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My dog's phenobarbital side effects are worsening. What's happening?

Updated on September 23rd, 2025

Pet's info: Dog | Labrador Retriever | Male | neutered | 75 lbs

8 yr lab started phenobarbital 15 days ago. The effects of the drug appeared to be subsiding. Wobbly hind end, falling over on hind end. The last couple days they have seemed to get worse. He is dazed, panting, drooling, and still continues to fall over. on metacam as he does have arthritis in his hips. Is this still a reaction to the medication and the arthritis or am I looking at something more sinister. We have blood work on the 27th. Has had seizures since age of 3 just started more recently

2 Answers

Most Helpful Answer

Daniel Fonza, DVM

Answered By Daniel Fonza, DVM

Veterinarian

Published on July 18th, 2018

Hi there and thank you for using Petco Pet Education Center, formerly Petcoach to address your concern. In the initial stages of starting Phenobarbital, dogs develop what we call transient symptoms. These include becoming wobbly (ataxia), drooling, disorientation, panting, etc. These symptoms will eventually subside as the dog's body becomes used to the phenobarbital. If Trapper is no longer having seizures, I would call the veterinarian and ask if the dose can be slightly lowered. I hope this helps! Please let me know if you have any other questions or concerns and I would be more than happy to help you further.
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Related Answers from Veterinarians

  • Answered By Amy S. Eutsey, DVM

    Veterinarian

    Published on March 18th, 2020

    Hello. Typically, phenobarbital takes a bit of time to get used to. The average amount of time to see some effects is 4-6 weeks, but every animal is an individual case, so it can vary. Expected side effects would be drowsiness, excessive drinking and sometimes excessive hunger. If your pet is so drowsy that they cannot walk , eat or function relatively normally - I would suggest that you speak with your veterinarian about adjusting the dose. It can elevate liver enzymes. Usually, blood is drawn periodically to check the therapeutic levels. This helps determine dosage adjustments. If your pet has months in a row without a seizure, you may want to ask about lowering the dose. We try to achieve the lowest dose that is effective at controlling the seizure activity. Thank you for using Petco Pet Education Center, formerly Petcoach

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    1Pet Parents found this answer helpful

Smart Picks for Smart Questions

Health & Wellness
My dog is wobbly and sleepy on phenobarbital. Are these side effects?
Thanks for using Petco Pet Education Center, formerly Petcoach! Those are likely side effects from the phenobarbital. For that reason, I would highly recommend that you contact your veterinarian as they may decide to decrease his dose of phenobarbital based on this. Best of luck!
Updated on September 23rd, 2025
Vet Q & A
My epileptic dog is weak and drooling on phenobarbital. Is it normal?
It could be a very bad side effect of the phenobarbital, it is a strong medication that tends to cause severe side effects, especially if given at a loading dose in the beginning. you should contact your vet immediately in order to discuss possibly changing the dosage.
Updated on September 23rd, 2025
Health & Wellness
Dog on phenobarbital for seizures: lethargic, thirsty, wobbly. Normal?
Hi, thanks for using Petco Pet Education Center, formerly Petcoach! This is very normal in the first 2 weeks of starting phenobarbital. The dogs experience lethargy and the hind legs are wobbly and they appear to walk drunk. This will resolve in 2-4 weeks. The dogs do remain thirsty and have increased hunger on the medication. I wish Ceasar the best!
Updated on September 23rd, 2025
Health & Wellness
Why is my dog panting and unstable after starting seizure meds?
Thank you for submitting your question regarding Dusky. I am sorry to hear about her recent seizures. Most dogs will experience some side effects when first starting an anti-seizure drug. It can take a while for the dog's body to adjust to the medication. I suspect that is having the signs you have described from the phenobarbital. Her signs should resolve over several weeks. However, if she gets worse, has more seizures or does not seem to recover well from a seizure, then she will need to see her veterinarian. I hope this information helps!
Updated on September 23rd, 2025
Vet Q & A
Why is my dog pacing after starting phenobarbital for seizures?
The pacing could be a side effect of the phenobarbital or a side effect of the underlying cause for Frito's seizures. If the pacing continues or he has any decreased appetite, vomiting, or seems excessively sedate then you need to contact your veterinarian to discuss altering the dose potentially.
Updated on September 23rd, 2025
Health & Wellness
My dog had a seizure and is on phenobarbital. Is lethargy normal?
Hello and thank you for contacting Petco Pet Education Center, formerly Petcoach. Molly should take phenobarbital to avoid further seizures, which is a priority in this situation. You should continue with the dose she has been prescribed. Many dogs are lethargic after the first few doses of phenobarbital but then are back to normal. Please, get in touch with your vet on Monday to confirm that Molly is on the right dose of phenobarbital. If the lethargy and lack of appetite persists, your vet will likely decrease the dose or change the medication. Molly will probably stay on anti-seizure medication for life.
Updated on September 23rd, 2025
Training & Behavior
My dog on Phenabarbitol has incontinence & hind end issues. What to do?
I wish I had a little more information to help you with this question. IF she is just starting the medication and is on a loading dose then she could just be pretty drunk from the medication and may improve in time as her body adjusts. However, if she has been on the meds for a while and these are new changes then I would be concerned that this may be part of her underlying neurologic problem and not due to the meds. Regardless, I would encourage you to follow up with your veterinarian soon. In the meantime if you have other questions I would encourage you to request a consultation for more direct question and answer and “discussion” format. Best of luck and thank you for using Pet Coach.
Updated on September 23rd, 2025

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