What to Know About Phenobarbital for Dogs

Medically Reviewed by Vanesa Farmer, DVM on December 08, 2021
3 min read

Veterinarians use phenobarbital to treat dogs having seizures. The drug is categorized as a barbiturate. Phenobarbital is used to treat your dog if they have epilepsy or other seizures. This drug stabilizes the brain cells and prevents the unregulated electrical discharges in the brain that cause seizures.  

Seizures can cause brain damage if they go on for a long time, and your dog might be injured during one, so it's important to prevent seizures.

Seizures originate in the brain. Some common causes include:

  • Epilepsy
  • Encephalitis, an inflammation of the brain
  • Meningitis, an inflammation of the coverings of the brain
  • Brain cancer
  • Poisons
  • Liver or kidney disease
  • Low or high blood sugar or electrolytes
  • Head injury
  • Strokes

The most common cause of seizures is epilepsy, especially in young dogs. During an epileptic seizure, your dog may topple over, become stiff, or make jerky or paddling motions with their limbs. They are not aware of people around them and are unconscious for a while after a seizure. This condition may last from one to several minutes.

Any dog can have seizures, but some breeds are more likely to have them. Labrador Retrievers, German Shepherds, Beagles, and Border Collies have a higher likelihood of seizures.

Seizures can damage your dog's brain, especially if they are prolonged or very frequent. Your dog might also suffer a fall or 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 two or more seizures per month
  • Has prolonged seizures (lasting more than 5 minutes)
  • Has seizures that occur in a cluster (two or more seizures in one 24-hour period)

When used in dogs, phenobarbital often successfully controls seizures. Some dogs do not respond and need other drugs. Other anti-seizure medication for dogs include potassium bromide, levetiracetam, gabapentin, and zonisamide.  

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. Most anti-seizure drugs have a very short half-life, meaning they are quickly removed from the body by the liver or the kidneys. Such drugs need multiple doses a day. Phenobarbital offers the convenience of only requiring two doses a day.

This is not a drug you should use on your own. Always let your veterinarian prescribe a phenobarbital dosage for dogs.

The dose of phenobarbital has to be individualized based on blood tests. This is because your dog on phenobarbital may be metabolizing the drug faster or slower than normal. Blood level measurement helps veterinarians find the best dose for your dog. Such testing should be done:

  • Two to four weeks after starting phenobarbital
  • Two to four weeks after changing the dose
  • Three months after first starting treatment
  • Every 6 months while treatment is ongoing
  • Whenever seizure control is unsatisfactory

It is not possible to cure seizures with phenobarbital. Your veterinarian will aim to reduce the frequency and severity of seizures while keeping side effects at an acceptable level.

Being a drug that acts on the brain, phenobarbital has side effects involving the nervous system. Soon after starting, your dog may sleep more than usual. They may also be somewhat clumsy, tripping and bumping into doors and furniture. Your dog on phenobarbital may seem more thirsty and hungry than before.

These effects last a few days. Your dog will usually return to normal behavior in a week or two. It's important to not stop administering the drug or reduce the dose because of these side effects. Your veterinarian will adjust your dog's phenobarbital dose based on blood level testing and seizure control.

Some dogs on phenobarbital become hyperactive and aggressive. Other adverse effects include diarrhea, vomiting, poor appetite, and itching.

During prolonged use, phenobarbital in dogs can damage the liver. Your veterinarian will test liver function with blood tests at regular intervals to guard against this risk.

Phenobarbital treatment should not be stopped suddenly. The drug causes dependence, and abrupt stoppage can cause barbiturate withdrawal seizures. 

Seizures can cause injuries and brain damage, but anti-seizure medication for dogs can prevent or control seizures. Though many drugs are now available, phenobarbitone remains one of the most effective, safe, and convenient to use.