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Rare Phenobarbital Side Effects in Dogs – One Dog’s Story

kartoffel treatment plan

TL;DR – if your dog is recently on phenobarbital and has symptoms such as a suppressed white blood cell count and autoimmune issues (something that looks like an allergic reaction) then phenobarbital may be the cause. Read on for more details of my story and check out the comments below for others.

Phenobarbital is a very common prescription drug used to control seizures in both humans and pets. It’s almost always the very first medication your vet will recommend if your dog is diagnosed with epilepsy, due to the very low cost of the prescription as well as it generally being viewed as a safe drug as it has been in use for over 100 years.

That being said, there are still very rare cases where phenobarbital has incredibly dangerous side effects to your pet, and unfortunately my dog, Kartoffel, suffered from side effects for months before we realized phenobarbital was the cause. In fact, it’s possible he could have needed a bone marrow transplant or even had to be put down if we waited much longer.

The purpose of this article is to share our story, because I wasn’t able to find anything like this documented online when I was looking for possible causes of Kartoffel’s health issues. To be clear though, this is NOT me making a case against phenobarbital or suggesting you don’t listen to your veterinarian. This is meant to be a list of things to watch out for if your dog is starting phenobarbital or has been on phenobarbital for some time, and is having strange, maybe seemingly unrelated health issues.

Part 1: Kartoffel Has Seizures

kartoffel laying
Kartoffel lounging around the time of his first seizure

This saga all starts back in June of 2017. As I was getting ready for bed, Kartoffel came upstairs and gave my wife a strange look seemingly knowing something was wrong. A few seconds later he collapsed to the ground and started have a seizure – his first ever, around 4 years of age.

After a frightening minute or so the seizure passed and Kartoffel exhibited amnesia after his seizure – something he has done after every seizure to date. This is something else I haven’t found any information on, so I’ll describe it a bit here in case it’s helpful to others.

After his seizures, he wakes back up and looks lost and scared. He clearly has no recognition in his eyes as to where he is or who we are. So he starts barking and isn’t too keen to let anyone near him! As a 110lb+ dog, this can be alarming it it’s own right though I’d say he doesn’t cross the line into aggression.

These amnesia episodes last anywhere from 30-90 minutes before he snaps back to himself. I haven’t found any surefire ways to get him to regain his memory faster, sometimes it seems like letting him sniff me works but not always. If you know of something that could help, let me know in the comments!

Moving on, after the first seizure we took him to the emergency vet, had bloodwork done and had him stay overnight in case he had more. At this point we weren’t sure if it was epilepsy, a brain tumor, something he ate, etc and other than an expensive brain scan there’s no good way to narrow down the possible cause other than to wait and see if it happens again.

Somewhere in the neighborhood of 8-10 weeks later, Kartoffel had another seizure. This time between seizures meant it’s very unlikely to be a brain tumor (good!) and very likely that it’s canine epilepsy (boo!).

So we got him started on phenobarbital sometime in mid to late August (as best I can remember), which hopefully would reduce his seizures to 2-4 times a year, or maybe even less. There’s no real “standard” for what kind of change you can expect from seizure medications, only that they should occur much less frequently than if left untreated.

Part 2: Unknown Phenobarbital Side Effects

It wasn’t too long after Kartoffel was on his daily dosages of phenobarbital that the side effects started coming. The first thing I can remember is that he started getting raised bumps on his snout. They were under the skin/fur, did not move, and were somewhat hard. We took Kartoffel to the vet to get looked at, and the diagnosis was it was some sort of allergic reaction. Possibly to something he got into outside, flowers/trees, etc.

He was given a cortisone shot which would suppress his immune system response (this is an important trend) and the bumps went away shortly. If my memory is correct they may have came back once more, another shot was given, and they were not seen again before we got him off of phenobarbital.

Another issue he was having was a red, bulging left eyeball. It was like his eyeball was inflamed and reddened which he was also taken to the vet for and also diagnosed as some sort of allergic response. He got more cortisone, allergy pills, and eye drops but nothing seemed to truly fix the problem. This ended up being another strange side effect of what phenobarbital was doing to his immune system.

Part 3: Admission to the Emergency Hospital

kartoffel at emergency hospital

In mid to late November, things finally came to a breaking point. Kartoffel had been developing some weakness in his legs that we thought was part of the sedation of the phenobarbital, but one morning Kartoffel struggled to even stand and I knew something was very wrong. I made a same-day appointment for the vet and after observing his weakness they had a blood test done.

This is what was most shocking and really raised the alarm. A normal white blood cell count for a dog is between 6,000 to 17,000. Kartoffel’s white blood cell count was ~450 – lower than most dogs going through chemotherapy. This could only mean his immune system was having serious issues and basically not functioning. His bone marrow was not producing the white blood cells his body needed to fight infections and carry oxygen through his blood stream. His muscle weakness? Likely a lack of oxygen reaching the muscles.

I’m lucky enough to live within 15 minutes of a full-scale emergency veterinary hospital complete with an internal medicine and neurology department, so I left my regular vet and took him in to be admitted.

After talking with an internal medicine specialist, she determined that the phenobarbital could be the culprit. It seems the drug was somehow toxic to his body and damaging his bone marrow, or preventing it from functioning properly. We had to get a bone marrow biopsy done on him, which involved putting him under anesthesia and taking a sample from a bone in his shoulder.

The biopsy results came back and determined that his bone marrow looked “different” but still functional, which was great news and also seemed to confirm the new diagnosis. The new treatment plan was as follows –

  • Ween Kartoffel off of phenobarbital onto a new seizure medication (Potassium Bromide)
  • Keep Kartoffel on some serious doses of Prednisone for months (to suppress his immune system’s reaction from attacking his bone marrow/white blood cells)
  • Give Kartoffel antibiotics for several weeks as his body can’t fight off any infections with such a low white blood cell count.
  • A handful of other drugs I don’t remember the purpose of, see below!
kartoffel treatment plan

After 3 nights of being admitted to the hospital (total charges came to around $4,000 for this stay – I’ll be considering pet insurance for future dogs!), Kartoffel was released to us to come back home.

Part 4: The Aftermath and Today

I can’t remember the exact timeline of when Kartoffel completed his transition to the new medication and got off everything else, but eventually his blood cell count was back to normal and has remained normal since. After switching to Potassium Bromide he had two seizures about 10 weeks apart, but at the time of writing we’re on a streak of roughly 4 months with no seizures!

March 2019 update – still no seizures, getting close to a year now I believe. We bumped him down from 2500mg to 2000mg a day and his energy has gotten a lot better since then as well.

kartoffel happy dog

Today Kartoffel seems to not have any real lingering issues from the whole ordeal he went through, but I really wish we could have got him off of phenobarbital sooner since it was harmful to him.

If your dog is starting phenobarbital I would not be overly concerned – millions of pets and humans take the drug every year for seizure treatment and have no serious side effects. However if your dog starts having seemingly random auto-immune issues that appear as allergic reactions, talk to your vet about keeping a close watch on their blood cell counts and consider if it might make sense to switch medications if symptoms continue.

4 thoughts on “Rare Phenobarbital Side Effects in Dogs – One Dog’s Story

  1. I’m so happy to find this article! Our dog is going through a very similar experience. We believe the phenobarbital was causing her anemia and bone marrow suppression. But unfortunately she isn’t recovering, she has been off the phenobarbital for 10 weeks and her numbers haven’t improved but actually gone down. Our vet has hesitated putting her on prednisone but I think I will push for it now after reading your story. Thank you

    1. Best of luck, the Prednisone is no walk in the park for a dog either. Kartoffel got “pred-head” which is where the jaw muscles that run to the top of his head atrophy and you’re left with a very goof, pointy-headed dog! Eventually his pred-head got better once he got off the medication but he had some hind leg weakness as well. It was a tough time but at least his blood levels got back to normal eventually.

  2. I just wanted to thank you because finding your story might have saved my dog, Maevis. She was started on phenobarbital in February and before starting all her blood work was normal two weeks ago she lost her appetite and started acting lethargic my vet’s really good and listens when I think something’s wrong and ran a full blood panel. She was severely anemic and her white blood cell count was very low they did x-rays and an ultrasound checking for internal bleeding and they couldn’t figure out anything they hospitalized her over the weekend and kept her on an IV and start her on immune suppressant for an autoimmune disease she had a very small initial Improvement so she got to go home but that initial improvement declined again a couple of days later. the vets had no idea what was causing it or how to help her. they sent her blood smear to a pathologist in town which we haven’t received the results yet, the next step is a bone marrow biopsy. the vets didn’t think it had anything to do with phenobarbital because her liver values were still good but I was searching online and I came across what you had written and I called my vet and asked her if it was a possibility she said she’d heard of it causing anemia in extremely rare cases but not a decrease in white blood cell count I told her about what I had read and she said she would do some research of her own the next morning she called me back and said that none of the vets in her practice had seen a dog have a reaction like that but that she did find some extremely rare cases like yours and we took her off phenobarbital this last Friday.  she had blood work checked this morning and her white blood cell count has improved quite a bit her red blood cell count went a little lower but her vet thinks that with this response it very possible was the phenobarbital. She said it could take up to three months before she gets back to normal values if it was the phenobarbital but I finally feel like there’s a little bit of Hope. Her appetite is starting to get a little better, shes still lethargic but seems a little more herself this morning. Through all the research I did this was the only thing that I found that led me to believe it really could be the phenobarbital and without it the vets would still be looking for some kind of an an answer and I’m not sure how longer she could have kept going or how I could have come up with any more funds so i cannot put into words how thankful I am that you chose to share your story. My dogs are like my babies and it would kill me to lose her thank you so much.

    1. Thanks for sharing Whitney, this is exactly why I wrote the article. My regular vet could not find anything wrong and did not think that the Phenobarbital could be the issue as none of the vets at the practice had heard of this scenario. I’m fortunate enough to have a large Emergency Vet nearby which has specialty departments with more expertise/experience which led us to the root cause.

      she had blood work checked this morning and her white blood cell count has improved quite a bit her red blood cell count went a little lower but her vet thinks that with this response it very possible was the phenobarbital

      I recall something similar (if not this exact scenario) with one of Kartoffel’s blood tests shortly after getting off Phenobarbital so I think you’re on the right path. Best of luck!

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