Why Phenobarbitol?

Potassium or sodium bromide (KBr or NaBr) have been very successful as second anti-epilepsy drugs (AEDs) since they were reintroduced about a decade ago. Many dogs with difficult seizure patterns have achieved better control with the combination of phenobarbitol and bromide. My Patrick never had another seizure after we added NaBr to his medication regimen. Today there are numerous dogs on bromide as sole therapy, either started that way or switched due to phenobarbitol-induced liver problems. This success has raised the obvious question "Why do vets prescribe phenobarbitol at all, if bromide is so successful?" (Information on bromide as an AED)


In 1994 when we were introduced to the world of canine epilepsy, very few general practice vets had even heard of using bromide as an AED. Phenobarbitol is a very effective AED, and that is the experience most vets had. Personally, I am delighted to see how quickly the knowledge of bromide's effectiveness as an additional drug has spread in the veterinary community. If they have been in practice for long at all, they have had to learn about it through continuing education. The vets still have less history with it, though, so it's no surprise that they first use the drug with the longer track record. Until the results from the Texas A&M study are published, you won't see many vets using bromide as sole therapy. The study may change that. Author's note: This study is complete, with results expected to be published before the end of 2001.

The "Average" Epileptic

If you are reading this article, you are probably not an "average" owner, and many of our dogs are also not "average" epileptics. The majority of dogs with seizures either do not require medication, or they are acceptably controlled on the first AED used. If their vets are sufficiently competent to do regular testing of blood levels and liver enzymes, they can live perfectly normal lives.

Time to Steady State

Phenobarb only takes 2 to 3 weeks to reach steady state, versus 3 to 4 months for bromide. A loading dose speeds that up, but is not without dangers.

Diet Considerations

Bromide and chloride compete for absorption in the body. Therefore, if the chloride content of a dog's diet changes, his bromide blood level will also change. That means that you have to be careful changing foods with a dog on bromide. If possible, it is best to switch to a food with a similar chloride content. Since that figure is not generally printed on the bag, a call to the manufacturer is necessary. With any diet (or water) change, you should recheck levels in a couple of months.

Owner Understanding

Most people can read the label on a bottle of pills and figure out that if they are giving one 60 mg. pill, their dog is taking 60 mg. of the drug. For someone who doesn't play with numbers for a living, it can be harder to translate that 2 cc of a liquid compounded at 250 mg./ml. is 500 mg. of the drug. That lack of understanding can make dosage adjustments more difficult.

Ease of Acquisition and Administration

Any pharmacy and most veterinary offices can dispense phenobarb, while you usually need to find a compounding pharmacy to fill a bromide prescription. Additionally, most pet owners already know how to give a pill, while few have experience dosing with a liquid. Remember that the vet is thinking about that "average" owner, who may not keep to a regular schedule if it is too much perceived trouble.

Drug Interaction

Many difficult-to-control dogs do better on the combination of phenobarb and bromide than on either one alone. However, the combination is more difficult to manage. Frequently people (or their vets) blame the second drug added without testing. In Patrick's case, addition of NaBr caused his phenobarb level to increase. We were able to lower that dose and get good control without ataxia.

FDA Approval

I have heard speculation that the reason vets don't prescribe bromide first is because it is not approved by the Food and Drug Administration. In fact, neither phenobarbitol nor bromide is specifically FDA approved. Most human drugs used in veterinary medicine are not explicitly approved for use in dogs. The approval process is expensive, and most drug companies would not spend extra money to gain the approval. Therefore, it is absolutely critical that pet owners fight any legislation that would ban the extra-label use of "human" medications by veterinarians.

updated 6/30/01

Deb R.

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