Introduction
Allergic skin diseases (atopic dermatitis, food allergy) are common causes of pruritus in cats (1-3). Management is often difficult due to the temperament of some cats and the adverse side effects associated with some medications (1-3). Treatment options include allergen avoidance, allergen-specific immunotherapy (ASIT: for atopic dermatitis), glucocorticoids, cyclosporine, antihistamines, essential fatty acids, and combinations of these (1-3). Allergen-specific immunotherapy is associated with few adverse side effects, and has been reported to be beneficial in 60% to 78% of cats with atopic dermatitis (1-4). Although ASIT is one of the most effective and specific treatment options for atopic dermatitis, many cat owners do not choose this therapeutic option due to financial concerns, their cat’s temperament not being amenable to injections, or their own fear of needles (trypanophobia).
Management with orally administered medications can be difficult in cats. Cyclosporine has been reported to be as effective as prednisolone; however, it is not registered for use in cats and should be avoided in cats with underlying viral disease or at risk for toxoplasmosis (5). Glucocorticoids are an effective and inexpensive treatment for atopic dermatitis, but are less reliable for food allergy (1-3). Although cats are fairly resistant to the adverse side effects of glucocorticoids, long-term and high-dose corticosteroid use are known to have the potential to potentiate insulin resistance, adrenal hormone resistance, cutaneous fragility, and may result in congestive heart failure (1,6,7).
Oral antihistamines are a viable treatment option for allergic cats and can be used for their steroid-sparing property (1-3,8,9). As in the human and canine patient, antihistaminic effect in felines is individualized and unpredictable. Trial courses of different antihistamines may be required. Published studies investigating the efficacy of individual antihistamines in cats with allergic pruritus are limited and include evaluation of chlorpheniramine (10), oxatomide (11), clemastine (12), and cyproheptadine (13).
Cetirizine is a second generation H1-receptor antagonist that is well-tolerated in dogs (14) and cats (15). Because cetirizine is known to affect eosinophil function, and eosinophils appear to play an important role in cats with allergic dermatitis, this antihistamine may be particularly beneficial in this species (1,16,17). Cetirizine acts as an inverse agonist and stabilizes the inactive conformation of H1 receptors (18). It also has non-H1-dependent activities such as inhibition of preformed mediators of inflammation such as histamine, tryptase, and leu-kotrienes from basophils and mast cells; inhibition of eosinophil chemotaxis; reduction of eosinophil survival; and alteration of adhesion molecule expression (17,19,20). All of these elements are involved in the pathogenesis of allergic inflammation. Cetirizine is nonsedating at therapeutic doses in humans due to efflux from the central nervous system via the P-glycoprotein pump system (15,21). Sedation can occur at higher doses in humans (15,21) and was reported to occur transiently in dogs (18). Sedation has not been reported in cats given cetirizine (15). Papich et al (15) found cetirizine to have a half-life of 10.06 h after oral administration in cats, allowing for once-daily administration in this species. This makes cetirizine a drug that can be administered by cat owners with greater compliance than drugs which require multiple daily dosing (15).
Cetirizine was found to be effective in 18% of dogs with atopic dermatitis in 1 small study (14). Although anecdotal information (3,16) indicates that cetirizine may be beneficial in the treatment of cats with allergic skin disease, we could find no published studies that corroborate or refute this information. The purpose of this paper is to report the results of an open clinical trial on the efficacy of cetirizine for the management of allergic pruritus in the cat.