Subcutaneous Allergen Immunotherapy
Specific allergen immunotherapy is considered to be the only potentially causal therapy for allergic diseases. This treatment is mainly administered by two routes, subcutaneous and sublingual. Subcutaneous injection allergen immunotherapy has been practiced for 100 years and includes the administration of increasing doses and then maintenance doses of extracts of inhalant and venom allergens.
Very well designed controlled clinical trials, and further revision of theses ( systematic reviews and meta-analyses) have established its efficacy in treating allergic rhinitis, asthma, and stinging insect sensitivity. Symptoms scores and need of rescue medication were significantly reduced when compared with placebo. New preliminary data has also suggested a favourable response in some patients with atopic dermatitis. Injection immunotherapy improves disease related quality of life in patients with seasonal allergic rhinitis. The response to subcutaneous injection immunotherapy is dose dependent.
Disease-modifying actions include blocking development of new sensitivities in patients sensitized to only one allergen, blocking progression to asthma in patients with allergic rhinitis, and persistence of treatment effects for up to 7 to 10 years after an initial course. There are significant risks associated with the use of injection immunotherapy including the rare occurrence of systemic adverse reactions and anaphylaxis requiring the use of adrenaline. The risk is greater in subjects with severe asthma and with accelerated dosing schedules.
However, this risk is greatly reduced when injection immunotherapy is administered in controlled clinical settings where patients are continuously monitored and, when necessary, treatment is promptly and effectively given. It is correct to conclude that allergen injection immunotherapy prescribed as a therapeutic intervention in suitably selected patients with allergic disease has established its efficacy, good safety profile and its role as modifier of the allergic disease.
Allergen specific immunotherapy (allergy vaccination), since its introduction in clinical practice 100 years ago, has ever been administered by subcutaneous injections. At the end of the 1980ties, however, some safety concerns stimulated the search for safer alternative routes of administration, and the sublingual route (SLIT) was firstly described in 1986.
After 25 years of intense clinical research, SLIT was accepted in the most important official documents as a viable alternative to subcutaneous injections. The current indications to SLIT are the same as with the traditional injection route (allergic rhinitis and allergic rhinitis with concomitant asthma), with the exception of hymenoptera venom allergy. In Europe (and many other Countries, but USA), SLIT is commercialised by several manufacturers, under different pharmaceutical forms (drops, tablets, monodose vials) and with slightly different schemes of treatment, but the general characteristics of the therapy remain the same. The vaccine has to be taken in the morning before breakfast, kept under the tongue for 1-2 minutes, and then swallowed. As with injections, the course of treatment starts with increasing doses, until a maintenance dose is reached.
Recently, it has been suggested that the updosing phase could be not necessary, and sometimes the treatment starts with the higher dose. According to the manufactures the maintenance can be taken daily or each other day. The recommended duration of treatment is 3 to 5 years. The main advantage of SLIT is its overall safety. Usually, side effects are limited to the mouth (oral itching or swelling) or to gastrointestinal tract (stomach-ache, nausea) and tend to disappear after the first doses. Severe systemic side effects have been described only sporadically.
The good safety profile makes SLIT an ideal candidate for the paediatric use. For the same reason, the use of SLIT is currently being investigated also for food allergies or hymenoptera hypersensitivity. Another advantage is that SLIT is managed at home by patients themselves. During the last years, the quality of allergen extracts for SLIT has much improved, and the optimal dosage has been defined at least for grass pollen. According to the most recent trials, SLIT seems to be able to maintain its beneficial effect for several years after the treatment has been stopped.
It must be remembered that, also for SLIT, a detailed diagnosis of IgE-mediated (allergic) disease is mandatory before prescription. In addition, it is good clinical practice to give the first dose under medical supervision, and to carefully instruct the patients about the scopes and modality of the treatment.