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More on Epilepsy
What is Primary Epilepsy?
Primary or idiopathic epilepsy is the major cause of recurrent seizures in dogs between 1 and 5 years of age. Since no obvious evidence of brain injury is found in primary epilepsy, the probable cause of seizures may be related to a pre-existing or hereditary chemical or functional defect in the brain. The typical seizure due to primary epilepsy is a one to two minute generalized convulsion characterized by collapse, stiffening and/or paddling of the limbs, jaw-chomping, salivation, occasional loss of urine and/or feces, and unconsciousness (no response to calling, touching, etc.). Bear in mind, however, that primary epilepsy may be milder in nature and that not all of the above signs may be seen. A seizure event is typically followed by a "post-ictal" or post-seizure period characterized by incoordination, exhaustion, and disorientation. This period may last for minutes or hours and should not be confused with the actual seizure.
Diagnostic Work-up for Epilepsy
It is important to rule out other causes of seizures before concluding that a dog has primary epilepsy. Specific treatments are chosen based on whether your pet has primary epilepsy or secondary epilepsy (epilepsy due to another cause). For this reason, baseline laboratory tests are usually performed at the onset of epilepsy. It is also important to observe your pet in the periods between seizures (the interictal period) for evidence of neurological problems (change in behavior, circling, paw knuckling, etc.). Blood tests assessing liver and kidney function are also strongly advisable before starting an antiepileptic drug since the liver and kidney are responsible for breaking down and removing these drugs from the body. Brain imaging (CT or MRI) may be necessary if either neurological signs are present between seizures of if the seizures are responding poorly to antiepileptic drug therapy (both Phenobarbital and potassium bromide).
When to Start an Antiepileptic Drug and When to Recheck
We advise starting an antiepileptic drug if your pet has an average of 2 or more seizures per month, has one seizure that is very prolonged (more than 5 minutes), or has seizures which occur in a "cluster" (2 or more seizures in one 24 hour period). The goal of drug therapy is to decrease the number and severity of the seizures. A complete "cure" is rarely achieved. For optimal seizure control, close monitoring of seizure frequency and severity by you is essential. We recommend keeping a log of your dog's seizure events on a seizure calendar.
Of equal importance is a close monitoring of the blood levels of the antiepileptic drugs in your pet's bloodstream. The rate at which some dogs break down ("metabolize") antiepileptic drugs is more rapid than in other dogs, and this rate of breakdown may change over time. Consequently, a higher oral dose of the drug may be required in some dogs to achieve a "therapeutic" blood concentration. We will advise you exactly when to return for a "level check", but generally we perform level checks within 2 to 4 weeks of starting or changing the dose of a new drug, at 3 months, and then every 6 months thereafter.
Antiepileptic Drugs, Side Effects & Follow-up
Phenobarbital is usually the first line drug chosen for primary epilepsy. Common short-term side effects of phenobarbital are mild sedation and some incoordination. Longer term side effects may be increased appetite, and, occasionally, increased thirst and urination. After 7-10 days, these effects wear off and your pet should appear normal again. During this adjustment period, it is important not to lower the drug dose if these signs are seen. In about 2 weeks, a "steady state" or plateau level of drug in the bloodstream is reached, which is why we recommend a level check at this time. If the drug has reached a certain level in your pet's blood by 2 weeks that is considered "therapeutic", then we will not adjust the dose any further. If the blood level is too low or too high, then dose adjustments will be needed. After a therapeutic drug blood level has been attained, we recommend a recheck at 3 months, then every 6 months thereafter, or if seizure frequency exceeds more than 2 seizures per month. At recheck visits, a trough drug level is obtained to insure that therapeutic concentrations are still present.
We also obtain a blood test that assesses liver function since a rare, long-term side effect of phenobarbital therapy is liver toxicity. Drugs to be avoided, if possible, in a dog on phenobarbital are aspirin, tagamet (cimetidine), chloramphenicol (an antibiotic), and primidone and phenytoin (two other antiepileptic drugs).
If seizures are not adequately controlled by phenobarbital, we will probably add potassium bromide to your pet's antiepileptic medications. Potassium bromide and phenobarbital are very compatible with each other in controlling seizures and so are often used together. Occasionally, we will use potassium bromide by itself in first time epileptics. We formulate a solution of potassium bromide that can be mixed with food (if your pet eats all of its food) or added to a treat (a piece of bread, donut, etc.) that your pet will eat readily. It is important to avoid feeding salty treats or foods (hot dogs, "Snausages", "Beggin Strips", "Pupperoni", jerky treats, chicken broth, some prescription diets) if your pet is on potassium bromide. Excessive salt will lower the bromide concentration in the blood and prevent therapeutic drug levels from being attained. Since it takes a long period of time before plateau levels of bromide are reached, we recommend a level check at 1 and 3 months then every 6 months after starting potassium bromide. Short-term side effects to monitor for are sedation, incoordination, and, occasionally, increased appetite, increased thirst and increased urination. A long-term side effect of potassium bromide therapy in some dogs (usually occurring at very high drug blood levels) is rear limb weakness (difficulties getting up, climbing stairs, etc.). Call immediately if you see these signs and schedule a recheck appointment.
Newer anticonvulsant drugs:
While the majority of dogs respond very well to Phenobarbital and/or potassium bromide, there are a few dogs that will continue to have a high seizure frequency despite having adequate serum levels of these medications, and are called “refractory”. For these dogs newer anticonvulsants may help. Levetiracetam, gabapentin, and zonisamide are the medications most commonly used in cases of refractory epilepsy.
Per rectal diazepam:
Some epileptic dogs have a tendency to experience "cluster seizures" (2 or more seizures in a 24-hour period) even when being treated with Phenobarbital and potassium bromide. In these situations, the injectable form of diazepam administered rectally after the first seizure in the cluster has been shown to decrease the number and severity of subsequent seizures in the cluster. The dose is drawn up into a syringe with an adapter attached for easy administration rectally. The dose can be repeated up to 3 times in a 24-hour period. If seizures persist after the third dose, your pet should be seen by an emergency veterinary center.
Successful management of your pet's epilepsy requires close monitoring by both you and us. Careful and prompt drug level monitoring will provide long-term benefits in terms of seizure control and prevention of undesirable drug side effects. An acceptable quality of life for your pet and for you is our ultimate goal. We hope this overview will help you reach this goal.