Sublingual immunotherapy: A new option for allergy patients
The potential lifelong benefits of ASIT—whether given through injections or drops—make it a preferred treatment for atopic dermatitis that should be discussed with owners early in treatment.
ALLERGY SHOTS VS. DROPSThere are many similarities between SLIT and allergy injections. Like injections, SLIT formulations are typically supplied in three bottles of increasing concentration. The cost of SLIT vs. injections is about the same, typically costing a client $40 to $50 a month. Concurrent medications (e.g. antihistamines, corticosteroids, cyclosporine) do not appear to interfere with the efficacy of injections or drops and are often given during the initial few weeks to months of immunotherapy treatment, while waiting for the injections or drops to become effective.
Practical differences include the specific ingredients: SLIT is not merely an oral administration of the saline-based allergy injection mixture. It is formulated differently, and commercial preparations typically include proprietary ingredients to stabilize the allergens and promote mucosal absorption. Depending on the supplier, stabilizers may allow for the addition of protease-containing mold allergens to the mixture and sometimes for room-temperature storage.
The mechanism by which SLIT works differs from that of injection ASIT, involving the absorption of allergens through the oral mucosa with uptake and processing by specialized oromucosal dendritic cells, which direct the immune system toward immunologic tolerance of the relevant allergen.3
Another practical difference is administration frequency. SLIT formulations are typically administered every day, often several times a day, for the duration of therapy with no tapering.
Since both allergy injections and allergy drops are effective, selection for individual patients can be made mostly based on client factors (see "Shots or drops? Considerations when selecting injection vs. sublingual ASIT for dogs").
EVIDENCE OF EFFICACY
Studies of SLIT in dogs are only just being reported and largely consist of uncontrolled trials. A small, open trial of atopic dogs with dust mite allergy treated with SLIT reported 80% clinical benefit. The benefit was usually accompanied by measurable immunologic changes, including significant increases in allergen-specific IgG and decreases in allergen-specific IgE.4,5
Another study reported some SLIT efficacy in a laboratory model with sensitized beagle dogs, including significant changes in antiallergic cytokines such as transforming growth factor beta and interleukin-10 in treated animals.6
In my clinical experience in an open trial with a specific product (Allercept Therapy Drops—Heska), about 60% of dogs with atopic dermatitis that have not been treated with ASIT previously will have substantial improvement of their clinical signs after being treated with this formulation, as judged by veterinarian evaluation of response.7
The response rate for dogs that previously failed to respond adequately to ASIT may also be substantial. In these open trials, about 50% of dogs that were "shot failures" because of lack of efficacy, difficulty with administration, or anaphylactic reactions were successfully treated with SLIT.7 That is consistent with experimental evidence that shows that the mechanism of SLIT is different than that of injection immunotherapy.3,8