Phenobarbital versus Potassium Bromide
Phenobarbital and potassium bromide (KBr) are the "go to" drugs to control seizures in pets. When I was in veterinary school, I was taught to first try phenobarbital, primarily because we had more experience with that drug. If phenobarb failed to provide adequate control of a patient’s seizures or was associated with unacceptable side effects (e.g., sedation, unsteadiness, increased appetite, thirst, and urination, or pronounced elevations in liver enzymes), then we should try KBr, either alone or in combination with the phenobarb, depending on the situation.
This is what I’ve done for the last 13 years or so, and the protocol works well in the majority of cases of idiopathic epilepsy. If it doesn’t, then I reach for some of the newer anti-seizure medications that veterinarians have borrowed from the world of human medicine.
Until recently, I couldn’t point to any research that supported my approach. That changed with the publication of "Comparison of phenobarbital with bromide as a first-choice antiepileptic drug for treatment of epilepsy in dogs" in the May 1 issue of the Journal of the American Veterinary Medical Association.
46 client-owned dogs that had been diagnosed with epilepsy (an abnormality in the brain’s electrical activity that causes chronic, recurrent seizures) but had essentially never been treated for the condition completed the study. 21 received phenobarbital and 25 KBr according to a dosing regimen that quickly brought the blood levels of the drugs into the low end of their therapeutic ranges. If an unacceptable level of seizure activity continued, doses were increased as appropriate to each dog’s situation.
The scientists followed the dogs closely for six months. They measured peak and trough levels of the drug in addition to a variety of other biochemical parameters one week after treatment began and monthly for the duration of the study. Owners also kept a calendar and log with daily entries regarding their dog's response to treatment, and referring veterinarians provided their assessments as well.
The paper concludes with the following statement:
This study demonstrates that both phenobarbital and bromide are reasonable first-choice AEDs [antiepileptic drugs], but phenobarbital may be more efficacious. Regarding adverse effects, phenobarbital may be more difficult to start if a loading dose is used; however, once steady-state serum concentrations are reached, adverse effects are more likely to persist for bromide. This study also suggests a poor relationship between drug dosage and serum drug concentrations, suggesting that serum drug concentrations should be monitored for guidance in adjustment of drug dosage as control is sought in epileptic dogs.
The take home message? Start with phenobarb unless KBr seems to be a better option based on a dog’s individual situation. Also, every dog reacts differently to these medications and those reactions can change over time. Patients should be monitored closely at the onset of treatment and then reevaluated every six months or so from then on.
I’m smiling … there’s nothing like a little confirmation that you’ve been on target all along to brighten your day.
Dr. Jennifer Coates