In this sponsored VETgirl online veterinary continuing education blog, we review seizure control in dogs. How often should we "tolerate" seizures in our patients, and when do we start them on anticonvulsants? Which anticonvulsants should we start dogs on, and how much of a work up is necessary?
Today's VETgirl is a summary of a panel of neurologists who presented information at CVC 2016; this panel and VETgirl blog were sponsored by PRN.
A minimum database for a first-time seizure dog often includes a complete blood count, chemistry panel and urinalysis. ** Other diagnostics may include a lead (Pb) level in at-risk patients (e.g., those that live in a house with old paint, etc.), a bile acids (or ammonia) in young patients, and an electrocardiogram (to help capture an arrhythmia resulting in syncope). Dr. Simon Platt, BVM&S, MRCVS, DACVIM (Neurology), DECVN at UGA, recommends getting a video of the seizure episode as part of the preliminary workup also. As most pet owners have smartphones, a video may help the clinician differentiate syncope, sleep disorders, narcolepsy, or neuromuscular collapse from a seizure.
**Hey, before sending that blood out to your diagnostic lab of choice, please make sure to check a stat blood glucose (BG) so we know your patient isn't seizuring from hypoglycemia, ok?
Depending on the breed, age, sex and severity of seizures, advanced diagnostics such as CT, MRI and spinal tap (with appropriate fluid analysis of CSF, titers, etc.) may be warranted. This is especially important when infectious (e.g., toxoplasma, cryptococcus, Neospora), inflammatory (e.g., granulomatous meningoencephalitis, etc.) or neoplasia is suspected.
First time seizure
What about that first time seizure? Most neurologists agree that anticonvulsants do not need to be started with one seizure, as it may not be warranted unless additional seizures (or cluster seizures) occur. That's why obtaining a history is so important.
It's important to obtain a history to help identify the underlying etiology of the seizures. Questions may include:
- Is there a history of seizures in any of the siblings or parents?
- Any known toxicants (e.g., metaldehyde, garbage, moldy food, bromethalin rodenticide, strychnine, organophosphates, xylitol, mushrooms, blue-green algae, medications, etc.)?
- Does the dog roam unsupervised?
- Is there any construction going on now (e.g., painting, etc.) or risk of lead exposure?
- Has the dog ever shown abnormal mentation (e.g., star gazing, head pressing, etc.)?
- How long did the episode last?
- Did s(he) lose consciousness? Paddle? Urinate or defecate? How long did the episode last?
- When was the last time this happened?
- How long as s(he) out of it afterwards?
Appropriate communication with pet owners
As seizures are very scary for pet owners to see, it's important to calm the pet owner down and empathize with them about the stress-related to the seizure. It's also important that we veterinarians have a strong "seizure" talk, as pet owners should be educated on the preliminary diagnostic workup, whether or not to hospitalize their dog overnight for monitoring, whether advanced diagnostics are warranted, or when to start anticonvulsants. It's also important to discuss the dangers of additional or cluster seizures affecting the seizure threshold and how compliance is important to manage the seizures. Reassuring the pet owner that their dog’s personality is not going to change is important, while also reassuring them that the anticonvulsant therapy side effects are typically short-lived (e.g., several days to weeks) and may improve with time.
When to start anticonvulsants
Most neurologists agree that anticonvulsants should be started to prevent seizures from occurring more than every once per 3-6 months. However, if a dog presents for first-time seizures and is clustering (having more than 2-3 seizures in a 24 hours period), and metabolically appropriate (e.g., doesn't have hepatic encephalopathy, isn't hypoglycemia), then anticonvulsants should be promptly started. Likewise, in certain breeds known to have more severe seizures (e.g., Border collies, Australian shepherds), some neurologists would be more aggressive starting anticonvulsant therapy immediately.
Follow up blood work
Depending on the anticonvulsant that is started, follow up blood work is warranted. For example, with potassium bromide and phenobarbital, blood levels should be monitored. While this isn't yet readily available in veterinary medicine for levetiracetam (Keppra. We'll call it Keppra from now on because really, who can pronounce levetiracetam) or zonisamide yet, it may be in the future. As for phenobarbital levels, it is well known that if levels go above 35 mcg/ml, the risk of hepatotoxicity increases. Based on the ACVIM Consensus Statement of seizure control, phenobarbital levels should be checked ideally 2 weeks after starting - or adjusting - phenobarbital. Some neurologists advocate for rechecking phenobarbital levels 1 month later, and again every 6 months thereafter (along with a CBC and chemistry).
However, when it comes to doing blood work, be practical. In the words of Dr. Simon Platt "If the dog is too sedate it doesn’t really matter what the level is; if you think that it is due to that drug, it needs to come down. If the seizures are too frequent for you or for the owner of the dog, then it doesn’t matter what the level is; we need to do something different. So taking levels are important... but then there is also a sliding scale of how we are going to use them and when we are going to take them." Word.
Which anticonvulsant should you reach for?
Depending on which neurologist you talk to, or what school you trained at, you may pick or choose different anticonvulsants. This should also be based on the owner's decision and risks or compliance factors (e.g., can they dose once a day with bromide or three times a day with levetiracetam, can they afford one drug over another)?
One advantage of bromide over phenobarbital is that it is less expensive and only requires one-time-a-day dosing, so is beneficial in noncompliant clients who have safety concerns about phenobarbital and the monitoring regimen or blood work monitoring. Another benefit is not only the frequency of drug administration (once a day), but the long-half life of bromide; if an owner accidentally misses a few days, therapeutic levels should still be maintained. With phenobarbital, it's one of the oldest anticonvulsants out there and considered to be very effective; however, does require monitoring of serum levels to prevent dose-dependent toxic effects. However, some neurologists opt to use another anticonvulsant in agility dogs (so hindlimb ataxia isn't seen) or in dogs with gastrointestinal disease (e.g., pancreatitis, inflammatory bowl disease, etc.) to prevent adverse effects noted by the owner.
When to ask for a second anticonvulsant
In some dogs, the additional use of an anti-convulsant may be necessary. However, it's important to prepare clients appropriately, as anecdotally, the chance of that second drug making the patient seizure-free is about 3%. While a second anticonvulsant may be necessary, pet owners should be educated that additional drugs will not typically resolve the seizures (to prevent frustration by the owner). Additional anticonvulsants are warranted when there is a serious seizure focus and when seizures are still poorly controlled. What's important to consider when adding on a second anticonvulsant is whether that first drug is going to impact your second drug choice. Some neurologists may choose to start with phenobarbital and add bromide as a second anticonvulsant, while others may start with levetiracetam and add on zonisamide. Keep in mind that bromide doesn’t necessarily have to be used at a higher dose with phenobarb because there are no metabolic interactions with these two drugs; however, if you choose levetiracetam (Keppra) and/or zonisamide, then those two are going to have to be used at a higher dose if you are on phenobarbital. As with considering a first anticonvulsant, it's important to look at multiple factors such as owner compliance, financial limitations, safety, how efficacious the might be, the cost of it, how often it needs to be given, etc.
When in doubt, as an veterinary emergency critical care specialist, I always recommend that pet owners follow up with a board-certified neurologist. This is important to help compliance with long term monitoring, follow-up and care for seizure patients!
Today's VETgirl online veterinary continuing education blog is a summary of a panel of neurologists who presented information at CVC 2016; this panel and VETgirl blog were sponsored by PRN.