Subcutaneous allergen immunotherapy (SCIT) may be administered using several different schedules. This topic review will discuss the advantages and disadvantages of accelerated immunotherapy schedules and the indications for their use, and will provide several specific examples of protocols that have been used successfully for aeroallergen immunotherapy. Traditional SCIT schedules and accelerated schedules for Hymenoptera immunotherapy are discussed separately. (See "SCIT: Standard schedules, administration techniques, and monitoring" and "Rush and ultra-rush venom immunotherapy for Hymenoptera allergy".)
Terminology — SCIT is divided into two phases: build-up and maintenance.
●The build-up phase involves serial injections of increasing amounts of allergen. During this phase, tolerance to the allergen is gradually induced and the patient's immune response to the allergen is modified from a Th2 phenotype to a Th1 phenotype . In conventional SCIT schedules, the build-up phase involves one or two injections per week and lasts three to six months. Conservative and moderate examples of conventional SCIT schedules are shown (table 1 and table 2).
●The maintenance phase of allergen immunotherapy involves ongoing injections of an immunizing dose of allergen, usually at intervals of three to six weeks. During the maintenance phase, the immune transformation becomes complete. This phase is usually extended for a period of three to five years because shorter durations of treatment are associated with an increased likelihood of symptomatic relapse once therapy is discontinued .
Accelerated schedules of immunotherapy involve shortening the length of the build-up phase, while the maintenance phase remains the same. The length of the build-up phase depends upon the frequency of the injections and the incremental dose increase between consecutive injections. Thus, accelerated schedules either involve administering more injections per visit, increasing the dose more between consecutive injections, or both.