What is epilepsy?

Epilepsy is an abnormal discharge of nerve cells within the brain that causes complete or partial loss of brain and body function. Often these "seizures" take the form of a grand mal convulsion during which the pet may completely lose conscoiusness and control of all bodily functions.

What causes epilepsy?

Epilepsy usually begins because an “irritable focus” of nervous tissue in the brain begins to discharge spontaneously. If this electrical discharge spreads to adjacent cells an uncontrolled discharge of neurons may spread throughout the brain and cause a convulsion. There are many potential causes of a seizure focus such as a brain tumor, infection, or poisoning. If an animal does not have an identifiable cause of the seizure, it is called “idiopathic” epilepsy. Idiopathic epilepsy is caused by a congenitally acquired tendency to have an overactive seizure focus.

 

How is idiopathic epilepsy treated?

 

If a seizure episode occurs only occasionally (less than once every 2-3 months) and is relatively mild, it may not be necessary to treat with anticonvulsants. If, however, the seizure episode lasts over 2-3 minutes or if several seizures occur in succession, such as 3-4 per day, it may be necessary to treat with anticonvulsant medication even though the “clusters” are infrequent.

 

The anticonvulsants of choice most commonly used in the dog are phenobarbital and potassium bromide. Most of the other anticonvulsants used to treat humans with epilepsy are either too rapidly metabolized in the dog or cause signs of toxicity, especially liver toxicity.The incidence of liver toxicity due to phenobarbital is approximately 11%.

 

What are the side effects of phenobarbital and/or bromide?

 

Phenobarbital, especially when first instituted, can cause signs of drowsiness or sometimes hyperactivity, wobbly gait, increased thirst, or increased appetite. These signs are not seen in all cases and when seen during the first few days of treatment are not cause for alarm. These signs usually disappear within 10-14 days. However, if the signs persist or are particularly distressing to you or your pet notify your veterinarian.

 

Bromide when used as the sole anticonvulsant appears to be relatively free of side effects as long as blood levels are within the therapeutic range. At high doses, it can cause sedation, especially when used in conjunction with phenobarbital. It can cause vomiting in some dogs due to gastric irritation. This is usually overcome by giving medication immediately after a meal.

 

How do we determine the correct dosage of anticonvulsant medication?

 

In order to be effective in suppressing seizure activity the dosage of anticonvulsant must be tailored for each animal. Individual dogs may metabolize drugs at different rates resulting in different concentrations in their bloodstream and brain tissue. When anticonvulsant medication is first instituted the dose is a “calculated guess”. However, after a period of 10-14 days in the case of phenobarbital and 6-8 weeks in the case of bromide, the concentration in body tissues begins to level out. After that period a blood sample should be taken and the anticonvulsant concentration measured. The concentration of phenobarbital should be between 25 and 40 mcg/ml and that of bromide between 100-200 mg/dl. If outside this range, an adjustment will be made. Usually it is necessary to make 2 or 3 such measurements at several week intervals in order to fine tune the drug dosage.

 

Phenobarbital: check blood levels at 2 weeks, 2-1/2 months, then every 6 months thereafter.

 

Bromide: check at 8 weeks, 6 months then annually.

 

As with most long-term treatment regimens, red and white blood cell counts and serum chemistries should be checked annually to make certain there are no toxic side effects from the medication.

 

Is the time of day important when a blood sample is taken for anticonvulsant drug measurement?

 

Yes. When measuring anticonvulsant levels, particularly phenobarbital, it is best that the sample be taken when the drug is at its lowest level which occurs just prior to receiving the next dosage. For instance, if a dog is receiving phenobarbital on a twice daily basis (every 12 hours) a blood sample should be taken between 10 and 12 hours after the last dose. If seizures are not adequately controlled it may be necessary to check anticonvulsant levels more frequently and increase the dosage until the level is at the high end of the therapeutic range.

 

Can medication keep my pet seizure free?

 

The goal is to eliminate seizure activity but that is not always possible. We sometimes cannot eliminate seizure activity completely but usually can reduce the severity and frequency to an acceptable level. Keep in mind that if your pet has idiopathic epilepsy periodic seizures may be unavoidable. If these seizures are of short duration and occur only occasionally a change in medication may not be necessary. If seizures are not controlled adequately with one anticonvulsant alone then an additional anticonvulsant medication may be added. People often ask about diphenylhydantoin (Dilantin®), valproate (Depakene®), carbamazepine (Tegretol®) and other anticonvulsants commonly used in humans with epilepsy. These medications are occasionally used in dogs but because of the dogs’ metabolism it is difficult to achieve therapeutic levels. These drugs are generally not effective and are toxic to the liver at the levels needed to control seizures in dogs. Some newer drugs that appear to have some benefit when used in conjunction with phenobarbital and bromide.

Back to contents

Visit our Links to Other Sites