Brain Disease in Dogs: Treating Seizure Disorders with Phenobarbital and Potassium Bromide

Treatment of seizure disease in dogs has changed over the past decade with the introduction ofBrain Disease in Dogs: Treating Seizure Disorders with Phenobarbital and Potassium Bromide several new anticonvulsant drugs.  However, phenobarbital and potassium bromide continue to be the first-choice anticonvulsant drugs to treat seizure disease in dogs.  Phenobarbital and potassium bromide tend to be very effective at controlling seizures in dogs and have the advantages of being inexpensive and drugs that most veterinarians are familiar with.

Phenobarbital as an anticonvulsant used to treat seizure disease in dogs.

Phenobarbital is the most commonly prescribed anticonvulsant used to treat seizure disease in dogs.  Its ability to control seizures in dogs has been well documented.  It is a relatively inexpensive, well-tolerated drug in dogs that can be administered two to three times a day.  The drug can be administered either intravenously or orally.  It does have a sedative effect in dogs, but over time, dogs tend to adapt to the effects of the drug and become less sedate.  Increased water intake and urination along with increased appetite are possible side effects.  Increased liver enzymes are commonly observed, but not necessarily indicative of liver dysfunction, which is more likely to occur with higher doses of the drug.  The drug can alter thyroid tests and result in a misdiagnosis of hypothyroidism.

Potassium bromide as an anticonvulsant used to treat seizure disease in dogs.

Potassium bromide therapy is thought to control seizure disease in dogs, but is less proven than phenobarbital in controlling seizures.  It is given orally in either a liquid or capsule form.  Bromide ions compete with chloride ions across the cell membranes, resulting in membrane hyperpolarization, thereby raising the seizure threshold and limiting the spread of epileptic discharges.  One concern is that it may take upwards of 4 months to reach a steady state concentration in the brain and that dogs could be unprotected during this time period.  This is due to the very long serum half-life of the drug in dogs.  This is sometimes overcome by the administration of higher doses of the drug initially, called a loading dose.  This long serum half-life allows for more flexible dosing of once a day.  It is a salt solution, which can sometimes be upsetting to the intestinal tract of dogs, resulting in vomiting or lack of appetite, so it is best given with food.  It does cause transient sedation in dogs, lasting up to 3 weeks, especially in dogs receiving phenobarbital concurrently.  Additional side effects include increased water intake and urination, and constipation.

Treatment of seizure disease in dogs when phenobarbital or potassium bromide is not successful as single drug therapy.

Anticonvulsant drug therapy to treat seizure disease in dogs should be changed when either no improvement in seizure control is observed despite maximal tolerated dosages of the drug or when toxic effects of the drug develop.  Phenobarbital is potentially toxic to the liver and the risk increases with higher doses of the drug.  Often times, potassium bromide may be used together with phenobarbital to control seizures that are resistant to single agent therapy.  Not every epileptic dog can be managed successfully with the common anticonvulsant drugs.  There are several new anticonvulsant drugs that are available and may be new protocols that have been recently introduced to help control seizures in dogs.  A veterinary neurologist who specializes in treatment of seizure disease in dogs may be able to provide important insights to help accomplish the common goal of improving the quality of life of a dog with seizure disorder.

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Dr Stephen Atwater

Stephen W. Atwater, DVM, MS, Diplomate ACVIM (oncology) is a board-certified veterinary oncology specialist. His professional interests include utilizing emerging therapies for difficult to treat cancers.

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