Benadryl, anhydrosis, and One AC

[quietann]

Tl;dr: Benadryl can cause horses to stop sweating, so monitor them carefully.

I’ve learned something new. My mare has allergies, and after an unsuccessful response to Zyrtec a few weeks ago, I decided to try Benadryl (not on veterinary advice, just based on other people having success with it.) She was getting 15 25 mg tablets twice a day. I had a big bottle of the generic, and it ran out last weekend.

During the time she was on it, she was a little sleepy as expected. But I noticed, a few days before we ran out, that after a 5 mile ride (“long” for this horse), she was really tired, and her skin was very warm and she had not sweated, except under her tack. Oh no, I thought… Anhydrosis! Our former trail buddy, a Friesian gelding, was recently diagnosed and has to be kept in his stall with fans on, and can’t be ridden unless the temperature is below 70 degrees, so I was thinking DOOM!

I read up and decided to order some One AC, because it works for some horses and it’s inexpensive. She was started on it Thursday, 4 or 5 days after stopping benadryl, and on today’s ride, in high 70s, humid weather, she was not only more energetic (she wanted to canter… and go fast, not half-heartedly trot), she sweated! And her skin did not get warm at all.

So… was it the Benadryl causing the problem, and would she have sweated regardless of whether she got One AC or not, or is One AC a miracle supplement for her?

[lenapesadie]

I’ve heard of horses that stopped sweating while on Tri Hist. The one I knew personally resumed sweating after the Tri Hist was done; no other action. So, I’d suspect the Benadryl too in your shoes.

[horsepoor]

I had a horse that stopped sweating when on hydroxyzine and benadryl (separate occasions). The allergy specialist vet that prescribed the hydrox swore it could not be the cause, but then I found others here on COTH reporting the same thing. What I remember, and this was years ago, is that my horse was fine after a period of time off the antihistamines…I want to say maybe a week, maybe more? I did not use One AC or any of the other remedies (a bottle of Guinness a day is one IIRC). That horse has passed on, but I’m really careful about using antihistamines on any of my other horses now, and watch them carefully.

[Renn_aissance]

In humans, there is research indicating that anticholinergic drugs can inhibit sweating. This does include Benadryl and hydroxyzine. I’m not aware of equine studies.

Claritin, Allegra, and Zyrtec have a different mechanism. I consulted my horse’s personal pharmacist on this matter (aka my husband, a human pharmacist who did a veterinary rotation at VA Tech and kept all his books) and his advice was “you probably shouldn’t give your horse Benadryl, if he develops tolerance to Zyrtec again try Claritin.” My vet said that was a sound recommendation.

[Equibrit]

One AC is pretty much worthless. I bought a yearling who’s TB mother also suffered from anhydrosis.
I tried EVERYTHING without success including One AC. Horse loved his beer though.

Anhidrosis in Horses May Have Genetic Component - Kentucky Equine Research

" Considering the dearth of treatment options, lack of a cure, and strong suspicion that anhidrosis is genetic—the odds of anhidrosis are 22 times higher in horses with a family history of anhidrosis—Laura Patterson-Rosa, D.V.M., started searching for the genetic cause of anhidrosis to help eliminate it from the equine population, much like HYPP. To achieve this goal, Patterson-Rosa requires 200 samples submitted from owners of anhidrotic horses or offspring of anhidrotic horses by December 2016. For more information on anhidrosis and to submit samples, visit the Brooks Equine Genetics Lab website."

[quietann]

I’m planning to finish out the jar of One AC and then see what happens. I do know a few people who have had good results with it, though.

(Also, just because something has a genetic component doesn’t mean it can’t be treated. I’d be dead if that was the case!)

[cayuse]

I’ve had two stop sweating on me. One from hydroxyzine and the other for no reason. One AC helped both of them. The One AC worked better when I added a little salt in with their feed. I forget how much salt, just enough to get them drinking a bit more (they are a small pony and a mini so it wasn’t much). The one that stopped sweating from the hydroxyzine was the harder one to “re-set” and get sweating again, but he did come around and has been fine since.

[Anna.m]

As per my vet, I used Benadryl last spring when my vet was out, to combat an allergic reaction to the flies. I only gave 8 25mg tablets twice a day. (1000lb mare) My mare had no side effects from the medicine. But each horse can react to medicines so differently, I am glad to see your mare did much better on the One Ac

[quietann]

I guess it’s time for a one year update. I moved my mare 2 weeks ago to a place with 24/7 turnout, with sheds that have solar powered (!!!) fans. She has anhydrosis, and that was one of my worries - she would no longer have time underneath barn fans after being hosed down on really hot days. So this was a trial move.

At the same time, I started her on EquiWinner patches, which seem like some sort of voodoo… and they have helped a lot! It’s a 10 day protocol, and you can get your money back if they don’t work.

But they did! Here’s a photo from today, after a 30 minute handwalk on the local trails with her wearing a Cashel Quiet Ride fly sheet attached to a bareback pad. We have sweat!

Here’s her looking very fashionable on her walk, though the safety knot I tied to connect the top of the front piece to her halter was so safe it came undone. Oops.

[MsM]

Only those who have had a horse that stopped sweating can understand the joy of a sweaty horse!

I think my guy’s trigger was a response to drugs used for an MRI. He was wringing wet in a full body sweat right after. Since he was doing rehab, I didnt realize there was a problem until six months later when the weather was warm, he had graduated to trotting under saddle, and there was no sweat.

One AC helped a little. Acupuncture did not. It took Guinness stout to get a decent amount of sweat from him.

Swetworks from Horse Tech seems to work pretty well for him (though he doesn’t like the taste). His protocol in the summer now is night turnout and inside with fan during the day (whole stable). My barn only does supplements once a day so he gets about 3/4 serving Swetworks in his dinner. When I come out to ride I give him a beer mash of 1/2 bottle Guinness and a handful of his pellets to soak it up. He loves it! So far so good.

[lenapesadie]

Yay! I know that feeling of relief when you see sweat!

Is this her second summer with anhidrosis?

Knock on wood my boy is sweating really good this summer (his fourth w anhidrosis).

[quietann]

This is the second. Last summer it was scary. One AC helped a little. It’s helped a little this year but not enough.

Luckily I have no goals except to help her enjoy her retirement. If it’s a brutally hot day the barn owner or I can hose her off.

She is naked during the day except for the flymask and fly boots, and wears a flysheet overnight when there are lots of mosquitoes.

[lenapesadie]

I’m glad the EquiWinner patches are doing her some good!

I’ve used Refresh and felt that was very helpful. This year I’m doing One AC plus electrolytes. Pretty high doses of both tbh, but it’s working. He’s sweating normally and no signs of heat stress.

He’s got free access to the very airy barn w fans on when it’s quite hot now that he’s home and that’s been a good change from boarding.

Our first summer was also scary. Good to hear your girl is doing good! Sounds like she’s living her best life

[quietann]

I’ve heard it’s bad to provide extra electrolytes to a horse that can’t sweat them out. Mo idea whether that’s true but for now I’m not adding any extra ones. Luckily she drinks plenty of water.

[lenapesadie]

I haven’t heard that. Platinum Refresh has quite a bit of electrolytes in it. Different products do seem to work differently for different horses. I wish we knew more about anhidrosis in general. I haven’t tried that MegaSweat or whatever that Schneider sells. I think that product is Vit E based? Hope your girl continues to improve! Maybe it will get better each year.

[Renn_aissance]

@quietann, any chance you could tell us more about those solar powered fans? My barn’s trainer has researched them and hadn’t found anything he thought would be a good fit for the property layout. If these are newer on the market, perhaps it’s an option he didn’t see. He has made a project of running electricity to the run-ins in two of the fields but my fellow’s field is too far to make that practical.

My horse is continuing to sweat more or less appropriately for his level of exercise on Platinum Refresh. Knock on wood, that has been a good addition to his life for several years now.