Written By Grace Park
Published: 12/11/2020Updated: 12/16/2020
Phenobarbital | Wag!

Phenobarbital for dogs is most often used to treat seizure disorders such as those caused by poisoning, brain tumors, infectious diseases, and epilepsy. Phenobarbital administered at home is to help control seizures.

It is important to note that this drug is prescribed with great consideration only. Phenobarbital is given with the following criteria:

  • Seizures are more than once a month
  • Cluster seizures have occurred
  • Seizures last more than 5 minutes
  • Seizures or after-effects are severe

Phenobarbital is in the drug class known as barbiturate anticonvulsant/hypnotics. This medication must be closely monitored by the veterinarian. Continue reading for information on dosage, efficacy, side effects, and considerations for phenobarbital.


The use of phenobarbital is described as antiepileptic drug therapy. This medication is often given twice a day. The dosage is determined by the veterinarian based on the specific seizure disorder and the frequency of the seizures. Phenobarbital is prescribed per weight, but it is not a drug to be administered to your pet without the continual care of the veterinarian.

Phenobarbital can be given in thefollowing forms:

  • Capsule
  • Tablet
  • Paste
  • Liquid
  • Chewable pill
  • Injection (in a hospital setting)

Dosage Instructions

Although this drug is given with or without food, if a dog experiences vomiting when administered on an empty stomach, it is recommended that it be taken with food moving forward. 

Phenobarbital cannot be stopped without a veterinarian’s instructions. Physical dependence can occur, and stopping abruptly can cause withdrawal seizures. The level of medication your dog is receiving will be monitored and possibly adjusted two weeks after the medication is first started, two weeks after any change in dosage, and every six to twelve months after the successful control of seizures at a specific dose.


After several doses, improvement is often noted. It may take a few weeks before significant effects are seen. If you miss a dose, you can give it when you remember, but not if it is close to the time of the next dose. Never give extra doses, or two at once.

A long-term study determined that dogs with epilepsy responded well to treatment when the medication was prescribed early on in the disease process. Although the study was done involving Labrador Retrievers, it is known that Australian Shepherds and Border Collies are more apt to have severe clinically reported episodes (especially Australian Shepherds). Other breeds noted to sometimes have epilepsy are:
  • Beagle
  • Belgian Tervuren
  • Burmese Mountain Dog
  • Dalmatian
  • English Springer Spaniel
  • German Shepherd
  • Irish Wolfhound
  • Keeshond
  • Lagotto Romagnolo
  • Shetland Sheepdog
  • Standard Poodle

Side Effects of Phenobarbital

There are side effects of phenobarbital for dogs, which should be monitored. When the medication is first started, there may be signs of depression and sedation. This is usually temporary and will resolve as the body gets used to the drug. After a 2 week trial, the medication amount may be altered.

  • Sedation and lethargy
  • Excessive appetite
  • Excessive thirst
  • Excessive urination
  • Restlessness
  • Hyperexcitability

Less common side effects are sometimes seen.

  • Liver toxicity which may present as yellowing of the skin, vomiting, skin ulcers
  • High enzymes on blood work
  • Loss of muscle control
  • Incoordination
  • Anemia


As with any medication, let your veterinarian know if your dog is taking holistic therapy, supplements, or vitamins. 

Drug interactions

Many drugs can possibly interact with phenobarbital for dogs. Your vet will discuss the importance of taking precautions.

  • Acetaminophen
  • Benzodiazepines
  • Carprofen
  • Monoamine oxidase inhibitors
  • Opioids
  • Phenytoin
  • Rifampin

An increase in the effects of phenobarbital may be seen with the following:

  • Antihistamines
  • Bromides
  • Chloramphenicol
  • Felbamate
  • Fluconazole
  • Opioids
  • Phenothiazines
  • Urinary acidifiers
  • Valproic acid

There is also a very long list of other medications that may contraindicate by decreasing the effect of phenobarbital for dogs. Your vet will have a detailed list to include some antibiotics, anticoagulants, dexamethasone, prednisone, warfarin, and zonisamide.

Allergic reactions and sensitivity

Although allergic reactions may be rare, if you have any concerns about symptoms or behavior in your pet, contact the veterinarian immediately.

Dogs with liver disease or poor liver function may not be prescribed phenobarbital. Phenobarbital for dogs can interfere with tests for Cushing’s disease and thyroid function. Dogs will need to be weaned off the drug. Do not stop it without tapering instructions from the veterinarian because severe seizures may result.

Frequently asked questions

What kind of monitoring will the veterinarian do if my dog is taking phenobarbital?

Dogs taking phenobarbital will be regularly monitored with blood tests two weeks after the medication is first started, and two weeks after a dose is changed. Sometimes it takes a bit of adjusting to get the best dose. Moving forward, your dog will be seen at the veterinary clinic every 6-12 months once control of the seizures has been achieved.

What should I do if I think there is an adverse reaction or an overdose?

Contact the veterinarian right away. If you cannot reach them, contact the emergency clinic.

How do I store the drug?

Phenobarbital should be stored in a cool, dry place away from light. Keep out of the reach of children and pets.

Do I need a prescription for phenobarbital?

Yes, a prescription is required. The use of this drug will be closely monitored by the veterinarian.

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© 2023 Wag Labs, Inc. All rights reserved.