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Discussion on Equine Antihistamines

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Pamela Parker (Portunus)
Posted on Tuesday, Nov 7, 2000 - 2:02 pm:   Edit PostPrint Post

Hi all, after reading lots of articles and forum posts on everything from heaves/COPD to insect bites, I keep coming up with the question:
what are effective equine antihistamines and what are there indications/contra-indications?

Having had horses with COPD (dam) and chronic sinusitis (filly) and having lots of experience with equi-hist (tri-hist), azium, and prednisone (prednisolone is now recommended instead of prednisone), I am left feeling that there ought to be some other good medications that are effective while not being a corticosteroid (not good for young horses).

I see that Atarax (hydroxyzine) is now being used in horses and wonder whether Benadryl (diphenhydramine) might also be useful. I would like to have a discussion on dosage, effectiveness, sideffects, or the lack of information on any of this.

Thanks, I look forward to a good discussion. Pam
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Emily French (Jcsmoon)
Posted on Tuesday, Nov 7, 2000 - 5:15 pm:   Edit PostPrint Post

Pam- I have used childrens cherry flavored benadryl to counteract my geldings occasional allergy attacks. However he does not have COPD, he just gets "hay feaver" if I ride him through blooming scotch broom. It is fairly effective on these attacks of the "snot noses" if you get the dose right. I have also used it to reduce his reaction to repeated bee stings, which he seems to do several times a year. I don't know if it would be effective in treating what your dealing with. I will say that my horse quite enjoys his medicine... :0)
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Robert N. Oglesby DVM (Dro)
Posted on Wednesday, Nov 8, 2000 - 6:44 am:   Edit PostPrint Post

I feel the need to point out that medication is not the conrnerstone of treating COPD but environmental management is, see the article Diseases: Respiratory: COPD in Horses. The use of antihistimines for COPD has not been very beneficial in mine and others hands.
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Pamela Parker (Portunus)
Posted on Thursday, Nov 16, 2000 - 9:25 am:   Edit PostPrint Post

HI folks, thanks for responding and I guess I needed to be more clear. My reference to COPD and sinusitis was just to say that I have been involved with allergy issues for a while.

The mare that had COPD died a long time ago, when we had a lot less understanding of "heaves". Her daughter, my 15 YO brood mare, has sinusitis and that is well controlled with diligent dust control and occasional tri-hist.

My question was, and is, a more general one on equine antihistamines. What is out there that is effective and non-steroidal. Emily's note about benedryl was great, I was not sure if that drug was OK to use in horses. Do we just extrapolate the dosage based on the human dose?

Are there any other non-steroidal, effective anti-histamines that we know can be used in horses?

thanks again, I should have been more clear, sometimes I just get too chatty.
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anne hada
Username: Lamepony

Post Number: 4
Registered: 5-2003
Posted on Monday, May 26, 2003 - 11:46 pm:   Edit PostPrint Post

Dr. O: Can you explain to me why a vet might suggest using an antihistamine with isoxoprene to treat a lame horse on stall rest? He explained that the isoxoprene would help increase blood circulation but I don't get what the histane (sp?) would do... This was not my regular vet. It was a second opinion from a very well respected rodeo and track vet who says the horse has a soft tissue injury. Both vets agree on this but so far have not isolated exactly where the damage is. I am getting ultra sound on Wednesday. Regular vet says the isoxoprene is fine and gave it to me, but does not understand the antihistamine suggestion either. Have you ever heard of this as a treatment? On bute the horse looks normal but without he goes back to bobbing within 24 hours.
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Robert N. Oglesby DVM
Username: Dro

Post Number: 8456
Registered: 1-1997
Posted on Tuesday, May 27, 2003 - 6:09 am:   Edit PostPrint Post

Histamines are a component of inflammation so you would think antihistamines might be logical antiinflammatory therapy. But this is generally not true except in the specific cases of allergic disease and some types of respiratory infections. No there is no logic, that I am aware of, in using antihistamine for muscoskeletal injury. I think the work supporting the use of isoxsuprene is weak see Equine Medications and Nutriceuticals Miscellaneous Drugs Isoxsuprine.
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New Member
Username: ksojerio

Post Number: 1
Registered: 5-2007
Posted on Thursday, May 24, 2007 - 11:17 pm:   Edit PostPrint Post


My horse has had recurring hives for the last month. My vet thinks that when things stop blooming she will get better. He gave me dexamethasone to treat the eruptions and said I should try an oral antihistamine. On average, she is getting 10cc of dex about every 3-4 day.

I have been feeding a product that contains Pyrilamine Maleate U.S.P. 600 mg but it doesn't seem to prevent the eruptions. After researching your database I find that this is a fairly ineffective drug. Further reading indicates that she might benefit from benedryl. I understand the dosages that you describe, but wonder how long can she stay on benedryl before something adverse happens.

I asked about an interdermal skin test and he said he didn't do them on horses, but could refer me to a clinic 350 miles away! (We are in a very rural area of Arizona.) Would it be beneficial to request blood tests? It seemed to me that your article didn't think they would be very helpful either.

At this point I amk grasping at straws.
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Board Administrator
Username: admin

Post Number: 772
Registered: 12-1997
Posted on Saturday, May 26, 2007 - 9:36 am:   Edit PostPrint Post

Hi bbmother,
If you are not getting a quick response to your question we recommend you start your own post rather than place it at the bottom of someone else's discussion. Perhaps starting a new discussion in the article on Hives would be a good place and you will find it at, Diseases of Horses » Skin Diseases, Wounds, and Swellings » Bumps / Nodules / Warts / Tumors » Hives, Wheals, and Urticaria in Horses. For more on posting etiquette see, Help & Information » Welcome to The Horseman's Advisor.
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