Introduction: Previous studies have found higher rates of adherence in patients with type 2 diabetes mellitus (T2DM) using insulin pens compared to vial and syringe administration; however, little evidence is available to support this observation in elderly patients.
Methods: This was a retrospective claims database analysis of a predominantly elderly Medicare Advantage with Prescription Drug (MAPD) insurance population consisting of 3172 insulin-naïve patients with T2DM who initiated basal insulin using pre-filled pens or vial and syringe ('vial'). The index date was defined by the first pharmacy claim for basal insulin. Adherence, measured as proportion of days covered (PDC) and medication possession ratio (MPR), and persistence were evaluated in a 12-month follow-up period using an adjusted days' supply. Multivariate regression analyses and a Cox proportional hazards model were used to identify characteristics associated with adherence and non-persistence, respectively, and compare findings between the pen and vial groups.
Results: The pen cohort was slightly younger than the vial cohort (69.4 vs. 70.1 years, respectively; P = 0.0338). Similar proportions of male patients (53.3% vs. 56.8%; P = 0.0529) occurred in both cohorts, and lower Deyo-Charlson Comorbidity Index (4.4 vs. 5.0; P < 0.0001) was found for the pen cohort. Adjusted mean PDC was significantly higher in the pen cohort than the vial cohort (0.67 vs. 0.50; P < 0.001), as was mean MPR (0.75 vs. 0.57; P < 0.0001). Adjusted odds for adherence (PDC ≥ 80%) showed a positive association with use of an insulin pen (odds ratio = 2.19, 95% CI: 1.86-2.59). The adjusted risk of non-persistence (discontinuation) was significantly lower (58%) in the pen cohort relative to the vial cohort (hazard ratio = 0.42, 95% CI: 0.38-0.45). Key limitations include assumptions related to accuracy and comprehensiveness of claims data, and specifically days' supply data used to measure insulin adherence.
Conclusion: These findings suggest that pen devices improved insulin therapy adherence in a primarily elderly MAPD population with T2DM.
Funding: Novo Nordisk Pharmaceuticals, Inc.
Keywords: Adherence; Basal insulin; Elderly; Insulin detemir; Insulin glargine; Insulin isophane; Insulin-naïve; Pen; Type 2 diabetes mellitus.