If your dog has been diagnosed with epilepsy, your veterinarian may prescribe phenobarbital. This drug is a barbiturate that is used to control seizures in dogs. It is effective in preventing or stopping seizures, but it can also cause some side effects. In this blog post, we will discuss the benefits and risks of phenobarbital for dogs.
What is phenobarbital and what does it do for dogs with epilepsy?
Phenobarbital is a barbiturate drug that is used to control seizures in dogs. It is approved for use in Canada, the UK and Australia for the treatment of epilepsy in dogs.
Phenobarbital is generally regarded as a broad-spectrum anti-convulsant as while it is a GABA receptor agonist in the central nervous system, it also inhibits glutamine and calcium fluxes within neurological synapses. The phenobarbital molecule is similar to the human neurotransmitter gamma-aminobutyric acid (GABA), which binds to GABA receptors in the brain. This binding action causes phenobarbital to have a depressant effect on the central nervous system and adjusts the seizure threshold.
How effective is phenobarbital for dogs in preventing seizures?
Phenobarbital for dogs is very effective in preventing seizures. Phenobarbital has been used as either a stand-alone or adjunct anticonvulsant in dogs for long-term seizure management or emergency seizure management, depending on the situation and the individual animal.
After intravenous (IV) administration, phenobarbital distributes into the brain within 10-15 minutes. Intravenous administration is most often used in veterinary hospitals to control severe or life-threatening seizures.
When given orally, phenobarbital is rapidly absorbed and reaches peak blood plasma levels in 2-4 hours. The rate of absorption is slower when taken with food, therefore, veterinarians recommend that phenobarbital for dogs be taken on an empty stomach.
Phenobarbital for dogs is metabolized by the liver and the half-life varies, ranging from 24-72 hours. Therefore, the recommended dosage is every 12 to 24 hours, and it will take about 7-14 days to reach a consistent level of phenobarbital in the dog's system (steady state).
In dogs, phenobarbital drug levels often decrease even when the dose is constant. This happens because of a combination of things: enhanced metabolism from enzyme induction, and weight gain from increased appetite. Of all the anticonvulsants currently used, phenobarbital has the most evidence to support its efficacy in dogs. The main reasons veterinarians turn to other drugs are adverse side effects and tolerance to phenobarbital (which makes it less effective over time).
What are the side effects of phenobarbital for dogs?
The most common phenobarbital side effects in dogs are:
- Increased appetite
- Increased thirst and urination
- Sleepiness or lethargy (transient effect after starting phenobarbital)
- Unsteadiness when walking (ataxia)
- Depression
- Disorientation
- Aggression (uncommon but can occur)
Occasionally, and when high doses of phenobarbital are used, respiratory depression can occur. This means phenobarbital can slow down the breathing rate and make it shallow. If you think your dog is having trouble breathing, it is important to seek emergency medical care.
Phenobarbital may also cause your dog's liver enzymes to increase. The increase in liver enzymes may not be indicative of a problem, or it may represent hepatopathy caused by phenobarbital. Your veterinarian will likely perform liver function tests before starting phenobarbital and then periodically while your dog is taking it to check for any changes.
In some dogs, phenobarbital may cause pancreatitis (inflammation of the pancreas). When used for extended periods, phenobarbital for dogs can result in elevated levels of fat within the blood (hyperlipidemia), which is a risk factor for the development of pancreatitis. Common clinical signs of pancreatitis in dogs include vomiting, anorexia and abdominal pain.
When should phenobarbital not be used in dogs?
Phenobarbital should be avoided in dogs with cardiovascular disease, respiratory diseases such as asthma, myasthenia gravis, and other health conditions that might lengthen the effects of phenobarbital.
Additionally, dogs with liver disease should not take phenobarbital because the liver is responsible for metabolizing and excreting phenobarbital from the body. If your dog has any pre-existing health conditions, be sure to talk to your veterinarian before starting phenobarbital.
What are the important drug interactions of phenobarbital for dogs?
Phenobarbital may interact with other drugs your dog is taking, including other anticonvulsants, sedatives, steroids, and heart medications. Be sure to tell your veterinarian about all the drugs and supplements your dog takes before starting phenobarbital.
The following medications may have their efficacy decreased due to the induction of hepatic enzymes by phenobarbital and other barbituates:
- Anticoagulant medications
- Beta-blockers
- Chloramphenicol
- Corticosteroids
- Doxorubicin
- Doxycycline
- Estrogens and progesterones
- Metronidazole
In some cases, phenobarbital is used concurrently with levetiracetam for the management of seizures in dogs. Phenobarbital for dogs increases the metabolism of levetiracetam, so the levetiracetam dose may need to be adjusted and increased when phenobarbital is added.
How to administer phenobarbital to your dog?
The most common form of phenobarbital to be used at home is oral tablets. There are a variety of strengths available making it easy to find the right phenobarbital dose for your dog's weight. Most dogs will require twice-daily dosing, although some dogs may require only once-daily dosing. As absorption and effect will decrease if given with food, phenobarbital should be given on an empty stomach, at least one hour before or two hours after a meal.
When giving phenobarbital to your dog, it is important to follow your veterinarian's instructions and use only the phenobarbital product prescribed for your dog. Never give phenobarbital (or any other medication) to your dog without first consulting with your veterinarian.
Phenobarbital for dogs is a controlled substance and requires a phenobarbital prescription from a licensed veterinarian. Phenobarbital tablets should be stored in a tight, light-resistant container at room temperature and out of reach of children and pets. Dispose of unused phenobarbital products according to your veterinarian's instructions or the directions on the package.
Tips for managing your dog's epilepsy with phenobarbital
- Work with your veterinarian to find the phenobarbital dose that is right for your dog. The phenobarbital dose may need to be adjusted as your dog's weight changes or if other medications are added.
- Be consistent with dosing times and never skip a dose.
- Try not to give phenobarbital with a full meal
- If you miss a dose, give it as soon as you remember. If it is almost time for the next dose, skip the missed dose and continue with the regular dosing schedule. Do not give two doses at once.
- When first starting phenobarbital in your dog, make sure your veterinarian has prescribed a loading dose, but in small increments to limit the occurrences of respiratory depression
- Store phenobarbital tablets in a tight, light-resistant container at room temperature and out of reach of children and pets.
Can I stop giving phenobarbital to my dog?
If you are considering stopping phenobarbital, please talk to your veterinarian first as sudden discontinuation of phenobarbital can cause an increase in seizure activity. A slow, gradual tapering off of phenobarbital is necessary to avoid withdrawal seizures. While it depends on the duration of use, most veterinarians recommend a 25% dose reduction every month.
How often should you perform blood tests to monitor phenobarbital levels in your dog?
Phenobarbital blood levels should be checked every six to twelve months in dogs that are on phenobarbital long-term for seizure management. Blood tests may need to be done more frequently if your dog's phenobarbital dose is changed or if your dog has any other health changes.
Can phenobarbital be used alongside other anti-convulsant medications?
Phenobarbital can be used as either a single agent or in combination with other anti-convulsant medications. If phenobarbital is being used alongside other anticonvulsants, it is important to monitor the blood levels of all the medications your dog is taking to ensure that they are within the therapeutic range. Levetiracetam (Keppra), potassium bromide (KBr) and zonisamide can be used in conjunction with phenobarbital when necessary.
How long does it take for phenobarbital to work in dogs?
When first starting phenobarbital, it can take up to two weeks to reach a steady state in the central nervous system. Steady-state means that phenobarbital levels in the brain remain constant and at a therapeutic level. Once phenobarbital has reached a steady state, it will continue to work for seizure control as long as it is given at the correct dose.
Does phenobarbital for dogs cause aggression?
While it is uncommon, phenobarbital can cause aggression and hyperactivity in some dogs. If this is noticed, talk with your veterinarian about phenobarbital alternatives or a phenobarbital dosage change.
In conclusion, phenobarbital for dogs is a drug that has various effects on the body, including reducing seizures, inducing sleep, and depressing respiration. It works by inhibiting certain electrical signals in the brain and spinal cord and also enhances the inhibitory effect of another neurotransmitter called GABA. At high doses, phenobarbital can also reduce nerve transmission at muscle junctions. phenobarbital can be an effective tool in managing your dog's seizures but it's important to work with your veterinarian to find the right phenobarbital dose and to monitor blood levels regularly.
Phenobarbital can cause side effects like increased appetite, thirst, and urination in most dogs when they first start the medication. Phenobarbital is a medication that needs to be tapered off slowly to avoid withdrawal seizures so if you are considering stopping the drug, please talk to your vet first.
We hope this article was informative and helpful. Phenobarbital can be a great tool in managing seizures but it's important to be informed about the risks and side effects before starting your dog on phenobarbital. Thanks for reading!