Effect of adherence and insulin delivery system on clinical and economic outcomes among patients with type 2 diabetes initiating insulin treatment

Background: Adherence to insulin affects real-world health outcomes and may itself be affected by the choice of insulin delivery device (pen or vial/syringe). The choice of insulin delivery device may also have direct effects on effectiveness.

Objective: This study aimed to estimate the effects of insulin adherence and delivery device on real-world health outcomes.

Methods: This study included adults with type 2 diabetes mellitus initiating insulin, with continuous health plan insurance for 6 or more months before initiation (baseline) and 1 or more year after. Measured outcomes included glycosylated hemoglobin (Hb A1c) reduction, hospitalization rate, total health care costs, and pharmacy costs over 1 year of follow-up. Adherence (defined as having insulin fills sufficient for the entire quarter), pen or vial/syringe use, and disease-related patient characteristics were assessed in each quarter. To account for the time-varying relationship between adherence, patient characteristics, and outcomes, marginal structural generalized linear models were used to estimate the effect of adherence and device use. Mean outcomes were predicted for different combinations of adherence and device choice.

Results: Among the 13,428 patients (mean age 54 years; 46% women; baseline Hb A1c 9.3%), adherent pen users had greater reductions in Hb A1c (-0.35%; P = 0.045), lower hospitalization rates (-0.36; P < 0.01), and higher pharmacy costs ($2923; P < 0.01) than did nonadherent vial users, and similar total health care costs ($3906 lower; P = 0.1). Pen use and adherent vial use decreased hospitalization rate and increased pharmacy but not total costs.

Conclusions: Adherence and pen use have beneficial effects on patients' real-world outcomes, with the most favorable effects attributable to adherent pen use.