Selecting First-Choice Anti-Seizure Medications for Dogs

02/15/2013

Epilepsy is a medical condition found in both dogs and humans. The seizures it causes can be quite dangerous, and although it is often treatable, there has been some debate over which anti-epileptic drug (AED) is most effective. In part, this is because the ability of any given drug to control seizures has to be balanced with the risk that it may cause unacceptable side effects. Unfortunately, few studies have directly compared the efficacy and safety of the major anti-epileptic drugs in dogs.

That’s why, in a study supported by the AKC Canine Health Foundation, Dr. Dawn Merton Boothe and her colleagues set out to determine whether phenobarbital or bromide treatment is the best initial treatment choice in epileptic dogs. They are the two drugs most commonly used to treat canine epilepsy, but doctors often have a difficult time choosing between them, as each has its benefits and disadvantages. For example, the side effects of phenobarbital are potentially more severe than those from bromide, but this might be offset by the fact that phenobarbital is cleared more quickly from a dog’s system. When a dog has adverse side effects on phenobarbital, the drug can be stopped, and symptoms usually improve within days. In contrast, bromides are less likely to cause side effects, but any that appear can continue to affect a dog for several months after the medication is discontinued.

Dr. Boothe’s research weighed the relative advantages and disadvantages of the two drugs and showed that both were reasonable choices for epilepsy treatment. However, phenobarbital seemed slightly better overall, despite the risk for potentially more serious side effects. This was primarily because a significantly larger percentage of the dogs receiving phenobarbital had seizures that were fully controlled by their medication, and because the breakthrough seizures that occurred on that drug were shorter in duration than those dogs had while being treated with bromide. In addition, seizures actually got worse in three of the dogs treated with bromide, something that wasn’t seen in any of the dogs on phenobarbital.

That said, early on in the study, side effects were slightly worse for those dogs treated with phenobarbital. One month into treatment, those dogs were more likely to be lethargic, excessively thirsty, and have trouble controlling their body movements than dogs on bromide treatment. However, these symptoms significantly improved with time. After six months of treatment, dogs that were treated with phenobarbital had no more side effects than those treated with bromide. In contrast, dogs treated with bromide had problems with vomiting and lethargy throughout the study period, and they were more likely to discontinue treatment because of adverse events. Therefore, although the side effects seen in the early days of phenobarbital treatment can be discouraging, it may be worth pressing on. Most dogs will do much better with time.

Taken as a whole, the combination of increased efficacy and fewer long-term, problematic side effects led the scientists to conclude that phenobarbital was a slightly better choice than bromide for the treatment of epilepsy in dogs; however, they warned that their results need to be treated with caution. Two of the most important things they discovered were how variable phenobarbital levels were in treated dogs, and the extent to which dogs’ metabolism of the drug could change over time. Therefore, the other critical take home message from their research is that it’s extremely important for veterinarians who are treating dogs with epilepsy to continually monitor the amount of drug present in a dog’s blood. The dose needed to maintain therapeutic levels can change substantially over the course of even six months of treatment, and many dogs will need to be treated for years. Only with regular monitoring can doctors be certain that dogs are getting enough phenobarbital to control seizures while still keeping the dose low enough to avoid unnecessary side effects.

This work was funded by AKC Canine Health Foundation Grant 1280.

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