Side Effects Of Phenobarbital In Dogs

Medical review by K9 Healthcare Council of America (K9HCA). Intended for educational purposes only. Always seek medical advice from your veterinarian.

Phenobarbital For Dogs

As a pet owner, watching your dog have a seizure is incredibly frightening!

You’re witnessing your dog go through a very traumatic experience and you feel out of control–unsure what to do to help them.

When an animal has a seizure disorder, the frequency and severity of the seizures determines the need for treatment.

In dogs, the prescription barbiturate Phenobarbital is probably the first choice to suppress seizures. It’s effective, safe if used responsibly, reasonably priced, and conveniently dosed, all of which makes it a popular choice.

But there are side effects of phenobarbital in dogs.

Since treatment with phenobarbital to manage seizures is generally life-long, periodic monitoring of your dog’s blood is highly recommended.

What Is Phenobarbital for Dogs? 

Phenobarbital is one of the most commonly used drugs to treat epilepsy and other seizure disorders in dogs.

It is known by the brand names Luminal Sodium, Barbita, Solfoton® and Tedral®. Alternative generic names are: phenobarbitone, fenobarbital, phenemalum, phenobarbitalum and phenylethylbarbituric acid.

Phenobarbital (sometimes abbreviated as Pb or Phb) is one of the medications most commonly used to treat seizures in dogs because of its low cost and effectiveness in 60 to 80% of dogs with Idiopathic Epilepsy.

While Pb is not approved for use in animals by the Food and Drug Administration (FDA), it is still one of the first choices for veterinarians and its use is accepted as an off-label or ‘extra-label’ drug in clinical practice.

Phenobarbital is classified as a Schedule IV controlled substance & therefore requires a prescription available only through a DEA-licensed veterinarian.

side effects of phenobarbitol in dogs
Phenobarbital is a barbiturate drug with anticonvulsant properties that can have mild to severe to potentially lethal side effects in dogs.

In addition to being used on a daily basis to prevent seizures, in some instances, Phenobarbital can be used to stop seizures in progress.

Phenobarbital For Seizures in Dogs

Phenobarbital is generally effective for control of canine seizures regardless of the underlying cause of the seizure disorder, which means that is can be used for epilepsy, brain tumors, infectious diseases, or toxic poisonings.

Although Phenobarbital is used regularly in small and large animals to treat seizures or as a sedative for ‘off label’ applications; in these instances, follow your veterinarian’s directions and precautions very carefully as their direction may be significantly different from those on the product label.

Phenobarbital can be used as a lone therapy or along with other natural therapeutics like Cannabidiol (CBD) to decrease the frequency and severity of your pet’s seizures.

Side Effects of Phenobarbital in Dogs

While generally safe and effective when prescribed by a veterinarian, phenobarbital is a barbiturate that can cause serious side effects in some animals.

Phenobarbital inhibits seizures by decreasing the activity of neurons–unfortunately, this effect is not specific to the neurons involved in causing the seizures but also affects other neurons in the CNS as well.

Many of the potential adverse reactions of this drug are caused by this unintended side effect on other neuron pathways in the brain.

Common Side Effects of Phenobarbital in Dogs

Usually if a pet is going to experience side effects from phenobarbital it happens in the first few weeks of starting the medication or when the dosage is increased.

Adverse effects associated with phenobarbital in dogs include restlessness, anxiety, lethargy, depression, increased appetite and increased thirst.

Excessive urination, excessive thirst and excessive hunger are the 3 most common long-term side effects of phenobarbital on dogs.

Side Effects of Phenobarbital Include:


The goal of seizure therapy is to end the seizures, not sedate the patient. Most patients will not show noticeable sedation while on phenobarbital and if they do, there is a good chance the dose is too high. Some patients cannot find an effective dose of phenobarbital that is not sedating, and these patients may need a different medication, or simply a reduction of the phenobarbital dose and addition of a second medication.

Sedation During Initial Therapy

It is not unusual for some patients to appear depressed or sedated when phenobarbital therapy is begun. This effect is generally temporary and resolves as the patient gets used to the medication. If this problem has not resolved after two weeks, a blood test can determine if the dose is simply too high and needs to be changed.

Excessive Appetite

Phenobarbital makes patients very hungry. This can be problematic if the patient becomes obese or overly focused on food.

Excessive Thirst

It makes patients thirsty. This could become a problem if the patient drinks so much water that house-soiling becomes a problem.

Other side effects can also include lethargy, hyperexcitability, ataxia (loss of coordination or hind end weakness) and night-time restlessness. Most of these side effects diminish or disappear after the first few weeks of therapy.

Holistic Dog Care By K9 Medibles

Although short-term side effects typically clear up after the first few weeks your veterinarian will have to monitor your dog for long-term side effects if they take the drug for an extended period of time.

Other potential long-term adverse effects of Phenobarbital:

  • Lethargy / Sedation
  • Anxiety / Restlessness
  • Loss of coordination
  • Weight gain
  • Anemia
  • Liver damage

If you see concerning side effects in your dog, then consult your veterinarian, as they may wish to alter the dosage or seek an alternative form of treatment.

Dogs with Addison’s disease, kidney disease, respiratory problems, or existing liver disease should not be given this drug. Make sure your veterinarian is aware of any medical conditions your dog has, as well as any other medications your dog may be taking, as these can react poorly with phenobarbital.

As with almost all drugs, there is a risk of allergic reaction that can lead to anaphylaxis, a life-threatening condition. Contact your veterinarian right away if your dog has trouble breathing, starts sneezing, breaks out in hives, or shows other allergy symptoms.

Side effects such as incoordination may indicate a dose that is too high and needs to be adjusted accordingly.

Although rare, a more serious side effect of phenobarbital is liver disease.

If signs of liver dysfunction, known as Icterus, (yellow coloration of gums and skin) are observed or if you notice vomiting, anorexia, skin ulcers or liver enzymes that are 4-5 times higher than normal on bloodwork, then a different medication should be started immediately, and phenobarbital discontinued (see caution of discontinuing use below).

Phenobarbital side effects in dogs
Phenobarbital side effects. Chronic exposure to phenobarbital can lead to scarring in the liver and liver failure that can be irreversible.

Phenobarbital For Dogs Dosage

Because absorption, distribution and speed of metabolism can vary among dogs, published dose recommendations only serve as a general guide.

Most new patients are started at the lower end of the dose range; however, patients with frequent or severe seizures are often best managed by starting at the higher end of the dose range or by using a ‘loading’ dose.

The initial starting dose that is frequently used is 2 mg to 3 mg per kilogram of body weight every 12 hours. Your veterinarian will adjust this dosage based on blood levels, documented seizure activity and side effects of the medication.

Your veterinarian will also tell you how often to give your dog his/her medicine. As a general rule, Pb is given every 12 hours and should be given as close to every 12 hours to avoid seizures.

Some manufacturers use grams and some use grains as a unit of measure. In milligrams, Phenobarbital is available in 15 mg, 30 mg, 60 mg or 100 mg tablets.

Manufacturers who use grains offer 1/8 grain (8 mg), 1/4 grain (16 mg), 1/2 grain (32 mg) or 1 grain (65 mg).

How Much Phenobarbital Can a Dog Take?

Phenobarbital comes in liquid or tablet form and is available both from a veterinarian and from a regular pharmacy by prescription.

When Phenobarbital is started, it takes 1 to 2 weeks to reach a stable blood level. Phenobarbital is easily taken up into fat tissue so it can be given with OR without food.

In tablet form Phenobarbital is given 2-3 times daily. Phenobarbital’s peak activity occurs 4-8 hours after the pill is given, but during the initial period when stable blood levels are achieved it cannot be fully relied upon to prevent seizures.

Based on your dog’s response (positive & negative) the dose may be increased up to 8 mg per pound (16 mg/kg) per day.

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects.

Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.

Phenobarbital For Dogs Overdose

At high dose levels, phenobarbital is a sedative and can result in nervous system depression, coma and death.

In addition to the numerous adverse effects mentioned above, Phenobarbital may be habit forming. Tolerance and psychological and physical dependence may occur with continued use.

Use prudence and an abundance of caution when giving Phenobarbital to pets with Addison’s Disease, kidney disease, liver disease, respiratory abnormalities, or anemia. Phenobarbital may interact with other drugs so it’s best to consult with your veterinarian if your pet is on other medication.

Although uncommon, with chronic exposure, Phenobarbital can lead to liver toxicity, scarring in the liver and liver failure that can be irreversible; potentially leading to a lethal conclusion.

Liver toxicity is associated with prolonged high phenobarbital blood levels, but regularly scheduled monitoring tests can head off such an event in plenty of time to change medication.

Phenobarbitol for dogs overdose
Do not use phenobarbital in pets that are allergic to it or that have kidney inflammation/infection, severe breathing problems, or severe liver disease. It should be used cautiously in pets that are anemic, dehydrated, have poor adrenal function, or heart/lung disease and in pets that are pregnant or lactating.

What happens if I overdose my pet on Phenobarbital Tablets? 

Seek emergency veterinary medical attention if you think you have given your pet too much Phenobarbital. An overdose on Phenobarbital can be fatal. Signs of an overdose may include loss of appetite, vomiting, trouble breathing, jaundice, sedation, and coma.

What happens if I miss giving my dog a dose of Phenobarbital?

It is very important to never miss a dose–missing a dose may cause your pet to have a seizure. Try very hard to keep on a regular schedule.

If you miss a dose, give the missed dose as soon as possible. But if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses!!

Discontinuing Therapy – Tapering Phenobarbital

The decision to stop Phenobarbital must be made very carefully; but it’s reasonable to consider with dogs that are seizure-free for one to two years or for dogs who are having side effects that negatively affect their Quality of Life.

It is important not to withdraw the medication suddenly.

Sudden barbiturate withdrawal can cause a serious seizure episode known as status epilepticus. Essentially, status epilepticus is a seizure that does not end. It is a life-threatening situation that requires immediate veterinary care to save your pet’s life!

If phenobarbital needs to be discontinued, it should be withdrawn slowly by gradually decreasing the dosage over a period of months.

The dose should be gradually tapered off over a period of about 6 months. If the dog has developed liver disease, the reduction can be by as much as 25 % a week.

It is important not to discontinue phenobarbital cold turkey as doing so may precipitate severe seizures. Your veterinarian can instruct you on how to wean off phenobarbital. If there is no urgency, some vets suggest a reduction of 10% every week or so.

The major risk of discontinuing drug therapy is seizure recurrence, which is most likely to happen during withdrawal or within several months of stopping therapy.

Natural Alternatives to Phenobarbital for Dogs with Seizures

Treatment alternatives to phenobarbital are available for dogs who develop liver disease or where you wish to reduce the Pb dosage–OR–you prefer to incorporate a more natural method to control seizures.

CBD-rich hemp oil has been shown to reduce the frequency and duration of seizures in dogs & can even be used in conjunction with phenobarbital use in dogs as an added measure of protection against neurological damage caused by seizure activity.

CBD works in dogs by interacting your pet’s Endocannabinoid System (ECS). This system is responsible for regulating several processes within your dog’s body, including appetite, mood, sleep, pain, immunity and digestion, to name a few.

CBD oil can be used to reduce the frequency of seizures and even interrupt them as they are happening, with little to no side effects.

When your pet takes hemp CBD oil, it interacts with the ECS, causing it to work more effectively. The result is multiple positive changes in your animal’s health, as well as the overall regulation of homeostasis of your dog’s body.

Aside from treating epilepsy, CBD can also reduce a dog’s anxiety, improve their mood, bring back their appetite, treat conditions like glaucoma and IBD, and lower the pain levels of conditions like arthritis and hip dysplasia.

Most dogs have a healthy reaction to CBD supplementation, and even those that don’t are only ever likely to experience a slight lethargy.

best hemp oil for dogs
Canine Support Formula will help calm your pet, alleviate joint pain & balance brain neurotransmitters to reduce seizure activity in dogs.

How CBD Reduces Seizures & Protects Your Dog’s Nervous System

While there’s no cure for seizures, you can mediate the potential neurological damage by giving you dog a daily dose of premium, full spectrum CBD oil.

Seizures can be thought of as starting from neuro-inflammation in the brain. And 80% of neurotransmissions (neuron firing) can be attributed to the activity of two neurotransmitters – GABA & Glutamate.

GABA is primarily involved with rest, repair and general brain detoxification. Glutamate, on the other hand, is responsible for the ‘fight or flight’ response & anxiety behaviors.

Phenobarbital (and other barbiturates) work by decreasing the effect of the neurotransmitter glutamate in the brain–the same pharmacological mechanism that CBD does to effectively reduce seizure activity. 

CBD (Cannabidiol) from hemp both decreases and stabilizes the neuron activity in your pet’s brain, which can help reduce the number of seizures your pet experiences.

Like Pb, CBD also crosses the blood-brain-barrier to increase activity of the GABA neurotransmitter, which is what calms the nerves–and it decreases activity in the Glutamate neurotransmitter (which reduces nerve-stimulating properties). What CBD does is bring down the level of glutamate re-cycling in the brain so there is a more balanced level of both GABA and glutamate.

how to give cbd oil to dog
Oral sublingual CBD oil for control of seizures is the preferred delivery method for it’s higher absorption & bioavailability.

Essentially CBD brings about more balanced brain activity by regulating these two neurotransmitters resulting in less anxious behavior in your dog.

CBD is also an antioxidant and neuro-protectant that works by reducing the number of free-radicals produced in the brain that creates an over-excited neurotoxic state (again, too much glutamate) that results in fear, anxiety and stress responses (e.g., fight or flight).

So, using a CBD-rich hemp oil along with other antiepileptic (AE) medications can reduced the number and frequency of seizure episodes & diminished the impact in the aftermath of a seizure.

If you want to add cannabinoid therapy to support your dog with seizures, be sure to use a precise CBD dose based on your dog’s weight expressed in mgs per kg.

Remember, you and your dog have a lifetime with this disorder; but no matter what treatment option you choose (all-natural CBD vs traditional drugs OR a combination of both), you’re NOT treating a disease but only reducing the symptomatic effects of seizure activity.

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