Phenobarbital for Dogs With Seizures: What to Know
Key takeaways:
Phenobarbital is a relatively safe and well-tolerated treatment option for dogs with seizures. But your dog will need to have regular blood tests done while taking this medication.
Any phenobarbital side effects your dog experiences, such as increased appetite and thirst, will likely go away after a few weeks.
Phenobarbital can interact with other medications, such as certain antibiotics and antihistamines. Make sure you talk to your vet about your pet’s medications before giving them phenobarbital.
Table of contents
In dogs, a single seizure that passes quickly usually isn’t dangerous. But multiple episodes or very long-lasting seizures can be. If your pet has an average of two or more seizures per month, has a seizure that lasts longer than 5 minutes, or experiences a series of seizures within a single day, your vet will most likely prescribe them medication. While there are a few options, phenobarbital is a common first-choice option for treating seizure conditions in dogs.
Below, learn more about phenobarbital, including how it works, its side effects, and what medications it interacts with.
Phenobarbital for dogs at a glance
Common names | Phenobarbital |
What it treats | Seizures |
How it comes (forms) | Oral tablet, oral liquid, injectable liquid |
Common side effects | Increased appetite, increased thirst, weight gain, increased urination |
Average cost |
What is phenobarbital for dogs and how does it work?
Phenobarbital is a prescription-only anticonvulsant (anti-seizure medication) that is available as an oral tablet, oral liquid, and injectable liquid. Veterinarians use phenobarbital as an off-label medication since it is not FDA approved for use in dogs. Phenobarbital controls the electrical brain activity that happens during a seizure, helping to lower the number and severity of episodes.
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Phenobarbital is a controlled substance, meaning there are more restrictions regarding how your pet’s prescription can be filled at the pharmacy. These restrictions may include limits on the number of refills, the amount of medication you can fill at once, and how long the prescription is valid. The regulations vary from state to state, so check with your local pharmacy for details.
How is phenobarbital given to dogs?
Pet owners can fill a prescription for the oral tablets at any pharmacy. And some pharmacies offer compounded forms — such as pastes, oral liquids, or chewable tablets — for dogs who have issues swallowing pills. In a clinic or hospital, phenobarbital may be given as an injection.
You can give your dog phenobarbital with or without food. It should start working to fully control their seizures within a few weeks, although you may begin to notice some improvement sooner than that. It’s important not to suddenly stop giving your dog phenobarbital, as this can cause withdrawal symptoms, including a return of seizures.
How is a phenobarbital dosage determined for dogs?
Your veterinarian will determine your dog’s dosage based on a few factors, including their weight and the number and severity of seizures they’ve been having. Typically, phenobarbital is started at a dosage of 2.5 mg per kilogram of body weight every 12 hours. Depending on how your dog responds, their dosage may be raised or lowered.
What are the side effects of phenobarbital in dogs?
Phenobarbital is generally well tolerated once your pet adjusts to the medication. Your dog may seem more tired than usual or uncoordinated when first starting treatment with phenobarbital or if their dosage is raised.
Some dogs, however, experience the opposite effect and may appear more restless or nervous. You may notice them pacing around the room, panting, and whining.
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Other common side effects of phenobarbital for dogs include:
A higher appetite
Drinking more water than usual
Urinating more often than usual
Weight gain (typically caused by eating more food)
These effects are usually temporary and get better or go away within a few weeks after your dog starts treatment. If your pet still seems very sleepy or uncoordinated after taking phenobarbital for 2 weeks, talk to your vet, as they may need to lower the dosage.
Does my dog need to be monitored while taking phenobarbital?
Yes, your veterinarian will regularly test your dog’s blood to check their phenobarbital levels. The ideal phenobarbital blood level is between 15 μg/mL and 35 μg/mL. If a test shows higher or lower levels of the medication, your vet may change your dog’s phenobarbital dosage and retest them 2 weeks later.
Your dog’s liver health and red blood cell count will also be checked to monitor for the serious side effects discussed below. These blood tests will be done more often when your dog first starts taking phenobarbital. Once they are taking a steady dosage and responding well, the test will be done every 6 months.
What are the most serious risks of phenobarbital for dogs?
In rare cases, a dog may develop anemia (low red blood cell count) or have a sudden change in liver health while taking phenobarbital. These are serious side effects. If your dog has yellowing of the skin or eyes and is vomiting, contact your vet or go to an emergency animal hospital right away. These are signs of possible liver damage and care cause for immediate medical care.
Before prescribing phenobarbital, your vet may perform various blood tests to check your dog’s liver and kidney health. Vets do not typically prescribe phenobarbital to dogs with known liver, kidney, or breathing problems, as the medication can worsen these conditions or cause dangerous side effects. If needed, phenobarbital can be used in combination with other seizure medications.
Does phenobarbital interact with any other dog medications?
Yes, many medications interact with phenobarbital. Use phenobarbital with caution if your pet is taking any of the following:
Antibiotics, such as metronidazole and doxycycline
Antihistamines, such as diphenhydramine or cetirizine
Cannabidiol (CBD)
It’s important to note that these are not the only potential drug interactions for phenobarbital. Be sure to provide your vet with a complete list of all medications, vitamins, supplements, and herbal products your dog is taking before they start treatment. This will help your pet to avoid potential interactions.
What should you do if your dog misses a dose of phenobarbital?
Being consistent with your dog’s phenobarbital doses is very important, as missing even one dose can potentially trigger a seizure. If you forget to give your dog a dose and it’s almost time for their next dose, skip the missed one. Never give your dog two doses to make up for a missed one.
If you believe that your dog received too much medication, contact a pet poison hotline. Please note, a consultation fee may apply for the call.
What should you do if your dog continues to have seizures while taking phenobarbital?
Contact your vet immediately if your dog continues to have seizures after taking phenobarbital for 2 weeks. Seizures after this point may mean the dosage is not right or that your dog needs a different medication.
Your veterinarian may recommend you give your pet an additional dose after a breakthrough seizure, but you should only do this if your vet instructs you to. Giving your dog an extra dose on your own could be harmful to them.
It is helpful to keep a diary where you record the length of your dog’s seizures, their symptoms, and what happens right before and after their seizures occur. Consider taking a video of your dog when they have a seizure to share with the vet. This extra information may help your vet decide on the next steps for treating your dog’s seizures.
The bottom line
Phenobarbital is an anticonvulsant that can prevent seizures in dogs. It is generally well tolerated and a common first-choice treatment option. But there are side effects to watch out for, as well as several drug interactions.
Give your dog phenobarbital as instructed, and take them for any ordered blood tests on time. Be sure to keep a log of any seizures your dog has, and speak to your vet if you have any concerns about their behavior or how phenobarbital is affecting them.
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References
AKC Canine Health Foundation. (n.d.). Understanding canine epilepsy.
Brooks, W. (2021). Phenobarbital. Veterinary Partner.
Forsythe, L., et al. (n.d.). Phenobarbital. VCA Animal Hospitals.
Podell, M., et al. (2016). 2015 ACVIM small animal consensus statement on seizure management in dogs. Journal of Veterinary Internal Medicine.
Schamble, M. (2021). Phenobarbital for dogs with seizures. American Kennel Club.
Shell, L. (2015). Maintenance anticonvulsant or antiepileptic therapy. Merck Veterinary Manual.
