Decker, the 5 year old Golden Retriever
The set up...
Decker presented to me with a history of 3 seizures in the preceding 2 weeks. The seizures were consistent with generalized, tonic-clonic seizures of a duration about 30 seconds to 2 minutes (depending on the parent reporting the seizure). Decker was a very big boy. Not fat...just one of those super large Goldens that we occasionally see. He had a pretty healthy history prior to the seizures other than occasional ear and skin issues that the primary veterinarian had addressed. He wasn't on any current treatment, was up to date on vaccines, hadn't traveled out of Wisconsin in the last 6 months, did not have a history of head trauma and wasn't a working dog. Yes, I do ask all of those questions during a seizure consult, every time. Unless I forget. But I try not to forget.
The Exam...
Decker's exam was normal. Normal physical (other than his giant, wonderful self) and a normal neurologic examination. So his lesion localization was... (you fill in this blank. Look at the bottom to check your answer).
The Plan...
Decker needed anticonvulsants. More than 1 seizure every 3 months is a good reason to start anticonvulsant therapy according to the IVETF. So, we did! We started phenobarbital at about 4 mg/kg PO q12h and requested a serum phenobarbital concentration in 14 days.
The Serum Concentration...
14 days after starting phenobarbital the serum phenobarbital concentration was 22 ug/ml (reference range: 15-40 ug/ml)
What do you do with this information?
Well, to answer that question you must first ask yourself why you took the serum phenobarbital concentration in the first place? Was it...
1. To document that it was therapeutic for Decker?
2. To ensure it wasn't toxic?
3. To show if the client wasn't giving it right?
4. To document if the serum concentration was too low"?
How do you know if the dose was appropriate for Decker? You look at the seizure calendar which we cannot do until Decker has been on phenobarbital for at least 3 "seizure cycles". What is a seizure cycle? It is the interval between seizures. In his case, it is less than 2 weeks (3 seizures within 2 weeks). So, we must evaluate efficacy by looking at at least a 6 week interval of time.
Toxicity is seen by clinical adverse effects in the pet, which we cannot truly evaluate until the drug reaches steady-state. Steady-state is about 14 days in dogs, therefore signs of toxicity (or that the dose is too HIGH) should be assessed at the 14 day visit, or shortly thereafter. If adverse clinical effects are problematic after 14 days, the dose may be too high.
If the client isn't giving the drug, the serum concentration will be lower, but how much lower really depends on how often they miss a dose. This is not an appropriate way to ensure the client is giving the drug, in my opinion.
So, why take a serum concentration at all?? I do it to determine if the dose is too LOW. Serum concentrations below 15 ug/ml are outside of the accepted canine therapeutic range and therefore the dose should be increased. I would argue that serum concentrations below 25 ug/ml are clinically less desirable and typically advocate a dose increase for many pets (depending on clinical adverse effects).
What is the take away message?
Take the serum concentration to ensure it is not too low, use the dog to determine if the side effects are too high, and use the seizure calendar to determine if the dose is effective.
If any of this gives you anxiety - reach out! I'm here via email, telephone or a live consult and I am passionate about seizure management.
Merry Christmas to those of you celebrating this week! I wish you a safe, peaceful holiday and I look forward to continuing to work with you!