Safety and treatment compliance of subcutaneous immunotherapy: A 30-year retrospective study

Background: Safety and treatment compliance are still considered important shortcomings of subcutaneous immunotherapy (SCIT).

Objective: To assess the rate of side effects (SE) to SCIT and treatment compliance at a hospital medically supervised facility.

Methods: A retrospective review of patients with allergic rhino-conjunctivitis (ARC) with or without asthma, who received SCIT to mites and pollens from 1988 to 2018, was performed. The information was collected from patient's allergen immunotherapy forms that had been prospectically filled in by expert physicians.

Results: Two thousand two hundred patients (50.2% males; mean age 29.4 ± 11.7 years) received 3037 SCIT courses. A total of 91,187 injections were given, with a mean SCIT duration of 2.5 ± 1.9 years. Nine hundred fifty-seven patients (43.5%) were compliant as they completed the minimally required treatment duration of 3 years. A total of 1087 SE (1.2% of all injections; 76.8% local reactions) were reported in 513 patients (23.3%). There were 42 anaphylactic reactions (in 29 patients) during the study period; two of these were severe. Adrenalin was administered only once. No anaphylactic shock was reported. Only 39 patients (1.8%) discontinued SCIT because of SE, the majority of whom (24; 61.5%) because of systemic reactions (urticaria, asthma, anaphylaxis). Parietaria vaccines were the most frequently associated to SE. Female gender, number of vaccines administered (2 vaccine vs. 1 vaccine) and year of SCIT inception (1996-2018 vs. 1988-1995) were independently associated to SE.

Conclusion: SCIT, although not absolutely free of risk, is safe and well tolerated. There is still room for improvement of treatment compliance.