Review of Systemic Reactions to Subcutaneous Immunotherapy Based on Injection Schedule in a Single Allergy Practice

Subcutaneous allergen immunotherapy (SCIT) is an effective treatment for allergic rhinitis, asthma, and venom hypersensitivity. Although rare, severe, and potentially life-threatening systemic reactions (SR) such as anaphylaxis can occur. However, our knowledge of SR between SCIT buildup (standard and accelerated) is limited. This study aimed to compare SCIT-related reactions between standard buildup (18-shot or 30-shot) and accelerated buildup (cluster). We conducted a retrospective chart review for SCIT-related reactions between 2015-2020 at the University of Utah. Statistical analysis of descriptive statistics and significance determined via Fisher's exact test was conducted. 175 patients met our inclusion criteria. The average age was 38.3 (±14.8), ranging from 9 to 80 years old. Most patients were on the 18-shot buildup schedule. Twenty-seven of 132 (20.45%) patients on the 18-shot buildup experienced a reaction (P=0.04), and 3 of the 11 (27.25%) patients on the 30-shot buildup developed a reaction (P=0.73). Thirteen of the 32 (40.63%) patients on the cluster schedule developed a reaction (P=0.02). Ten of those 43 patients who had a reaction met NIAID criteria for anaphylaxis and required epinephrine. Five were on the 18-shot buildup, 2 were on the 30-shot buildup and 3 were on the cluster schedule. Our data suggest that patients on the cluster schedule had a significantly higher prevalence of reactions (40% of patients on this schedule had a reaction). There does not appear to be a significantly increased risk of SR with 18-shot or 30-shot buildup, and larger sample size is required to make further conclusions.