Compliance in subcutaneous and sublingual allergen immunotherapy: A nationwide study

Introduction: Allergic rhino-conjunctivitis is a highly prevalent condition. In moderate to severe cases, allergen immunotherapy (AIT) is a cost-effective therapeutic option. Previous data have reported a large difference in treatment compliance of subcutaneously (SCIT) and sublingually (SLIT) administered AIT. Methods: By use of the unique civil registration number assigned to all Danish citizens and the Danish National Health Service Prescription Database, compliance rates of all patients prescribed with grass pollen AIT from January 1998 until December 2016 were analysed annually during the three-year treatment period. Results: The male/female ratio was close to 1:1 in SCIT, while SLIT was more frequently used by men. A large proportion of users was children or adolescents (32% and 45%, SCIT and SLIT, respectively). Compliance of both subcutaneous and sublingual treatment gradually fell each year; compliance in year 3 was 57% and 53% for subcutaneous and sublingual treatment, respectively. Compliance of grass pollen sublingual treatment was also analysed each year after registration on the Danish market. Compliance significantly increased following the introduction and stabilised on a relatively high level. Conclusion: Based on previous studies, we hypothesised that AIT compliance would be low, especially in SLIT. However, in Denmark, compliance in SCIT and SLIT was almost similar, and the majority of patients completed the three-year treatment period with a compliance in the last quintile.