| Using sublingual immunotherapy to treat atopic dermatitis in canine veterinary patients
Consider oral allergen administration when treating patients with this skin condition to reduce reaction risk and achieve an optimal result.
By Thomas Lewis, DVM, DACVD
DVM360 MAGAZINE
The practice of desensitizing an allergic patient with sublingual drops of allergens instead of utilizing subcutaneous injections has been available in human medicine for many years, and it recently obtained FDA approval for the treatment of allergic rhinitis to certain grasses. Over the past several years, there has been more interest in and research done on this modality in veterinary medicine, giving the practitioner who treats atopic patients with immunotherapy a welcome additional option. Recent studies have demonstrated that the treatment is safe, and I personally find it effective in my own patients.
Benefits of sublingual immunotherapy
One obvious benefit of sublingual versus injectable immunotherapy is the fact that needles are not involved. Some needle-phobic clients (and patients) now have the ability to easily administer immunotherapy without the physical and emotional trauma of an injection. Because glycerin can have a slightly sweet taste, most dogs do not mind the administration of the product, which ideally is placed below the tongue and behind the mandibular incisors. Another significant advantage of sublingual over injectable immunotherapy is the higher margin of safety.6,7 Patients that experience adverse reactions to allergen injections should be considered excellent candidates for sublingual immunotherapy.6 In my practice, we've had several patients that exhibited anaphylaxis in response to either the intradermal allergy test or their injectable allergens that have not just tolerated but responded well to sublingual immunotherapy.
Another reason to consider sublingual immunotherapy is the fact that placement of the allergen sublingually can result in a different, possibly more favorable, immunological response.3,7,8 Patients that have failed to respond adequately to injectable immunotherapy may respond well to sublingual. The first patient I personally started on sublingual immunotherapy had been receiving injectable immunotherapy for nearly two years with only marginal improvement. The patient experienced significant improvement after less than 30 days of sublingual immunotherapy.
Dosing
In our practice, we do not use a diluted vial, but instead we start the first day with the more concentrated allergen vial averaging 20,000 protein nitrogen units (PNU) per milliliter (PNU/ml). We feel that the additional safety of sublingual immunotherapy also lends itself to this more rapid protocol schedule so that our patients may respond more quickly.
In the 12-month period from May 2013 through April 2014, the doctors at Dermatology for Animals have placed 910 patients on sublingual immunotherapy with the starting recommendation of 0.05 ml (one pump) of allergen administered once daily. Of these patients, four (0.44 percent) have experienced hives of the trunk, and one experienced vomiting. In one of these patients, the hives subsided and did not recur with subsequent dosing of the immunotherapy. Three of these patients tolerated the sublingual allergen when it was diluted 1:1 with glycerin, resulting in a 10,000 PNU/ml concentration. All three of these patients are currently doing well.
A notable adverse event rate of less than half of 1 percent is certainly an admirably safe protocol, especially when compared with the alternative therapeutic options—and again, this was without using diluted vials and an induction schedule. There have been a few more cases (approximately 15) in which the owners believed their dogs exhibited temporary (less than one minute) oral or facial scratching after the allergen was administered. When human patients react to sublingual immunotherapy with oral itch, one recommendation is to place the allergens in the vestibule of the oral cavity instead of sublingually, which might circumvent or minimize mast cell-related side effects of this type of immunotherapy.
When to use it
When starting a new patient on allergen-specific immunotherapy, I currently recommend the sublingual route as the initial protocol and will switch to injectable immunotherapy only if the patient is not achieving a positive response after eight months. Like many aspects of allergy and immunotherapy, the adage that "one size does not fit all" applies, and fine tuning of sublingual immunotherapy may be necessary in some patients just as it is with injectable protocols. Whereas some patients may require one pump 50 µl (0.05 ml), some patients respond more favorably to 0.1 ml daily, while others 0.05 ml twice daily. In human medicine, published protocols range from twice-daily dosing to once-weekly dosing and from year-round administration to preseasonal (starting one month before symptoms start and stopping at the start of the allergy season), coseasonal (start and end with the pollen season) or variations of the above. My own atopic dog is well controlled on an average of four doses per week.
In conclusion, the option to administer allergens in a sublingual format is an exciting treatment modality. Its higher safety level, ease of administration and potentially equal or better efficacy for many patients compared with conventional immunotherapy should lead to sublingual immunotherapy being recommended early as a treatment option for the atopic patient.
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