Seizures are a common complaint in veterinary medicine. 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 (1-3 year old) dogs is idiopathic or genetic epilepsy. Good management of canine epilepsy is possible in about 70-80% of cases treated with either Phenobarbital (PB) or potassium bromide (KBr) monotherapy. Treatment success is defined by reduction of seizure severity or seizure frequency with few side-effects. A rough treatment goal is a short (30-60 second) seizure every 6-8 weeks although each case is unique. Successful therapy is guided by excellent adherence to scheduled administration of anticonvulsants, a seizure log, regular veterinary examination and monitoring serum anticonvulsant concentration. A seizure log should include the following info: when seizures occur, how long they last, the post-ictal recovery and any possible precipitating events.
Monitoring serum anticonvulsants is an important part of caring for epileptics. Serum concentrations for PB and KBr are published and can vary with laboratories. Serum separator tubes should not be used for PB concentrations because the silicone binds the drug, resulting in artificially low measurements. Serum PB concentrations should be taken at the trough right before the next dose is due if seizure control is less than ideal. Serum KBr concentrations are less sensitive to when taken through the day. For monotherapy, management is less than ideal if the seizures continue to be severe or frequent and PB concentration is greater than 30 mg/dl or KBr concentration is greater than 2.0 mg/ml. The attached algorithms will assist you in treating the difficult to control epileptic.
Of the 20-30% of poorly controlled epileptics, more than half can be helped with polytherapy by combining either KBr or PB. By instituting polytherapy, lower total doses of PB can be used and up to 95% of epileptic dogs can be controlled.
Precautions and warnings to owners treating epileptics with anticonvulsants:
Phenobarbital:
· This medication is a long-acting barbiturate capable of suppressing seizure activity in the brain.
· Phenobarbital is a very safe and effective drug that has been used for many years in dogs. It is an inexpensive drug though the monitoring necessary amounts to about $300 per year.
· It takes 1 to 2 weeks to build up a blood level capable of suppressing seizures. This means that the effectiveness of a given dose cannot be assessed before this period. After this time, a phenobarbital blood level should be run to determine the effectiveness of the dose being used. Phenobarbital blood levels, once therapeutic, are checked every 6 months or sooner if breakthrough seizures occur.
· 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 will go away as liver metabolism adjusts.
· It is essential that you give phenobarbital as prescribed. Give it as close to the prescribed times as possible - if it is prescribed twice a day - it should be given every 12 hours. If you feel your pet is having a bad reaction to the drug, please call us up rather than just stopping the phenobarbital.
· Another important part of monitoring regards the toxicity of phenobarbital. This medication can be harmful to the liver thus liver function is periodically checked. It is important to report to your veterinarian any dramatic change in your pet’s appetite, weight or increased sedation.
Potassium bromide:
· Potassium bromide (bromide) is a salt that can be administered by mouth. It is believed to suppress seizure activity in the brain through hyperpolerizing the neuronal membrane. It is an inexpensive drug though the monitoring necessary amounts to about $4-500 per year for a 30 lb dog.
· It takes about one month to build up a serum concentration capable of suppressing seizures and up to 3 months before steady state values are approximated. This means that the effectiveness of a given dose cannot be assessed before this period. After this time, a potassium bromide serum concentration should be run to determine the effectiveness of the dose being used.
· If your dog is initially slightly drowsy, sleeps slightly more than normal, but does not stagger when walking, continue that dose. After 4-6 weeks, these signs will go away.
· Bromide can be given as a solution or a compounded capsule. The solution is typically less expensive and easier to adjust dosages.
· To reduce the stomach upset that can be seen with this medication, give with food.
COMMON SIDE EFFECTS FOR PHENOBARBITAL and POTASSIUM BROMIDE
SEDATION - animals may become quite stuporous as they get used to this drug. This effect is temporary, lasting until the patient's metabolism adjusts (usually no longer than a few days).
EXCESSIVE THIRST AND APPETITE - These side effects are annoying and may be permanent. If these side effects become too objectionable, the phenobarbital dose will have to be lowered and another medication added for seizure control.
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