Phenobarbital is a barbiturate used to prevent seizures or control status epilepticus (seizures lasting for 30 minutes or more). Because it is relatively cheap and is effective for the majority of dogs, it’s a common choice of medicine. It is also used less commonly for its sedative properties.

Phenobarbital vs. potassium bromide: When it comes to treating pets with seizures, the other go-to medicine is bromide. Bromide is a good choice for young dogs or dogs with impaired liver function, but we recommend phenobarbital whenever possible because it tends to be more effective. You can also use the two medicines together if either one on its own does not work well enough.

What’s The Dosage?

Note: Never give this medicine to your dog without consulting your vet first.

The usual dosage of phenobarbital to treat seizures in dogs is around 1 – 1.8 mg/lb every 12 hours, but it depends on how bad the seizures are. If seizures are severe, a “loading dose” may be required where a larger amount of around 9 mg/lb is injected intravenously (at a maximum rate of 60 mg per minute). The vet will monitor your dog every few weeks or months by taking blood tests and judging how effective the medication has been in the prevention of seizures. They may decide to adjust the dosage based on their findings until everything is stable, at which point you may only need to return once yearly for a check-up.

A dosage of 1 mg/lb is shown on the chart below.

Chart of the phenobarbital dosage for dogs

In puppies your vet will probably choose a dosage 50% to 100% higher than our recommendation to compensate for their fast metabolism. Administering the medicine at the same times each day is recommended.

Diazepam should be attempted first for cases of status epilepticus, but if this fails, phenobarbital can be given at a dosage of 0.91 – 2.2 mg/lb, and then again every 20 minutes up to two times.

For alternative uses…

When used for sedation 1 – 3 mg/lb can be administered twice daily, or up to 9 mg/lb twice daily for compulsive behaviors. In both of these cases it should be taken by mouth.

Example: A 20 lb dog could be started on 20 mg every 12 hours. If a “loading dose” is used, an IV injection of 180 mg could be administered by the vet.

Is It Safe?

Phenobarbital is quite safe for healthy dogs but can put some strain on the liver, making it unsuitable for those with poor liver function unless protective drugs are given in conjunction. Use cautiously when treating those with the following conditions:

  • Adrenal insufficiency
  • Anemia
  • Heart or respiratory disease
  • Hypovolemia

The injectable form should be administered slowly to avoid respiratory depression, and should never be injected perivascularly or subcutaneously.

Pregnancy: This medicine can be damaging during pregnancy and should not be used in these cases unless completely necessary.

Usage Guidelines

The following guidelines will help you safely treat your dog with phenobarbital:

  • Only begin treatment under the guidance and approval of a vet
  • Tell the vet about any medical conditions your dog has, or any other medicines/supplements you are giving him
  • Avoid injecting subcutaneously or perivascularly
  • The medicine should not be injected at a rate of more than 60 mg per minute
  • Administer the drug at roughly the same time every day to keep levels stable
  • When used long-term, regularly blood testing (often every 6 months) is advised
  • Contact the vet if treatment does not reduce seizure activity

A large number of drugs interact with phenobarbital, so always tell your vet about any other medicines (or even supplements) your dog is taking. Some of the more common medicines which interact with phenobarbital includes antihistamines, MAOIs, corticosteroids and antibiotics such as doxycycline and metronidazole.

It’s also important to mention that unless food and water intake is monitored, the increased appetite, thirst and urination could lead to a false Cushing’s disease diagnosis.

What Is It Used For?

This medicine is usually used to treat the following conditions:

  • Compulsive behaviors
  • Seizures

It is also sometimes used as a sedative, or in rare cases, for the treatment of compulsive behaviors.

Side Effects

The drug is often well tolerated. However, during treatment the following adverse effects could occur:

  • Anxiety
  • Increased frequency of urination
  • Increased hunger
  • Increased thirst
  • Lethargy
  • Loss of coordination


  • Anemia
  • Liver damage
  • Reduced neutrophil count
  • Reduced platelet count
  • Superficial necrolytic dermatitis (SND)

Increased thirst, increased appetite, increased urination, sedation and loss of coordination become common when blood serum levels of the drug are high. Symptoms of anxiety and lethargy tend to pass with time, but tell your vet if they do not.

In rare cases serious liver disease can occur, especially when multiple anti-seizure medicines are being used at the same time. If you notice signs of liver problems (jaundice, abdominal swelling, loss of appetite) contact the vet immediately. You should also call the vet right away if you notice symptoms of anemia such as fatigue and pale gums.


Dr. R LeCouteur
Dr. T Axlund
Plumb’s Veterinary Drug Handbook (sixth edition)