Systemic tolerability of specific subcutaneous immunotherapy with index-of-reactivity-standardized allergen extracts administered using clustered regimens: a retrospective, observational, multicenter study.

Background Subcutaneous immunotherapy is an etiological therapy for certain IgE-mediated diseases. It is usually administered in 2 phases: induction and maintenance. Administration in clustered schedules during the induction phase may be a valid alternative to reach the maintenance dose early if the treatment is well tolerated. Objectives To compare the tolerability of different clustered schedules in subcutaneous immunotherapy with standardized allergen extracts administered and to identify factors associated with increased risk of systemic reactions (SRs). Methods Retrospective, observational, multicenter study in patients with allergic respiratory disease. Results Data from 1,147 patients were collected. Thirty-nine patients (3.4%) experienced 42 SRs (0.6% of doses). According to the European Academy of Allergy and Clinical Immunology SR grading system, there were 7 grade 0 reactions (16.7%), 26 grade 1 reactions (61.9%), 8 grade 2 reactions (19.0%), and 1 grade 3 reaction (2.4%). There were no grade 4 SRs (anaphylactic shock). We observed a higher risk of SRs in patients who received an initial dose higher than 0.3 index of reactivity (IR); only 2 reactions occurred after administration of the initial dose of the regimen, both with 0.4 IR. The remainder appeared in subsequent injections, although never with a dose lower than 0.35 IR. Conclusions Clustered regimens with IR-standardized extracts are an alternative to classic immunotherapy thanks to their low incidence of SRs compared with other rapid regimens during the induction phase. The ideal clustered regimen should start at an initial dose no greater than 0.35 IR to minimize the incidence of SRs.