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Starting Phenobarbital for Dogs with Epilepsy

Updated: Apr 10

Dr. Natascha Hedegaard BVetMed MRCVS graduated as a veterinary surgeon from the Royal Veterinary College, London, in 2018. She is passionate about optimising canine health with a holistic approach to veterinary medicine and consideration for the individual patient .She is currently undertaking her Postgraduate Certificate in Small Animal Medicine with an aim to becoming an Advanced Practitioner.

Starting Phenobarbital for Dogs with Epilepsy


If your dog has been diagnosed with epilepsy, phenobarbital is the most commonly prescribed first-line anti-epilepsy medication. As a pet parent, it's natural to have questions and concerns about starting phenobarbital for dogs with epilepsy. In this blog post, we'll provide you with valuable insights and tips to help you navigate the journey of phenobarbital treatment for your dog's seizures.

Understanding Phenobarbital

Phenobarbital is a commonly prescribed medication for the management of seizures in dogs. Veterinary brand names in the UK include Epiphen, Epityl, Phenoleptil and Soliphen. Phenobarbital belongs to a class of drugs called barbiturates, which work by stabilizing abnormal electrical activity in the brain to reduce the frequency and severity of seizures. Phenobarbital is usually given as tablets but a liquid form is also available. It has good efficacy in most dogs when given twice daily.

Phenobarbital is rapidly absorbed by the body after ingestion orally. It reaches peak concentrations in the blood within 4-8 hours. A steady level in the bloodstream is not reached however until 7-10 days after starting the medication.

Who shouldn't have Phenobarbital?

The following contraindications are standard for Phenobarbital but please ensure you have a thorough conversation with your veterinarian about your pet's overall health and lifestyle to ensure this is the best option for them:

  1. Animals with significant liver disease or reduced liver function

  2. Pregnant animals

  3. Nursing bitches

  4. Animals with respiratory problems


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What to Expect If You Do Start

Starting your dog on phenobarbital can be a process that requires patience and careful monitoring. Here's what you can expect during this time:

  1. Initial Dosage: Your veterinarian may start your dog on a low dose of phenobarbital and gradually increase it until the seizures are adequately controlled. This process allows your veterinarian to find the optimal dosage for your dog while minimising potential side effects and allowing your dog to adjust to this strong medication . Every dog responds to medication differently and your veterinarian will take into consideration any concurrent problems (e.g. liver disease) prior to deciding the specific plan for your pet. It doesn't matter whether you give Phenobarbital with food or not but please ensure you give it as close to twelve-hourly as possible and please do not stop suddenly without veterinary guidance as this can lead to withdrawal-seizures.

  2. Monitoring: Regular monitoring is essential to assess your dog's individual response to phenobarbital and detect any potential side effects, including changes to the liver. Your veterinarian will recommend periodic blood tests to measure the medication's concentration in your dog's bloodstream and ensure it remains within the therapeutic range. The dose required to control seizures varies greatly between individuals as every individual processes the drug differently.

  3. Potential Side Effects: Phenobarbital can cause side effects in some dogs, especially when starting treatment or when adjusting the dosage. Common side effects may include:

  • Sedation or lethargy

  • Ataxia (loss of coordination), wobbliness

  • Increased thirst and urination

  • Increased appetite or weight gain

  • Hyperexcitability has been reported in dogs who are under-dosed

  • Rarely, superficial skin lesions have also been reported. Please contact your veterinarian immediately if any such changes are suspected.

  • Elevated liver enzymes

It is essential to report any unusual symptoms or changes in behaviour to your veterinarian promptly.

Potential Side effects

Sedation and Coordination Issues: At the onset of therapy, after dose adjustments, or when combining with another drug like bromide, your pet may experience sedation and poor coordination. Typically, these effects diminish within the first week unless higher doses are used. If they persist or become severe, your veterinarian might recommend reducing the phenobarbital dose or trying a different medication.

Increased Urination and Drinking: Phenobarbital can act as a diuretic, leading to increased urination and thirst in your pet. Ensure your furry friend always has access to water while on phenobarbital to prevent dehydration. Some pets on higher doses may have accidents indoors or drink excessively.

Increased Appetite: Phenobarbital therapy can boost your pet's appetite, but they may not actually need more food. Weight gain can become an issue, so consider feeding a lower-calorie diet to allow your pet to eat more without packing on the pounds. Extending meal times with devices like a puzzle feeder can also help manage appetite.

Liver Health: Liver damage is a known concern with anti-epileptic drugs, but it's relatively rare. In some cases it can be as soon as 2 weeks into treatment but more frequently occurs when higher doses are used chronically. Phenobarbital is metabolised in the liver, which can suffer damage during this process. This can occur if your pet is unusually sensitive to the drug, has pre-existing liver disease, or if given excessively high doses over time. Routine blood tests are performed before and during treatment to monitor liver function. Please note that changes to some of the enzymes may not correlate with actual damage to the liver therefore your veterinarian may recommend more specific testing if concerned (such as a dynamic blood test known as Bile Acid Stimulation Test, an ultrasound or CT of the liver and/or liver samples to be taken).

Pancreatitis: Chronic use of Phenobarbital can increase fat levels in the blood which can put them at risk of pancreatitis, which is inflammation of the pancreas. Symptoms include vomiting and loss of appetite, and in severe cases, it can be life-threatening. Multiple factors contribute to this condition, including obesity, high triglyceride levels, a fatty diet, scavenging behavior, and high doses of phenobarbital combined with bromide.

Blood Cell Abnormalities: While rare, phenobarbital may disrupt blood cell production or cause destruction. Changes including neutropenia, anaemia and thrombocytopenia may occur. If you notice any unusual symptoms in your pet after starting phenobarbital, contact your veterinarian promptly for further evaluation and guidance.

Please contact your veterinarian if you have any concerns, uncertainties or have noted any of the above signs that your pet may not be tolerating the medication trial well.


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Long-Term Management

Once your dog's seizures are under control with phenobarbital, they will likely need to continue taking the medication for the rest of their life. It's crucial to adhere to your veterinarian's prescribed dosage and schedule to maintain seizure control and prevent recurrence.

Here are some tips to help you support them through the process:

  1. Administer Medication Consistently: Give phenobarbital to your dog at the same time(s) every day, as directed by your veterinarian. This helps maintain steady blood levels of the medication for optimal seizure control.

  2. Monitor for Side Effects: Keep an eye on your dog for any signs of side effects, and notify your veterinarian if you have any concerns. Prompt identification and management of side effects are essential for your dog's well-being.

  3. Stay in Communication with Your Veterinarian: Maintain open communication with your veterinarian throughout the treatment process. They can provide guidance, answer your questions, and adjust the treatment plan as needed to ensure the best outcome for your dog.

  4. Be Patient and Persistent: Achieving optimal seizure control with phenobarbital may take time and adjustments to the dosage. Be patient and trust your veterinarian's expertise as you work together to manage your dog's condition.

Conclusion: Starting Phenobarbital for Dogs with Epilepsy

Starting your dog on phenobarbital for seizures may feel overwhelming at first, but with the right information and support, you can help your furry friend live a happy and comfortable life. By staying informed, vigilant, and proactive, you can navigate the challenges of phenobarbital treatment with confidence and provide the best possible care for your beloved companion.

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