Many clinicians and pet owners are familiar with allergen-specific immunotherapy (ASIT)—commonly referred to as allergy injections or allergy shots—for the treatment of atopic dermatitis in dogs and cats. The newest variation on this treatment is orally administered ASIT
called sublingual immunotherapy (SLIT)—or allergy drops. SLIT is administered through a metered pump dispenser that delivers a few drops of allergen solution onto the mucosa under
and around the tongue (Figure 1). This client-friendly method is widely used in Europe to treat allergic respiratory disease and, more recently, atopic dermatitis
in people.1,2 It has recently become available for animal use in the United States.
1. Sublingual immunotherapy formulations (allergy drops) are administered by using small, metered pump bottles that dispense
a small volume of allergen solution onto the oral mucosa. Here, the drops are administered to William.
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. DROPS
There 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
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