What Is Phenobarbital?
Phenobarbital is a drug that veterinarians use to treat dogs having seizures. The drug is categorized as a barbiturate. Your vet may give it to your dog if they have epilepsy or other causes of seizures. This drug stabilizes their brain cells and prevents abnormal electrical discharges in the brain that cause seizures. It’s also sometimes used as a sedative for dogs.
Phenobarbital is a human drug that is used "off-label" to treat dogs and other animals. It's important to understand its uses for your pet and to follow your veterinarian's instructions carefully.
Why Do Dogs Get Seizures?
The most common cause of seizures is epilepsy, which is an inherited disorder passed down through genetic material. It’s not very common, but certain breeds are more likely to have it, including:
- Bernese Mountain Dogs
- Border Collies
- English Springer Spaniels
- Pembroke Welsh Corgis
- Boxer Dogs
- Cocker Spaniels
- Siberian Huskies
- Collies
- Dachshunds
- Golden Retrievers
Other causes of seizures in dogs are:
- Liver disease
- Kidney failure
- Brain tumors
- Brain trauma
- Toxins
Symptoms of Seizures in Dogs
Seizure patterns and symptoms can vary from dog to dog and also from one type of seizure condition to another. Still, seizures tend to progress in stages and dogs often share these symptoms and behaviors:
Preictal phase (pre-seizure aura). Much like with humans, dogs may start behaving differently minutes, hours, or even days before they have a seizure. It may seem like they sense that something is up. The most common red flags that you may notice as an owner include restlessness, anxiousness, and irritability. Your dog may refuse to leave your side or stalk off and hide somewhere in the house. Whining, shaking, and drooling are also typical.
Ictal phase (seizure). The seizure itself can last anywhere from a few seconds to several minutes. Focal seizures are sometimes so subtle they can be easy to miss. During one of these episodes, your dog may seem dazed or zoned out, they may tremble, salivate, start barking or biting at nothing, or have trouble balancing. Generalized seizures, on the other hand, are in-your-face obvious. Dogs typically collapse, become unconscious, and their legs and body jerk erratically. They often lose control of their bladder and their bowels. If a dog stays in a full-blown seizure for more than five minutes, this is referred to as status epilepticus or prolonged seizure, which can be life-threatening.
Postictal phase. Right after a seizure, your dog may seem confused or disoriented. They may pace, salivate, seem particularly thirsty, or pee more than usual. Some dogs, about 10%-17%, may temporarily lose their vision. Post-seizure symptoms can last a few minutes or as long as 24 hours.
Phenobarbital for Dogs
Seizures can damage your dog's brain, especially if they happen for too long or frequently. They can also be fatal. Your dog might also suffer a fall or other accident during a seizure. Your dog may accidentally bite during a seizure. Seizure control is necessary but has to be weighed against the side effects of the drugs.
Many dogs have only one seizure or infrequent seizures. They may not benefit much from daily anti-seizure medication given for months or years. Your veterinarian will start such medication if your dog:
- Has a brain lesion such as a tumor, or has had a brain injury or brain disease
- Has two or more seizures in a six-month period
- Has prolonged seizures (lasting more than five minutes)
- Has seizures that occur in a cluster (three or more seizures in one 24-hour period)
Phenobarbital is one of the most preferred anti-seizure medications for dogs. It has a long record of safety, and the cost of therapy is less than other drugs.
How Does Phenobarbital Work?
As a barbiturate, phenobarbital prevents or reduces the frequency of certain types of seizures in people and animals. It’s also used to treat anxiety and to bring on drowsiness, for instance, before a medical procedure. Phenobarbital works by slowing nerve activity in the brain. Doctors and scientists think it does this by enhancing GABA, a natural brain chemical that controls nerve cell activity and has a calming effect.
Phenobarbital Dosage for Dogs
The typical dosage of phenobarbital for dogs is 2-4 milligrams per kilogram of your dog’s weight. It is given orally twice a day.
Give your dog phenobarbital only under the guidance of your veterinarian. The dose has to be tailored to your dog based on blood tests. This is because your dog may be metabolizing phenobarbital faster or slower than normal. Blood level measurement helps veterinarians find the best dose for your dog.
Regular monitoring via blood tests is important. The timeline for this can vary from vet to vet, but an example schedule might be:
- Two weeks after starting phenobarbital
- Two weeks after changing the dose
- Every 6 to 12 months when medication is working
Phenobarbital Side Effects in Dogs
Since phenobarbital is a drug that acts on the brain, it can have side effects that impact your dog's nervous system and affect their behavior and coordination. Especially when your dog starts taking it, you might notice that they are sleeping or lying around more than usual. They may also be somewhat clumsy, tripping and bumping into doors and furniture.
It’s very common for side effects to get milder as your dog’s body adjusts to the drug. In case of non-life-threatening side effects, don’t stop giving your dog their medication without first contacting your vet. Based on bloodwork and seizure control, they may decide to reduce your dog’s dosage as opposed to stopping or changing the drug altogether. If you believe your dog is having a severe reaction to this drug, contact your vet immediately or take them to an animal emergency room.
Common side effects
- Low energy and sleepiness
- Increased thirst and urination
- Increased hunger
- Elevated liver enzymes
- Diarrhea
- Hyperactivity
- Excitability and anxiety
- Clumsiness
Possible side effects
- Vomiting
- Itching
- Liver damage
- Pancreatitis (inflammation of the pancreas)
- Decreased blood cell counts, including anemia
- Aggression
Aggressiveness and hyperactivity
Because phenobarbital has a sedative effect, dogs can become calmer, less fearful of strangers, and may even be easier to train when they are on this medication. Sometimes, phenobarbital can have the opposite effect, making dogs hyperactive or aggressive toward people and other animals. If this happens, contact your vet immediately.
Liver damage
Phenobarbital can raise your dog’s liver enzymes. In some cases, long-term use of the drug can lead to scarring of their liver and liver failure. Your vet will order occasional lab work so they can monitor your dog’s response to the drug. Be sure to keep these appointments because if there are any red flags your vet can change your dog’s treatment and avoid potentially permanent liver damage.
Phenobarbital withdrawal effects in dogs
Phenobarbital can cause physical dependence, which means that your dog could experience physical withdrawal symptoms. If you stop the drug all at once or wean them off too quickly, your dog could have “barbiturate withdrawal seizures.”
Can All Dogs Be Treated With Phenobarbital?
Phenobarbital is a first-line drug when a dog needs to be treated for seizures. It’s been used for many years, is affordable, and is generally well-tolerated. However, some health conditions make phenobarbital a no-go or a drug that should at least be used with caution. These include:
- Allergy to phenobarbital
- Liver disease
- Kidney disease, infection or inflammation
- Heart disease
- Lung disease or severe breathing problems
- Anemia
- Adrenal gland problems
- Pregnancy or nursing
- Hypovolemia (any condition causing high fluid loss, such as dehydration)
Can Human-Use Phenobarbital be Used for Dogs?
In the past, there hasn't been a version of phenobarbital specifically made for dogs. So, vets prescribe phenobarbital that is made for human use. This common and widely accepted practice is called prescribing a drug “off-label.”
Since 2021, the U.S. FDA has granted conditional approval for two drugs for treating idiopathic epilepsy (seizures without a known cause) in dogs. The two medications are Fidoquel-CA1 (phenobarbital tablets) and KBroVet-CA1 (potassium bromide).
Conditional approval means that the drug makers have shown that these medications are safe, manufactured according to standards, and expected to be reasonably effective. But the drug companies have not completed all the studies they need for official FDA approval. Once a company gets conditional approval, it is allowed to market the drug and has five years to show evidence of the medication’s effectiveness and safety to gain full FDA approval.
The conditionally approved phenobarbital specifically intended for dogs is not generally available at this point. So, vets still prescribe human-use phenobarbital. That said, you should never give human-intended phenobarbital or other drugs to your dog without specific instruction from a licensed vet. Dosages may not be the same, and you could put your pet at risk.
Phenobarbital Alternatives for Dogs
Phenobarbital is a go-to maintenance medication for dogs with seizure disorders. But it’s not the answer in all cases. Some health conditions, such as liver disease, can make it a less-than-ideal option. Some dogs continue to have seizures while on the drug. But there are other options that your vet might prescribe instead of phenobarbital or in addition to it to make seizures less frequent or less severe.
They include:
- Bromide (potassium or sodium salt)
- Clonazepam
- Felbamate
- Gabapentin
- Levetiracetam
- Mephenytoin
- Primidone
- Topiramate
- Valproic acid
- Zonisamide
Takeaways
Once you start your dog on phenobarbital, keep a log for the first few weeks of any side effects you notice, if they are getting milder or worse, and if and when your dog has any breakthrough seizures. Share this information with your vet at follow-up visits and don’t hesitate to call if you are concerned about your dog’s reaction to the drug at any point. With careful medication management, phenobarbital can help your dog with a seizure disorder live a long and happy life.
Phenobarbital for Dogs FAQs
Will phenobarbital calm my dog down?
Because phenobarbital has a sedative effect, dogs can become calmer, less fearful of strangers, and may even be easier to train when they are on this medication. But sometimes, phenobarbital can have the opposite effect, making dogs hyperactive or aggressive toward people and other animals.
Why is my dog on phenobarbital and still having seizures?
It can take a few weeks for phenobarbital levels in your dog’s blood to reach the point where they can effectively control seizures. Once they are on the right dose of phenobarbital and receiving the drug regularly with no missed doses, some dogs will have few to no seizures. That said, studies show that less than half of all dogs can stay completely seizure-free without side effects. If your dog has what are known as “breakthrough seizures,” your vet may raise their dose, switch them to another medication, or add another seizure drug to their daily regimen. If their seizures don’t fully respond to any combination of drugs, the most realistic goal may be reducing the frequency and severity of their seizures rather than preventing them.
Is phenobarbital used to put dogs to sleep?
Phenobarbital is not intended for euthanizing (putting down or putting to sleep) dogs and other animals. However, it is often confused with pentobarbital (also called sodium pentobarbital), another barbiturate and sedative that is sometimes used to treat uncontrollable seizures and is also a preferred drug for euthanasia.
What is the success rate of phenobarbital in dogs?
Research suggests that when dosed correctly and given regularly, phenobarbital reduces the frequency of seizures in as much as 85% of dogs with idiopathic epilepsy (seizures without a known cause). That can make life enjoyable and relatively peaceful for a whole lot of dogs and their owners. However, less than half of dogs with idiopathic epilepsy are completely seizure free without side effects while on phenobarbital. In some cases, vets will switch medications or add another drug to a dog’s daily regimen to achieve better seizure control and minimize potential phenobarbital risks.
Is phenobarbital harmful to dogs?
Phenobarbital is a first-line drug when a dog needs to be treated for seizures. It’s been used for many years, is affordable, and is generally well-tolerated. It does have side effects, but most are not life-threatening and tend to get milder as your dog adjusts to the drug. In some cases, phenobarbital can have more harmful effects. It can lower blood cell counts, cause inflammation of the pancreas, raise liver enzyme levels, and over time cause irreversible liver damage or even liver failure. Your vet will order occasional lab work so they can monitor your dog’s response to the drug. Be sure to keep these appointments because if there are any red flags, your vet can change course in your dog’s treatment before any permanent damage is done.
How long does phenobarbital last in dogs?
Phenobarbital has a long elimination half-life, which means that it takes a while for your dog’s kidneys and liver to clear the drug from their system. The advantage of this is that phenobarbital can stay in your dog’s bloodstream at stable levels for an extended time and generally only has to be given every 12 hours (twice a day).
