Medications used for the control of seizures and certain compulsive behaviors have evolved over the years. While the doctors at the Animal Clinic at Thorndale most often use phenobarbital as the first line of treatment, we now have other medications we can add on or transition to if the phenobarbital alone is not giving good control. Sometimes other medical problems, such as liver disease, dictate selecting a different class of drugs. Fortunately, most dogs do very well on phenobarbital alone. It is readily available by prescription at most human pharmacies and remains relatively inexpensive. This is an important consideration when looking at a lifelong of treatment for some disorders.
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 usually the first medication selected for seizure control.
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 will be increased. If excessive drowsiness or staggering occurs, the dose will be adjusted. Please note that this drug should be given twice daily (every 12 hours) 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:
- 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. It is normal for a dog just beginning treatment to be somewhat sedate.
- 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 after 7-10 days. If that change causes drowsiness, another adjustment may be needed.
Phenobarbital is a barbiturate and as such is addictive. Do not stop the drug without direction from your veterinarian. Usually the dose will need to be tapered down over time if the medication is to be stopped. Even when abruptly stopping this drug in healthy dogs, seizures can be induced. Dogs also may develop a tolerance over time. It is very likely that the dose to control seizures will need to be increased over the dog’s lifetime. It is very important that blood levels of phenobarbital and other liver parameters be monitored as directed by your veterinarian. There is a “therapeutic window” of blood levels of phenobarbital in which the dose is considered safe, with minimal side effects. If the blood levels are above this window to achieve control or safe control of seizures cannot be maintained inside this blood level range, other medication will be added on or substituted to provide better control and safety. If you are uncomfortable concerning your dog’s response to phenobarbital, do not hesitate to call for assistance.
The goal of anti-convulsant therapy is to reduce the frequency and severity of seizures. Be aware that seizures are generally not totally eliminated and status epilepticus can still occur in an apparently well controlled dog. Click here to read more about seizures.