By Jay McDonnell, DVM, MS, Diplomate ACVIM (Neurology)
Seizures are one of the most common complaints in veterinary neurology. While canine seizures may be caused by head trauma, brain tumors, toxins, infections, birth defects and many other identifiable causes, the vast majority of seizures in young dogs (one to three years old) are idiopathic or genetic epilepsy.
By definition, an idiopathic epileptic
- has their first seizures between one and four years old.
- has a normal metabolic workup, including a chemistry profile, pre- and postprandial bile acids, CBC and urinalysis.
- has a normal interictal neurologic exam.
- if performed, the brain MRI and CSF analysis are normal.
The type and frequency of seizures—partial/focal, generalized, cluster, etc.—does not necessarily reflect the underlying cause. For example, patients with idiopathic epilepsy can initially present with cluster seizures or even in status epilepticus. Alternatively, a patient with a brain tumor may present having had a single generalized seizure, after which their recovery is complete and their neurologic exam is normal.
Fortunately, good management of canine idiopathic epilepsy is possible in about 70 to 80 percent of cases treated with either phenobarbital (PB) or potassium bromide (KBr) monotherapy. Unfortunately, there are very few hard and fast rules when it comes to managing seizures in dogs (and cats, for that matter). Every case is unique and the decision as to which anticonvulsant(s) to use should be based on:
- Age of the animal (i.e., KBr may be a better first choice in a very young animal with infrequent seizures).
- Seizure frequency.
- Owner compliance/ease and frequency of administration.
- Side effects.
- Cost of medication and therapeutic monitoring (i.e., serum drug concentrations, chemistry, CBC, etc.).
General guidelines for when to start an anticonvulsant include:
- More than one grand mal tonic clonic seizure every six to eight weeks.
- More than one seizure in a 24-hour period (i.e., cluster seizures).
- Status epilepticus (seizure activity lasting longer than five minutes; two or more seizures without complete recovery between them).
PB and KBr are great first-line anticonvulsants.
- PB is probably a better choice for patients with frequent seizures or those who present with cluster seizures or in status epilepticus.
- On the other hand, KBr may be the best choice for a patient with underlying liver dysfunction.
- In some situations, we may start PB and KBr concurrently and once the seizure control is deemed adequate, we may wean the patient off PB.
The side effect profile is about the same for these two drugs. Patients are going to eat more, drink more, urinate more and may be quite sedate and incoordinated with initiation of the medication. Gastrointestinal upset is also possible with KBr. Fortunately, the sedation and incoordination tend to be transient, with most patients acclimating about two weeks into treatment. Unfortunately, the other side effects remain and are generally dose-dependent.
Other general guidelines: The starting dose for PB is 2-3mg/kg PO q. 12 hours.
- We recommend checking serum PB concentrations 10 to 14 days after initiating treatment or after any dose adjustment.
- Every six to twelve months, check a PB serum concentration and serum chemistry.
- PB may induce ALP production by the liver, which can be marked in some patients.
- If you become concerned regarding hepatic dysfunction, check pre- and postprandial bile acids with other blood work.
- PB will cause the liver to enhance its own metabolism with chronic administration, so dose increases may need to be performed over time.
If your first choice is KBr, we recommend loading a patient on this medication; otherwise it can take up to two to three months to reach therapeutic concentrations. There are two loading schemes that can be tailored to the individual situation:
- If the dog is having frequent severe seizures, load at 100-150mg/kg PO q. 6 hours x 4 doses (which equals 400-600mg/kg total dose given in a 24-hour period). The drawback to this scheme is that the dog can become overly sedate for two to three days or longer.
- If the dog has an interictal period of more than 7 to 10 days, load by giving 40 mg/kg twice a day for 10 days.
- Maintenance dose of 30-40mg/kg PO q. 24 hours.
- KBr must always be given with food, as it can cause GI upset (vomiting) when given on an empty stomach.
Considerations for cats: Cats are special in so many ways, but especially in regards to seizures. Some neurologists do not recognize feline idiopathic epilepsy as a disease entity. We do “see” this as a disease, but recognize that it is more common for cats to have underlying disease.
- For that reason, we feel it is very important to fully work up feline seizures, no matter the age.
- In regards to anticonvulsants, we recommend PB as our drug of first choice. In general, cats tolerate PB very well. Start at 2 mg/kg BID.
- Do not use KBr or diazepam as both of these drugs can cause severe complications unique to cats.
The goal of seizure management is three-fold:
- ‘Control’ of seizures, i.e., reducing the seizure frequency and severity.
- Imperceptible—or at least acceptable—side effects.
- Low cost for drugs and monitoring.
Rarely are we successful in achieving all three goals. We typically compromise to reach a majority of these goals. This is an important fact to review with owners so that their expectations are reasonable. If you have a question about a patient with seizures or anticonvulsant recommendations, please feel free to call us.