his pupils are dilated and are not going all the way back down to their normal size. That's definitely not normal for my cat. My vet believes that it's a reaction to the flea treatment and that it should clear up in a day or so.

He also gave my cat a cortisone shot to help with the itching and the pulling out of hair. Tonight my kitty is deeply sleeping. It's almost a frighteningly deep sleep. I hope it's either a reaction to the shot or that's he's just exhausted from all he's had to endure the past couple of days!

Thank you for the update on your fellow.

I am pleased to hear that his leg-flickering has dissipated. Dilated pupils are another sign of pyrethrin toxicity, and I do expect that to resolve as well as the levels of toxins decrease in his body. Dilated pupils can also be a sign of stress and we certainly know your poor guy was stressed, so again they should go back to normal as he feels more himself.

I am glad that he received relief via a cortisone shot as well. While antihistamines can help cortisone is much faster, and he sounds like he needed more immediate relief.

I think his deep sleep tonight is more related to all the stress he went through yesterday and all of his muscle twitches and spasms then any sort of reaction to the toxin. Your poor guy finally got some relief and given his exhaustion he is likely to sleep quite deeply tonight. As long as he is eating and drinking normally, and continuing to improve, I would not worry too much.

Keep in touch and let me know how he does, but so far I am pleased with what you have told me, Dr. Kara.

I'm just checking in on your fellow to see how he is feeling after his reaction to Hartz UltraGuard Pro.
Please feel free to let me know if you have any questions or concerns or if things are progressing well I'd love to hear that as well.
Thank you, Dr. Kara.
Customer: replied 4 years ago.

Well, he was doing very, very well. But then this evening he vomited and then had a seizure. It's the first seizure we've witnessed, so we don't know if he's had others. The seizure lasted about 10 or so seconds. After it, he stumbled around as if he were drunk.

Just a few minutes later, he seemed almost normal again.

Fortunately, our vet has after hours emergency service. My husband took our kitty in, and they gave him some IV fluids and ran bloodwork. Blood and vitals were all normal, which is good. They believe the seizure was a delayed reaction to the toxins.

I feel like a horrible cat mommy. :-(

I'm so very sorry to hear that he had a seizure, of course that is very upsetting for you.

I think that you would have seen some evidence of previous seizures (vomit, drool, things knocked over or disheveled) even if you weren't home when he had them so this may be his only one.

It is true that pyrethrin toxicity can lower the seizure threshold and cause seizures. The good news is that his blood tests were normal so there doesn't look to be any sign of permanent organ damage.

If he has more seizures your veterinarian may choose to put him on an anti-convulsant medication like phenobarbital while we wait for the toxin to clear. Hopefully he won't have any more or if he does he will only need to be on medication for a few months.

I'm so sorry, you aren't a bad pet owner, you just a very sensitive fellow and you didn't know it. If I had my wish these products wouldn't even be on the shelf.

Customer: replied 4 years ago.

Our vet gave us some diazepam (valium) in case he seizes again.

It's just so concerning to me that he seemed fine and then this happened. It's been several days after the flea treatment.

I, too, wish these products were not sold.

I understand your concern but the neurologic system is a very strange and sensitive thing. I suspect that what he absorbed before you bathed him thoroughly has built up in his central nervous system irritating it. As it dissipates he should go back to normal but it appears he will be one of those cases that take weeks to months for that to happen rather then the usual days to a couple weeks.

I'm glad that you have something on hand if he seizures again, I hope that it won't be necessary.

Customer: replied 4 years ago.

Hello Dr. Kara,

I'm just wondering what your opinion is about Vectra. That's what my local vet sells for flea/tick prevention. After everything that we went through last week, I feel hesitant to put anything on my kitty!

Nervous Kitty Mom

Hello, I understand your concern about applying anything to your kitty given the reaction he had to the Hartz product.


The good news is that Vectra does not contain any chemicals in the pyrethrin family.

It has an adulticide (Dinotefuran) and an insect growth regulator (Pyriproxyfen). There have been some reports of tremors and muscle spasms with Dinotefuran use in cats but the percentages are very low, especially compared to pyrethrin toxicity numbers in cats.


I tend to recommend Advantage II for cats with known sensitivities as I have heard of very few side effects with it and yet it is still a very effective product. Just my personal preference, and you might want to discuss this further with your veterinarian as they know your kitty well and saw the problems he has had recently.