Stan Wood, DVM, Diplomate ABVP

Specialist in Canine & Feline Practice

Use of Phenobarbital in Dogs

Phenobarbital is a very safe and effective drug that has been used for many years in dogs. It is principally used for seizures.

Phenobarbital is a depressant of the central nervous system (brain and spinal cord). If it is overdosed or if your dog is especially sensitive to it, drowsiness, excessive sleep, and even staggering when walking will occur. On the other hand, if it is not dosed high enough the desired effect will not be achieved. Therefore, our goal is to find the dose that controls the problem without causing drowsiness and staggering.

Some dogs are more sensitive to this drug than others; therefore, the initial dose is always subject to change. If no response occurs, the dose should be doubled. If excessive drowsiness or staggering occurs, the dose should be cut in half. However, please note that this drug should be given twice daily for best results. Since some of the tablets are so small it is tempting to lower the initial dose to once daily. However, to get best results the lower dose should be given twice daily.

Phenobarbital is metabolized (broken down) by the liver so it can be eliminated from the body. However, dogs do not have a very efficient system for doing this at first. But when the dog has been taking it for about 7-10 days the liver creates new enzymes that make this elimination process more efficient. This means that the dog will effectively lower its own dose after 7-10 days because the drug will be broken down and eliminated more rapidly. This has some important implications in treatment:

1. If your dog is initially slightly drowsy, sleeps slightly more than normal, but does not stagger when walking, continue that dose. After the 7-10 days initial period, these signs of overdosing will go away as the liver works more efficiently.

2. If your dog has a very good response but is not drowsy during the first week of treatment, it is possible that the response will diminish when the liver becomes more efficient at metabolism. This means that you may need to increase the dose (usually double it) after 7-10 days. If that change causes drowsiness, try a dose midway between the low one and the high one.

If you are uncomfortable concerning your dog's response to phenobarbital, do not hesitate to call for assistance.