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by Deborah H. Clark, RPh, PCCA Clinical Compounding Pharmacist
Canine atopic dermatitis, or allergic skin disease, is one of the main reasons dog owners visit their veterinary (vet) clinic.1 Much less is known about allergic skin disease in feline patients.
Compared to human patients with eczema or canine patients with atopic dermatitis, cats typically present varying clinical signs. Testing cats for serum allergen-specific immunoglobulin E (IgE) does not always indicate IgE prominence; skin barrier function in cats is not well known and even clinical signs can vary from cat to cat and from year to year.
Feline atopic skin syndrome (FASS) is a subclassification of a broader condition: feline atopic syndrome (FAS). FAS contains a spectrum of hypersensitivity disorders with various presentations that may affect the skin, gastrointestinal and respiratory tracts.2 FAS affects 12% of cats, usually within the first three years of life; 22% of these cats may exhibit onset of signs after age seven.3
FASS involves inflammatory reactions that are like those seen in canine patients. T cells are involved as well. The most commonly affected areas in FASS cats are the head and the ventral area (the belly or chest). In 70%, allergen specific IgE was detected, suggesting involvement of an allergic component; 50% of FASS cases have no secondary bacterial infection.
Secondary bacterial infections in these cats may be challenging for a vet to diagnose because they present very differently from dogs and humans. In many cases, the presenting signs are so close to those of other allergic types that a secondary bacterial infection may get overlooked. Adding to the complexities, fungal dysbiosis with Malassezia can also be present.
Regardless of the cause of the allergy — be it fleas, other parasites, food or environment — FASS cats may present a variety of reaction patterns. For example, FASS can present allergic rhinitis, asthma or conjunctivitis; in some cases, all three. Cutaneous signs can include head and neck pruritus, self-induced hair loss or “fur-mowing.” Fur-mowing can involve the entire ventrum down through the inside of the legs, giving the appearance of “cats with no pants.”
Other cutaneous signs include eosinophilic granuloma complexes and miliary dermatitis (eosinophilic papulocrustous dermatitis). Some FASS cats exhibit indolent ulcers around the mouth, while others may show granulomas inside the mouth or within the throat. As stated earlier, these signs can occur alone or in combination, can change from season to season or simply appear as signs worsen.2
Once other conditions are ruled out and diet or environmental modifications tried and failed, medical therapy is normally instituted to gain control of the condition. After clinical signs are controlled, the vet may offer the option to conduct allergy testing and institute allergen-specific immunotherapy. Some cat owners, however, are not willing to commit to this.
Cyclosporin is the only FDA-approved medication for the treatment of FASS. Cyclosporin is dosed at 7 mg/kg PO every 24 hours for 4-6 weeks or until resolution of clinical signs. Once achieved, medication is typically tapered to the lowest effective dosage due to the increased risk of developing diabetes mellitus (DM) and gingival hyperplasia.4
A manufactured product, Atopica®, is available for cats and, per the FDA’s Guidance for Industry (GFI) #256, must be considered first by a vet. The vet may choose a compounded formula if they have a valid reason that Atopica cannot be used in the individual feline patient. Fixed oil suspensions with this API are not recommended.
Antihistamines may be given as a treatment adjunct due to their steroid sparing effect but have limited efficacy.2 Corticosteroids, such as prednisolone, may also be administered.
When cats cannot be pilled, prednisolone oral solution or suspension is an option. Several manufactured human oral solutions and suspensions exist and, per GFI #256, must be considered before compounded preparations. However, some of these products contain alcohol — which is toxic to cats — while others contain flavoring that a cat may reject.
Another potential issue is the high-volume dosing required with commercial medications, which many cat owners find impractical and/or impossible to administer.
Remember to also look at excipients for species toxicities when considering manufactured drug products as a therapeutic option.
PCCA members with clinical services access may contact our Clinical Services team for help with compounding for FASS patients and other compounding concerns.
A version of this article originally appeared entirely in PCCA’s members-only magazine, the Apothagram.