Systematic review of real-world persistence and adherence in subcutaneous allergen immunotherapy

Given that subcutaneous immunotherapy (SCIT) adherence in the literature is often studied in closely monitored trials, few studies report real-world SCIT adherence. The purpose of this review is to assess SCIT adherence in real-world settings.

A literature search of PubMed, Embase, Cochrane Library, Web of Science, and Scopus for real-world studies examining SCIT adherence was performed. Paired investigators independently reviewed all articles. For this review, "persistence" was defined as continuing therapy and not being lost to follow-up after initiating SCIT, and "adherence" defined as persistence in accordance with prescribed SCIT dose, dosing schedule, and duration. Article quality was first assessed using a modified Newcastle-Ottawa scale and then converted to Agency for Healthcare Research and Quality standards (good, fair, and poor).

The search yielded 1596 nonduplicate abstracts, from which 17 articles (n = 263,221 patients) met inclusion criteria. Fourteen (82%) studies reported persistence rates, ranging from 16.0% to 93.7%. Seven (41%) studies reported adherence rates, ranging from 15.1% to 99%. Five (29%) studies (n = 416 patients) collected original data on reasons for discontinuing SCIT, of which inconvenience was most cited. All studies were Oxford level of evidence 2b and of good (n = 10) to fair (n = 7) quality.

Real-world SCIT persistence and adherence rates are poor, with the majority of included studies reporting rates <80%; however, they range widely, explained in part by inter-study differences in measuring and reporting adherence-related findings. Future studies on SCIT adherence may benefit from following concordant definitions of persistence and adherence in addition to standardized reporting metrics.