A new look at allergen immunotherapy because pets have allergies, too

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Canine atopic dermatitis (CAD) is a genetically predisposed inflammatory and pruritic skin disease with clinical features associated with immunoglobulin (Ig)E antibodies most commonly triggered by environmental allergens.¹ Feline atopic skin syndrome (FASS) is an inflammatory and pruritic skin syndrome of cats that may be associated with IgE antibodies activated by environmental allergens.² Small animal practices see patients with CAD and FASS often and many drugs are used for symptomatic therapy, however, the only definitive treatment is allergen immunotherapy.

Classical allergen immunotherapy (AIT) consists of subcutaneous injections of offending allergens in a solution. During an induction phase, owners administer increasing doses and allergen concentrations at short intervals of several weeks to months. This is followed by a maintenance phase, where a fixed dose is typically given at longer intervals.

Newer types of AIT include rush immunotherapy, where the induction phase is abbreviated, intralymphatic immunotherapy, and oromucosal or sublingual immunotherapy. AIT aims at inducing a regulatory T-cell response and downregulating the exaggerated immune response to offending allergens leading to allergy symptoms.

Before considering allergen immunotherapy, veterinarians need to discuss the costs, risks, and benefits of this treatment with owners. No reliable prognostic factor predicts the outcome of allergen immunotherapy early on, and it can take months to a year to see the maximal benefit. It is also important to note AIT is most suited for young animals with clinical signs for most or all of the year. Allergens for the allergen extract to be used for treatment should be chosen based on a positive reaction on the test and a history compatible with exposure to this particular allergen.³

Studies have shown approximately two-thirds of atopic patients eventually benefit enough to be considered a treatment success, which is usually an improvement in clinical signs of more than 50%. If after 12 months of allergen immunotherapy, there is no clinical improvement and no prominent decrease in required antipruritic therapy, then the patient is considered a treatment failure and immunotherapy is discontinued. If the patient is responsive to the treatment, owners have the option to continue AIT indefinitely, can gradually increase the time period between injections, or discontinue treatment after a couple more years.⁴

Allergic flares are commonly treated with drugs such as glucocorticoids, oclacitinib, and lokivetmab are short term. These drugs have fast onsets of action, and improvement of pruritus should be seen within days. Oclacitinib and glucocorticoids are typically administered for a few days to a week or 2. One injection of lokivetmab should be sufficient for an allergic flare. Combining oclacitinib and lokivetmab long-term with AIT is only recommended if patients are not responding to them individually. Most patients on a combination therapy of AIT and symptomatic medications will be treated with essential fatty acids, moisturizing shampoos, antihistamines, or topical hydrocortisone aceponate.⁵

Caitlee Callahan is a 2023 PharmD candidate at the University of Connecticut.

References

1. Outerbridge CA, Jordan TJM. Current Knowledge on Canine Atopic Dermatitis: Pathogenesis and Treatment. Adv Small Anim Care. 2021;2:101-115. doi:10.1016/j.yasa.2021.07.004
2. Bajwa J. Feline atopic syndrome - An update. Can Vet J. 2021;62(11):1237-1240.
3. Mallmann S, Klinger CJ, Classen J, et al. Clinical relevance of intradermal test results in atopic dogs. Tierarztl Prax Ausg K Kleintiere Heimtiere. 2021;49:349–356. doi:10.1055/a-1584-4965
4. Mueller RS. A systematic review of allergen immunotherapy, a successful therapy for canine atopic dermatitis and feline atopic skin syndrome [published online ahead of print, 2023 Mar 24]. J Am Vet Med Assoc. 2023;1-6. doi:10.2460/javma.22.12.0576
5. Olivry T, DeBoer DJ, Favrot C, et al. Treatment of canine atopic dermatitis: 2015 updated guidelines from the International Committee on Allergic Diseases of Animals (ICADA). BMC Vet Res. 2015;11:210. doi:10.1186/s12917-015-0514-6