Continuing allergen immunotherapy for longer than one year should lead to a higher treatment success!

To ensure the maintenance of the readership’s interest, I propose to occasionally change the format of these monthly newsletters while still maintaining a "ˆbest-evidence” approach.

This month, I would like to share an article published by a group of colleagues in Barcelona. This paper, by Laura Ramió-Lluch et al., is entitled: “Allergen-specific immunotherapy in dogs with atopic dermatitis: is owner compliance the main success-limiting factor?”; its abstract can be found here.

What made me wish to summarize the results of this paper with you is that, to the best of my remembrance (and taking into account the increased limit of an aging memory) and after verification with a database search, this is the first article that establishes that the duration of AIT has a profound influence on treatment success in atopic dogs.

The records of 145 dogs with AD that were treated with AIT at 16 Spanish veterinary clinics were reviewed. All patients had been prescribed subcutaneous AIT, and the allergen composition of which was selected after allergen-specific IgE serology. Veterinary dermatologists then completed a 13-question form about the perceived success of the AIT, the medications still taken by the dog, and, in the case of AIT discontinuation, what were the perceived reasons behind it.

Altogether, 81 (56%), 14 (10%), and 50 dogs (34%) had been treated with AIT containing mites, pollens, or a combination of the two, respectively. Of importance is that the specific composition of the individual treatment did not appear to affect the AIT's efficacy, a finding that differs from previous studies.

Of the 145 dogs included, 36 (25%) had stopped the AIT injections before 12 months, while the other 109 (75%) had continued it beyond one year. This treatment duration allowed the easy segregation of the dogs into two separate groups that could be easily compared.

The main result of this study, shown in the figure below, is that a significantly higher treatment success (i.e., a higher reduction in the severity of clinical signs) was found in dogs receiving AIT for longer than 12 months compared to those treated for less than one year.

       (modified from Ramió-Lluch et al., Vet Record, in press 2020)

This reduction in the subjective owner-assessed clinical scores was also mirrored by a decrease in the concomitant medications still taken by the treated dogs. Indeed, in 87% of dogs receiving AIT for at least 12 months, the anti-allergic drugs were reduced or discontinued, while this had occurred in a significantly lower percentage (39%) of the dogs treated with AIT for less than one year.

These results' clinical implications are essential, as they highlight the need to carefully select the dogs—or perhaps I should say their "pet-parents"—before embarking on this lengthy treatment. This consideration echoes the recommendations of the first international guidelines for the treatment of canine AD (here), which specified as one of the AIT indications: “The dog's owners should be able to afford the time, expense and technical aspects of this regimen." Owner compliance is the key to success!

Another consequence, which mirrors the situation seen in allergic humans treated with AIT, is that the full immunomodulatory effects during AIT are likely to take longer than one year to appear, so an immunotherapy of a few months is only expected to be successful in a minority of dogs.

Are these conclusions transposable to cats and horses treated with AIT? On the one hand, we don't know for sure, as this has not been studied. On the other hand, as one has shown that a long AIT is needed to reach its optimal benefit in two different species (humans and dogs), one would think that the same duration is also likely required in cats and horses.

In conclusion, when deciding to do intradermal or serological testing before designing an individual AIT protocol, you should ensure that the owners are willing to continue the injections for at least a full year. If they are not ready to make this commitment, the only other recourse will be years of anti-allergic medication prescriptions, as AIT, is the only known intervention that might possibly lead to the complete withdrawal of anti-allergic drugs for their pet.

Respectfully submitted,

Thierry Olivry, DrVet, PhD, DipECVD, DipACVD

Research Professor of Immunodermatology

NC State University College of Veterinary Medicine, Raleigh, North Carolina, USA

Scientific Advisor and Dermatology & Allergy Consultant

Nextmune, Stockholm, Sweden