Scratching a veterinary dermatology itch: What's the latest on allergen-specific immunotherapy?

"Ah, that's the spot ..." (adobestock.com/Sasa Stock)Allergen-specific immunotherapy (ASIT), a common treatment for hypersensitivity-related diseases such as atopic dermatitis, has been researched and utilized more extensively in dogs than in cats. In a recent article, Ralf Mueller, Dr.med.vet., DEVCD, DAVCD, chief of dermatology at Ludwig Maximilian University of Munich, outlined recent advances in ASIT use in small animal patients.

Intradermal versus serum testing

Until recently, intradermal testing was the gold standard for identifying allergic responses in dogs and cats; however, a similar treatment success rate is documented using allergen-specific immunoglobulin E (IgE) detection in the serum. Positive results on either test indicate IgE production against a specific allergen, rather than the clinical extent of the patient's hypersensitivity. So Dr. Mueller cautioned that skin or serum test results should always be interpreted in combination with patient history, physical examination results and clinical signs. He said it's also important to discuss realistic expectations of therapy with owners before performing diagnostic testing, as ASIT is not a realistic treatment option in all pets.

New administration routes

The most common method of ASIT involves subcutaneous injection of allergens administered in gradually increasing volumes and concentrations over several weeks to months. After this induction period, maintenance-level injections with a consistent dose are given every two to four weeks for several years. Dosing intervals are typically adjusted based on the patient's clinical response, including the development of adverse effects.

Existing studies show that, on average, two-thirds of dogs achieve good to excellent outcomes with subcutaneous ASIT, but alternative dosing routes have also shown promise in preliminary studies using a small number of canine patients. An oromucosal method consists of placing a small volume of allergen extract between the lips and gums once or twice a day. Intralymphatic ASIT involves injecting a small volume of allergen extract into the submandibular or popliteal lymph node on a monthly basis.

Another recently tested method involves “rush immunotherapy,” in which the induction phase of subcutaneous ASIT is completed in one day using hourly injections given after antihistamine administration. This form of therapy requires continuous monitoring and has resulted in anaphylactic reactions in people, although dogs appear to tolerate the treatment well with mostly nonsevere reactions, such as increased pruritus. Rush immunotherapy is generally restricted for unique cases, such as venom hypersensitivity, when rapid treatment is critical.

Dr. Mueller reported on one study in dogs that showed that maximum improvement was reached an average of 6.8 months after rush immunotherapy, compared with 9.2 months with the standard subcutaneous ASIT schedule. Rush immunotherapy has also been used successfully in cats to manage airway inflammation associated with feline asthma.

Safer adjuvants

Adverse reactions to ASIT are often attributed to the use of adjuvants in allergen extracts, particularly alum. Therefore, alternative adjuvants are now being tested in pilot studies, but larger studies are still needed to conclude on their safety and efficacy.

Reference

1. Mueller RS. Update on allergen immunotherapy. Vet Clin North Am Small Anim Pract 2019;41(1):1-7.

Dr. Stilwell provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting. In addition to her DVM obtained from Auburn University, she holds a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida.