Phenobarbitone testing

Re: Phenobarbitone testing

james herriot lied — Sun, 11 Nov 2012 21:26:51 GMT

[quote user="alison howell"]

Fair enough but with that history wouldn't you be thinking of dose reduction even if pheno levels were within the normal range? If the initial dose was higher, the levels would look normal, but the dog still wouldn't necessarily need the treatment?

[/quote]

Always to the first part. I think there are an awful lot of 'epileptic' dogs on life-long barbiturates where it was perhaps a transient or self-limiting set of initial events. When I was in permanent practice, I generally tried one wean off barbiturates when the lead-in to treatment had been mild or sporadic. First sign of trouble, back on treatment. Now I'm a locum, it's impossible to follow these patients up.

But we're not actually arguing opposites here: as most of these patients have a fairly steady state, i.e. the trough and peak levels are probably not very different, I prefer to go for the lower dose to see whether or not there's adequate drug in the bloodstream all of the time. If the trough level is close to the upper range, I'd certainly be doing a peak test to make sure we weren't overdoing things; conversely, I suspect that if your peak level was low in the range, you'd probably want to look at how low it got later that day.

When I was in college (before the availability of phenobarb testing), we were taught to give the lowest dose that allowed for a seizure every 4-6 weeks.

Re: Phenobarbitone testing

Ian Ross — Sun, 11 Nov 2012 19:26:53 GMT

I remember a BSAVA Congress lecture from a few years ago, and they posed the question "What are you going to do with the results?" So they didn't recommend testing as often in stable patients. I prefer to do peak levels, because then I think you know how much you can increase. If I had a really stable dog, I would just reduce the dose, I wouldn't worry about what its blood levels were.

Re: Phenobarbitone testing

vs0u — Sun, 11 Nov 2012 19:15:00 GMT

[quote user="james herriot lied"]I certainly do care if the dose is too low: I have a patient at the moment which was put onto epiphen back at the start of the summer, off the back of a couple of seizures in the same day. No seizures since the first tablet. Previous phenobarb - two months ago - was at 92%of lower therapeutic dose, and last week's at 62%. I therefore don't think that the dog necessarily needs to be on epiphen, and we're starting a slow wean.[/quote]

Re: Phenobarbitone testing

james herriot lied — Sun, 11 Nov 2012 16:46:07 GMT

[quote user="alison howell"]

But surely you are only interested in the peak value because as long as the dog is not fitting, you don't care if it's too low, only if too high, and if the dog is fitting you would want to increase the dose and therefore need to know if you safely can? The trough value wouldn't tell you that.

[/quote]

I certainly do care if the dose is too low: I have a patient at the moment which was put onto epiphen back at the start of the summer, off the back of a couple of seizures in the same day. No seizures since the first tablet. Previous phenobarb - two months ago - was at 92%of lower therapeutic dose, and last week's at 62%. I therefore don't think that the dog necessarily needs to be on epiphen, and we're starting a slow wean.

Re: Phenobarbitone testing

vs0u — Sun, 11 Nov 2012 16:25:36 GMT

[quote user="james herriot lied"]

A fairly steady state is supposed to be achieved in the vast majority of patients, but I'd take the view that the lowest blood level will be just before the next tablet, so that's the best time in any case.

[/quote]

Re: Phenobarbitone testing

james herriot lied — Fri, 09 Nov 2012 13:37:52 GMT

Re: Phenobarbitone testing

Rob Loxley — Fri, 09 Nov 2012 13:37:32 GMT

http://avmajournals.avma.org/doi/abs/10.2460/javma.2000.217.200?journalCode=javma (J Am Vet Med Assoc. 2000 Jul 15;217(2):200-4. Effect of timing of blood collection on serum phenobarbital concentrations in dogs with epilepsy. Levitski RE, Trepanier LA.)

Re: Phenobarbitone testing

Sarah Keir — Fri, 09 Nov 2012 12:59:50 GMT

I thought current thinking was that once steady state had been achieved, the timing of the test doesn't matter unless you are looking for toxicity?

Re: Phenobarbitone testing

James Laidlaw — Fri, 09 Nov 2012 11:33:09 GMT

I follow the Idexx stuff you've mentioned as they do our labwork.

Consistency is important so clients get used to doing the same thing each time depending on what you are looking for.