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usually ends up in the range of 0.2-0.5mg/kg every other day. The author has had no
problems dropping from the initial once daily dose to the same dose on alternate
days for atopic horses (in contrast to patients with immune mediated disease). Some
clinicians prefer to use an initial parenteral dose of dexamethasone – 0.02-0.1mg/kg;
oral dexamethasone can be administered thereafter, in the dose range of 0.01-
0.02mg/kg every 2-3 days.
In addition to laminitis, the other side effect concerns would be potentiation of
existing infections or increased susceptibility to infection, particularly opportunistic
respiratory infections. At the doses required for management of most allergic horses,
this does not present a big problem in the experience of the author.
Antihistamines:
Drugs that block the cellular receptors for histamine may be utilised in allergic
horses. In the UK there are no veterinary licensed antihistamines, but human
products are used off-label. The drug used most commonly by equine practitioners is
hydroxyzine hydrochloride; doses of 0.5 -1.5mg/kg every 8-12 hours are suggested
in the literature. Others that may be used in the horse are chlorpheniramine
0.25mg/kg every 12 hours and diphenhydramine 0.75-1mg/kg every 12 hours.
Doxepin hydrochloride is a tricyclic antidepressant with H1-receptor blocking
effects and has been reported to be useful in some pruritic horses at dose rates of
0.5-0.75mg/kg every 12 hours.
Antihistamines may be more effective for cases of urticaria than pruritus. Although
the systemic side effects of antihistamines may be of less concern than for steroids,
sedation and personality changes may occur and these drugs are not permitted in
horses competing under certain regulatory authorities. Recommended withdrawal
times should be checked with the relevant bodies for competition horses.
Essential Fatty Acid supplementation:
Administration of essential fatty acids (EFAs) has received a lot of attention in the
field of small animal dermatology with many publications endorsing the benefits of
various combinations of omega 3 and omega 6 fatty acids at various dose rates in the
management of allergy in both cats and dogs. These products may modify the
arachidonic acid inflammatory cascade, diverting pathways away from the
production of pro-inflammatory eicosanoids (prostaglandins, thromboxanes,
leukotrienes) and leading to production of less inflammatory or inhibitory mediators
such as PGE1. LTB5, PG-2 series, TxA3 and hydroxyeicosapentanoic acid (HEPE).
EFAs also have been shown to optimise skin barrier function in dogs and have been
shown to have an additive effect with antihistamines and a significant steroid-sparing
effect in atopic dogs.
There are a small number of publications concerning the use of EFAs in horses. An
open study of 14 horses with insect bite hypersensitivity that were given 20g daily of
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ACVSC Proceedings Dermatology Chapter Science Week 2005