Non-fatal systemic reactions to subcutaneous immunotherapy: a 20-year experience comparison of two 10-year periods

Aim of the study was to evaluate in a retrospective analysis the incidence and clinical characteristics of nonfatal systemic reactions (NSR) to subcutaneous immunotherapy over a 20-year period (1981-2000) and to compare two ten-year periods as regard to NSR rate and type as well as to identify risk factors for NSR. On the whole, 435,854 injections were administered to 4,600 outpatients, following the suggested precautionary guidelines. In the first 10-year period, 115 NSR were observed (5.2% of patients and 0.06% of injections) and no fatalities, while 26 NSR (1.08% of patients and 0.01% of injections) occurred in the second 10-year period, with no fatalities. The difference was statistically significant (p<0.0001). Such a difference was mainly due to the reduction of asthma and urticaria (isolated or combined), (p<0.0001 comparing 1991-2000 with 1981-1990), while no significant difference could be found as regard to angioedema, rhinitis and other NSR. Almost all adverse events occurred within 30 minutes after injection and they were promptly controlled by standard therapy. NSR reduction was independent from the administered allergens. Female gender was the only clinical risk factor for NSR. Age, pollen season or manufacturer did not predict NSR. In conclusion, our data confirmed safety of subcutaneous immunotherapy and demonstrated that such a safety has increased during the last ten years.