Confused about ACTH stimulation test

[For Mugs]

Hi everyone. We are new to this forum and just recently diagnosed with Cushings. Mugs is about 10 years old and a Chihuahua/Terrior mix weighing in at 22-23 lbs. We will be starting him on 10mg twice daily Trilostane. This forum has already helped me decide on his treatment (I was leaning towards the natural remedies at first) and ask questions of his Vet. Right now I am confused about when his first ACTH stimulation test should be done after starting the Trilostane. I had read 10-14 days and I thought my Vet said that previously. The other day he said 3-4 weeks. So, what is the recommended time frame to have the ACTH stimulation tests done?
And how many hours after feeding and giving him the Trilostane should the ACTH begin? Most recent info I found was Dr Mark Peterson's blog dated Nov 2013 stating 2 to 4 hours.

Any and all advise is appreciated. Thank you ! Debbie For Mugs

[labblab]

Hello Debbie, and welcome to you and Mugs! :)

I think you are starting off at an excellent dosing amount given Mugs' weight. As far as the timing of the first monitoring ACTH tests, the official protocol of Dechra (manufacturer of brandname Vetoryl) is to perform the first test within 10-14 days after beginning treatment, and then to test again at the 30-day mark. Some vets do adhere very closely to that schedule, but we are aware that some vets are now opting to wait a bit longer before running that first test (like the 3-4 week mark as your vet is now suggesting). I suspect this may be due to the fact that cortisol levels typically continue to drift downward during the first month of treatment, so Dechra generally recommends that no dosing increases be made before that 30-day mark, regardless of the outcome of the 10-14 day testing. As long as a dog is started on a dose that is no greater than 1 mg./lb., and also as long as the dog is outwardly doing fine, I personally don't object to waiting that extra bit of time before testing, especially since the ACTH testing can be so expensive.

However, by waiting, the trade-off is that you don't have as early a warning if the cortisol level seems to be dropping too low on that initial dose. That's why you do need to go ahead and test sooner, regardless, if a dog appears unwell with symptoms that can be attributed to overdosing: vomiting, diarrhea, loss of appetite, lethargy. So you can talk about the testing time frame in greater detail with your vet if you have a preference to test sooner than he is currently recommending. Since you are the one paying for the testing, he should be agreeable to whatever you decide you feel is best.

There is also some variability in the timing of the testing window, too, depending upon who you talk to. Again, Dechra's formal recommendation is to perform the test 4-6 hours after the morning dosing with breakfast. Some other specialists prefer to test a bit sooner than that, like beginning 2-3 hours after dosing. According to Dechra, trilostane typically reaches maximum concentration in the bloodstream 1.5 hours after dosing, and has exited the bloodstream about 12 hours after dosing. The goal of the ACTH testing is to catch the cortisol level at the lowest point. Dechra likes to test at what is typically the mid-point of the maximum effectiveness; as you have found, others like to test a bit earlier. In this vein, I think the most important thing is to be sure not to wait any longer than 6 hours after dosing to complete the test, and to make sure that all subsequent tests are performed within the same time frame so that you are comparing "apples to apples" in terms of the results.

In case you have not already seen it, here is a link to Dechra's most recently revised U.S. Product Insert for Vetoryl:

http://www.dechra-us.com/files/dechraUSA/downloads/Product%20inserts/Vetoryl.pdf

Marianne

[For Mugs]

Thanks for your reply Marianne. I've been having trouble getting on the manufacturer's website but will keep trying.

Should I expect Mugs to stay at the Vet's all day? Thanks,
Debbie
For Mugs

[labblab]

I've had trouble getting on Dechra's site myself this evening. They must have it offline at the moment.

No, Mugs should not have to stay at the vet's office all day. The test itself should only take 1-2 hours, depending on the type of stimulating agent that they use.

Marianne

[Dawn Anderson]

Hello,

I would not wait 3-4 weeks after starting the meds to test, I would have the acth done in 2, not all dogs are the same, my girl weighed 91 lbs when we started her and the dosage was well below what the manufacture recommends. I would lean toward testing every 2 weeks till you know that the dosing is correct. By chance did they give you an emergency package of predisone just incase the levels drop down to fast and get to low??? Butters only had 1 Addison episode due to her dosage, which was only 15mg in am & 10 mg in the pm and that is a very low dose for a 91 pound dog.

Keep up the good work
Dawn & Miss Buttercup