Anhidrosis, hydroxazine and prednisolone

[jlphilli]

My horse developed anhidrosis this year, but being on OneAC got him sweating again. A couple of weeks ago he developed really bad hives that turned scabby (kind of a mix, actually). We tried changing everything under the sun in his environment, but it didn’t get better. He was on dex for about a week before the vet switched him to prednisolone and hydroxazine. They aren’t getting worse anymore, but not better either. Right now he seems to be exfoliating a bit.

The main problem is that he has stopped sweating completely while on these meds. Has anyone had this problem before? The vet claims none of the meds can do that. This is particularly alarming because it’s going to be 100+ in the upcoming week (and is now too).

We also had a few skin biopsies taken and are waiting on the results.

[caryledee]

There have been several threads on here in the past with links between antihistamines and anhidrosis. My own horse stopped sweating two years in a row after being on atropine for corneal ulcers. My opinion is that no one really knows what causes anhidrosis; so just because there have not been any studies done proving a link doesn’t mean that it is not possible that certain meds will cause this reaction.

Once they stop sweating, it is very hard to get it started again until the weather conditions change. I tried everything but just had to wait it out. Horse went inside during the day and was hosed before being ridden. Good luck; I know how frustrating this is!

[cayuse]

Yes. I have had this experience. Welsh pony developed anhydrosis after several doses of antihistimines. One AC was effective in restoring the sweating.

[SoonieOTTB]

my mare totally quit sweating on Tri-Hist last year (didn’t on AniHist the year before that).

It’s the antihistamine, take her off. The vets may say it can’t, but since I told barn buddies of my issues, I’ve heard loads of stories about it. Keep on with One-AC, inside during the day, and maybe add beer.

[jlphilli]

Thanks guys! His hives got a little worse today, so we decided (with this new information) to stop the hydroxazine since it’s not really doing much. The vet doubled his prednisolone in an attempt to just get a response, so we can then taper off. Biopsy results came back negative for bacteria and fungus.

How long did it take for those who stopped sweating on antihistamines to start sweating again? I have kept on with the OneAC through all of this and will continue to do so. Thanks!

[horsepoor]

Another one who has had a horse stop sweating while on antihistamines. My experience was that he went back to normal fairly quickly, like a few days or perhaps a week after stopping the antihistamines. Both hydroxazine and good old Benadryl did it to him.

[PiaffeN_Passage]

My gelding gets both Hydroxyzine and Prednisolone and I’ve never had any issues with him not sweating. knock on wood

[jlphilli]

[QUOTE=horsepoor;8194585]
Another one who has had a horse stop sweating while on antihistamines. My experience was that he went back to normal fairly quickly, like a few days or perhaps a week after stopping the antihistamines. Both hydroxazine and good old Benadryl did it to him.[/QUOTE]

Good to know, thanks! Hopefully he will start sweating in a few days.

@PiaffeN'Passage;8194877

My gelding gets both Hydroxyzine and Prednisolone and I’ve never had any issues with him not sweating. knock on wood

Maybe if a horse already has anhidrosis (or getting there) it has that affect? You’re lucky!

After the doubled dose of prednisolone last night, he was practically hive free this AM. Hopefully we can get this under control!

[horsepoor]

It has been my theory that the antihistamines would trigger non sweating in horses already predisposed to that – but that’s just my own theory based on the one horse being affected while my others have not. My vet at the time didn’t think the antihistamines had anything to do with it, but became convinced after we had it occur again, plus I had anecdotal evidence from others (such as reported here on COTH).

Hives and allergies can be so frustrating. I hope you are able to keep your horse comfortable.

[AA_Hunter]

Regarding your horse’s problem with hives–mine had what I thought were hives one summer, lots of scabby bumps, didn’t respond to dex. Apparently it was some type of folliculitis. A short course of SMZs cleared it up immediately–in fact there was a huge improvement after the first dose or two. Wouldn’t hurt to try it for a few days and see if it helps.

[Dune]

I have had one stop sweating on Tri-Hist, but never hydroxyzine. FWIW, no vet I’ve ever talked to has heard of this happening, but I’ve definitely heard of it from horse owners. Go figure.

[jlphilli]

[QUOTE=AA Hunter;8195167]
Regarding your horse’s problem with hives–mine had what I thought were hives one summer, lots of scabby bumps, didn’t respond to dex. Apparently it was some type of folliculitis. A short course of SMZs cleared it up immediately–in fact there was a huge improvement after the first dose or two. Wouldn’t hurt to try it for a few days and see if it helps.[/QUOTE]

The biopsy came back negative for bacteria or fungus, but since he is getting a little cellulitis on one of his back legs from fungus that was there before (which has gone out of control with all the steroids), he started SMZ’s last night. Hopefully it will help the remaining scabby-ness too!

It’s very interesting that so many vets are saying that AHs can’t or won’t cause non-sweating, but it seems like that’s not the case. Stuff like that is disturbing to me because it always makes me question vets, and I end up feeling paranoid. lol

[jlphilli]

So this is strange and awesome. We started tapering off the prednilisone after we got a response with 10 tablets. When we got down to 6, he started to break out again. At that time I got to thinking about differences/similarities between last year and this one, and it hit me that last year I was giving him MSM in his smartpaks. This year I removed it because I wasn’t convinced it was doing anything for him. I had some MSM on hand, so as an experiment I gave him a loading dose (20,000mg). The next day, no hives! Have been giving the MSM for the past two days and even though he is now down to 2 tablets of prednilisone, he is 100% hive free! I really never thought MSM was doing that much for his allergies, but I was wrong!

On the other hand, still no sweating yet. Tried doubling the OneAC. If he’s still not sweating after the show this week, I’m gonna try the equiwinner patches.

[rcloisonne]

Ask your vet for an IV shot of dormosedan. It usually triggers copious sweating in most horses. Keep in mind dormosedan is a powerful tranquilizer so your horse will be sedated for a couple of hours.

[jlphilli]

[QUOTE=rcloisonne;8201675]
Ask your vet for an IV shot of dormosedan. It usually triggers copious sweating in most horses. Keep in mind dormosedan is a powerful tranquilizer so your horse will be sedated for a couple of hours.[/QUOTE]

He had that when he got his skin biopsied, and sweat profusely. He just doesn’t sweat otherwise. Ironically the first time he had trouble sweating was after he got tranq’d for ulcer scoping. He sweat profusely and didn’t sweat after that. I wonder if the profuse sweating caused by those actually makes it worse for horses with anhidrosis.

[caryledee]

That is good to know about MSM. I have had my guys on it off and on for years but like you, I never felt it was doing anything. I tried the Equiwinner patches. They did not help, but I did get my money back from them. I’ve got my guy on Restore SR (KER Nutrition) and he is doing well on it. Sweat Again is another product that seemed to help; One AC did not help him. I hope you can find an answer!