We may have reached the point in my horse’s life where he is no longer responding to Prascend. My vet has a call in to New Bolton’s endocrinology department but mentioned some potential next steps, including tapering down off of Prascend and trying trilostane instead. I’ve read some of the studies on this from 2004 or so which indicate that it does work to reduce blood cortisol measured by TRH test and may have fewer side effects than Prascend, but haven’t come upon anything more recent. That in itself gives me some questions (if it’s effective and has fewer side effects, why not use it in horses.) I wondered if folks here had tried it, or were aware of follow-up research to the Royal Veterinary College study in 2004.
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I’ve never heard of that so can’t offer anything, but was carbergoline mentioned? It’s working very well for some friends’ horses for whom Prascend or compounded pergolide were no longer doing the job.
Now I’m off to find out about Trilostane!
Some quick searching suggests it isn’t really used because the early study horses had additional management for symptoms, so the “improvements” really couldn’t be strongly linked to the drug.
But then
However, it is possible that concurrent use of pergolide and trilostane (currently not available in the United States) could produce a greater clinical response than use of pergolide alone.
Equine Cushing’s disease: Treatment and case discussions (Proceedings) (dvm360.com)
I didn’t find anything about any studies beyond 2003/2004
How’d you manage to get that URL to load? It looked promising from my Google search but 500’d when I hit it earlier.
We did not speak about cabergoline- I’m aware of it but we haven’t tried it. My vet was familiar with trilostane as she also has canine patients who use it but my fellow would be the first horse in her practice. I presume New Bolton’s endocrinology will provide good advice here!
I would have liked ONE of the blood panels that has been run on the humans and animals in my family in the last 2 months to have come back normal… but it wasn’t going to be this one for the horse! Maybe the cat’s follow up on Friday will be better.
It just came up 
I can’t wait to hear the report from NB on this.
The article didn’t seem to be discussing new research, only re-evaluating older research while contemplating new/additional/alternative treatment protocols. I saw several references to needing studies to not only compare Trilostane to pergolide (not sure why that didn’t seem to have been done?) but also to combining the 2.
Must have been a blip earlier, I did manage to get it up.
I was hoping that somebody would have looked at trilostane vs. pergolide at this point, too- that’s the research I was hoping I was missing (I hoped it was behind a paywall or something.) It makes sense to me to stack them- a lower dose of pergolide + trilostane- because they have different mechanisms. But I Am Not An Equine Pharmacist.
I work at a vet compounding pharmacy and we compound trilostane (as well as pergolide) and the trilostane caps sell very well. Though I have never seen it dispensed to any equine clinics, only to small animal clinics in use for dogs.
Of course our pergolide is ordered for horses all the time.
I did look up trilostane in our Saunders Equine Formulary (2006) for a quick reference and it stated that there were no reports of use with this preparation in horses. Licensed for dogs.
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I had a PhD friend check behind paywalls for anything on this, and she can’t find anything more recent than the 03/04 info, so think that answers your question!
It seems to have “failed” in that it appeared to only help cortisol levels, not ACTH. Maybe it has more use for IR horses?
That was something my vet mentioned as well- it doesn’t act on ACTH, only on cortisol. The way she put it, it sounded like we might be at the stage where his ACTH levels themselves are not responsive to pergolide, so we should switch the focus to managing the effects of high ACTH instead.
I asked about a dopamine infusion and I don’t think she thought I was funny. 
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I am bumping this because I really hate it when I look at a thread like this and no one has updated it in 3 years. And also for @JB, who asked.
We did not end up adding trilostane. His November and January tests showed that his ACTH was not under control of the pergolide, but in those tests, his cortisol levels were only slightly elevated. Since trilostane works on blood cortisol, it was felt unlikely to help him. New Bolton recommended that if he was otherwise clinically well we make no changes over the winter but test again in the spring and reevaluate. I felt like he was not himself but vet disagreed, and I have been gently reminded several times that in fact 27-year-old horses do start behaving like 27-year-old horses eventually, even if it takes them a whole lifetime to act their age. Anyway, we retested last week. Whereupon my horse threw out the most normal-looking set of bloodwork he’s had in 7 years, including a shockingly normal insulin, slightly low cortisol, and ACTH at “his normal” (50.) I asked my vet if she’s sure the sample came from the right horse, because I cannot reconcile this with what I’m seeing when I look at him. (Though we are going back on levothyroxine, and his thyroid levels could explain some of how he presents. Of course, so could the general state of being 27.)
Anyway, an interesting thing from New Bolton that may only apply to my horse and not to yours: we discussed cabergoline and NB advised that in his case they wouldn’t try it. The issue over the winter appeared to be tolerance to pergolide and they felt that the mechanisms of the drugs were similar enough that he would be unlikely to respond positively to cabergoline either.
Thanks for the update! From what I’m hearing “out there” the non-recommendation for cabergoline is common. I’ve only seen it used for horses who are tolerating pergolide but it’s just not managing their symptoms, and it works well. Nobody I know whose horse isn’t tolerating pergolide (well) not matter what they’ve done, has had any vet suggest cabergoline, for the very reason you said - the mechanisms are too similar.
So yay or a shockingly normal horse!
FWIW, my 32yo didn’t start acting/looking OLD until about 2 years ago, and in the last 2 years it’s like he made up for not looking/acting old for the previous 5 years LOL
That makes me feel better.
My sister used a good word to describe him. He is “muted”. He has always had a very big personality, interested in everything, always the center of attention, if he gets bored he might take down the barn to see how it works. These days… he’s sleeping. And he’s a little grumpy. And his hair coat is nowhere near his usual slick dappled glory. I hope that the levothyroxine will help him with these. In the meantime, he perks up when we go hack out, provided he does the steering and decides where we go… so we go. He pretty much does whatever he wants. I figure if being a certain age has to come along with hocks that don’t bend and eyes that don’t see, it also should get perks, like manes that haven’t been pulled in 10 years and a very high degree of judgment about how your life should be.
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