DERMATOLOGY
The Truth About Antihistamine
use in the Allergic Dog
Andy Hillier, BVSc, MANZCVS (Canine Medicine), DACVD
Dana Liska, DVM, DACVD
Zoetis Petcare, Zoetis Inc
Antihistamine therapy is recommended and prescribed
frequently for the control of pruritus. While the use of
antihistamines may be well-intentioned, not only is the
recommendation misleading (because they are largely
ineffective), but it also has a potentially significant
negative impact on the skin disease, the care of the
patient, the owner’s perception of the care their pet
is receiving and the veterinarian-client-patient bond.
To illustrate the impact of chronic allergies on the
human-animal bond, one study reported 80 percent
of owners felt “sad” about their dog’s skin disease. 1
Do antihistamines effectively control
allergic itch?
NO. The recently published guidelines 2 for treatment
of canine atopic dermatitis from the International
Committee on Allergic Diseases of Animals (ICADA)
list antihistamines under “Interventions likely to be
of little or no benefit to treat acute flares of canine
atopic dermatitis (AD).” Four double-blinded placebo
controlled studies conclude a limited or lack of
efficacy. 3,4,5,6 Additionally, a clinical pharmacology
study, 7 a retrospective study, 8 a prospective clinical
study, 9 a single-blinded placebo controlled study 10 and
review papers 11,12 conclude a similar poor response
to antihistamines. And yet, antihistamines account
for almost 10 percent of all treatments dispensed for
pruritus by veterinarians; 13 plus, this does not take into
account treatment initiated by owners with over the
counter (OTC) antihistamines.
Do they treat a major inflammatory mediator
in atopic dermatitis?
NO. Previously, we thought atopic dermatitis was
a type-1 hypersensitivity response in which high
levels of IgE, mast cell degranulation and histamine
release were central to the disease process. We now
know this disease is much more complex, involving
many other cells in the immune system that release
proinflammatory and pruritogenic cytokines, such
as cytokines IL-2, -4, -6, -13 and -31. 14 None of these
cytokines are regulated by antihistamines.
Antihistamines work well in humans to manage upper
respiratory allergies. This is not, however, what we are
treating in dogs. Atopic dermatitis is more like human
atopic eczema, which is not treated with antihistamines.
Will antihistamines work in at least
some patients?
POSSIBLY. Antihistamines may provide a small and
limited benefit in some dogs. 2 It is not possible to
know if this minority of patients is responding to
antihistamines or whether this represents a placebo
effect. Regardless, response to antihistamines is the
exception rather than the rule.
What does this mean?
Antihistamines will provide no benefit for the vast
Issue 05 | NOVEMBER 2018 | 13