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Pexion ®


Back To Epilepsy Article


Ron Hines DVM PhD

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February, 2016

One of my European dog-owning clients placed her epileptic pet on Pexion recently. I had no experience using it and my USA Boehringer Ingelheim representative told me that he knew of no plans at the moment to introduce the product to the North American market. That seemed rather unusual to me since the US/Canadian veterinary pharmaceutical market is the most lucrative in the world. It is also ironic because the drug's anti-epileptic qualities were discovered through NIH-funded studies. Those studies (aimed at developing the medication for human epileptics) were suspended when it was found that the drug affected smokers differently than non-smokers. But dogs (and mice) were used in the testing and the researchers took note that although it was somewhat less powerful in its anti-epileptic effects, it seemed to work well in them. Pexion® is marketed as having less potential to cause side effects in your dog than phenobarbital and recent studies in Europe confirm that. When compared to long term phenobarbital use, Pexion/imepitoin cause less thyroid gland supression. Although it did not adequtely control seizures in some dogs, the majority significantly improved as their time taking the medication increased. (ref pg 446)

Pexion (imepitoin) was origninally called AWD 131 138 . (ref) Here are some other key references on this medication: 1, 2, 3

Pexion/ Imepitoin is one of a class of drugs called Imidazolinone derivatives. These drugs are also known to be anxiolytic . That is, like Valium (diazepam), they are calming. So at higher doses or in highly susceptible individuals they might change a dog's behavior in variable ways. The Royal Veterinary College in London is looking into that. (ref)

A co-author of one of the key imepitoin studies theorized to me that the German studies submitted to the EMA might need to repeated to obtain FDA approval (It is commonly thought that FDA drug approval standards are the most demanding in the world [ref]). Perhaps there just isn't a large enough market for the drug to justify that added expense - I really do not know. Never-the-less the drug is catching the attention of American veterinarians. (ref)

If your epileptic dog was receiving phenobarbital but is now taking Pexion® or if it was the first drug tried, I would appreciate your observations and feedback. Email me and I will post your observations here.

April 9, 2016

I write after reading your website regarding Pexion use.
I am a Vet Dr from the UK who recently have started
practicing in Oregon. I am on the lookout for starting to
use Pexion, but there seems to be little or no evidence for
FDA pending approval.

I can confirm my previous experience has been by and large

Out of all patients I started on Pexion, about:
1/3rd improved vs pentobarbital
1/3rd remained the same
1/3rd had increased frequencies of relapses into seizure activities.

I really wish this drug would be available as an alternative
to the hepatotoxic current market leader.

Kind Regards,

Veterinary Surgeon


June 15, 2016

I'm the owner of Spud, a little silky terrier in Australia. Late last year, at the age of 5, he started having unexplained seizures. They were quite significant seizures and he started with one tremendous one on a very hot day, then went on to have 2 the following week and another 2 the week after that in the same day. He had always been healthy and was a dog with a very big, cheeky and playful personality. When he was diagnosed with epilepsy I was so worried about medication altering his personality that I considered not medicating [him at all] and monitoring him to see how he would cope. But due to the severity of the seizures my vet strongly advised medication as a trial for a few months.Spud started on Pexion. He hasn't had a seizure since. He gets a little bit dopey for about an hour after it's been administered, but then he's back to his usual self.
It's been brilliant. His liver is great too. I highly recommend this medication. It's reasonably pricey, but my little Spud is still my little Spud. He's not doped up and is healthy and seizure free!

K. M.


February 17, 2017

About the Pexion :................I live.My dog (17kg staffy cross) developed idiopathic epilepsy at the age of two and a half.  She was on phenobarbitone [phenobarbital] for a couple of years (and remained fit free) with blood tests every six months.  Given the possibility of long term liver damage, my vet suggested a change to Pexion.  She is now 7 years old and has had no fits on Pexion. (200mg twice daily) She seems to tolerate it well and apart from a little sleepiness (which she also had with the phenobarb) there have been no side effects that I can discern.

I’m not sure why they won’t let dogs have Pexion in the US because the reason my vet changed my dog over from the phenobarb was to reduce any future health problems.  And as I said, as far as I can tell, she’s pretty much side effect free, and that’s after being on the Pexion for a bit over a couple of years.  For your info, her seizures were cluster fits…the first time it happened she had about five short (relatively mild) fits within around three quarters of an hour.  (this was in the middle of the night, and fearing brain tumours and worse, I rushed her to an emergency vet)  She was initially treated with Valium until all the various tests were done, ruling out any underlying diseases, and then put on the phenobarb.  After about 18 months (after discussing with my vet) we took her off the phenobarb, to see if she might be one of those very few dogs who get over their fits, but within a few days she had more fits, so it was back onto the phenobarb.  And then, after some time, on to the Pexion.

Also for your info, in case it’s at all relevant to you, the Pexion costs around $700 (Australian) a year.  That’s more expensive than the phenobarb was, but overall only about $100 more per year given that the vet considers it unnecessary at the moment to have the twice yearly blood tests (for liver) that were required on the phenobarb. I hope that’s of some use to you.

C.M , Sydney, Australia


March 21, 2017

Hi, tonight we commenced our Radar on Pexion. So far several hours later, it would seem minimal reaction to medication !