Dog Seizure Medication Side Effects

Dogs that are prescribed long term anti-epileptic drugs are at risk for a number of dog seizure medication side effects. Dogs are prescribed long term therapy when they have experienced cluster seizures, a status epilepticus, or two or more seizures within a six week period. Anti-epileptics, or anti-seizure medications, do not prevent all seizures but control them by minimizing occurrences and severity.

Dosage and concentration of anti-epileptic drugs is based upon a combination of effectiveness with the least side effects and toxicity. The primary concern in side effects of anti-eplileptics is hepatotoxicity, or toxicity to the liver, that can result in liver damage or failure. Medications that are prescribed for seizures in dogs include phenobarbital, potassium bromide, benzodiezapines, valporic acid, phenytoin and primidone.

It is important to note that with all seizure medications, abrupt discontinuation of the medication or a missed dose can result in immediate recurrence of severe seizures. This can also occur if dosage instructions are not strictly followed or if monitoring tests have not been maintained to determine the proper dosage and concentration.


Phenobarbital is a tablet form oral medication that is commonly prescribed to suppress epileptic seizures and has been shown to be highly effective. Possible side effects of phenobarbital include:

  • Excessive water consumption
  • Excessive urination
  • Increased appetite
  • Depression
  • Lethargy
  • Anemia
  • Hepatic toxicity

Phenobarbital is not recommended for dogs with liver disease. Long term administration can result in liver scarring, disease and failure. Phenobarbital blood level and liver function (bile acids) monitoring tests should be done every six months throughout administration of the medication. The effects of phenobarbital may be increased or decreased when it is administered with certain antibiotics or antihistamines. Phenobarbital may also reduce the effectiveness of other medication such as certain antibiotics, corticosteroids or heart medications.

Potassium Bromide

Potassium Bromide is a liquid solution or capsule form medication that restricts electrical activity in the central nervous system, inhibiting the onset of a seizure. Possible side effects of potassium bromide include:

  • Nausea
  • Excessive water consumption
  • Excessive urination
  • Drowsiness

Potassium bromide can intensify pancreatitis, especially if it is administered in conjunction with phenobarbitol. It is recommended for dogs with hepatic ailments because it is not metabolized by the liver.


Benzodiezapines are oral or injectable medicines that may be prescribed as seizure control medications for dogs that have been previously diagnosed with liver disease. Benzodiezapines have not been shown to cause liver damage and are generally well tolerated. The most commonly prescribed benzodiezapine for controlling seizures is diazepam. The side effect of primary concern for diazepam is drowsiness, but this is also considered a benefit as it is often prescribed for anxiety. Some brands of benzodiezapines have serious interactions with other medications such as:

Other Dog Seizure Medications

Primidone is an anti-seizure medication that is more expensive, less metabolically efficient and more damaging to the liver than phenobarbital, and therefore rarely prescribed.

Phenytoin is a slow release drug that may be prescribed as an anti-seizure medication. Phenytoin is severely damaging to the liver if administered in conjunction with other anti-epileptics, but as a sole medication it has approximately the same hepatotoxicity as phenobarbital.

Valporic acid has shown no indication of liver damage in dogs whether used alone or in conjunction with other medications, but is considered less effective at seizure control in some dogs.