Assessment of basal insulin adherence using 2 methodologies among Texas Medicaid enrollees with type 2 diabetes

BACKGROUND: Basal insulin is often recommended as the initial therapy for patients with type 2 diabetes who require insulin treatment. Adequate adherence is critical to diabetes management, yet suboptimal insulin adherence has been reported. Second-generation long-acting (SGLA) insulin has higher dosing flexibility and lower hypoglycemia risk and may improve adherence. However, little is known regarding adherence to SGLA insulin and how adherence to SGLA insulin compares with intermediate-acting neutral protamine Hagedorn (NPH) and first-generation long-acting (FGLA) insulin. Measurement of insulin adherence is challenging because of the inaccuracies of recorded days supply of insulin, and traditional medication possession ratio (MPR) may be negatively affected. Adjusted MPR (aMPR) has been developed in an effort to address this issue. OBJECTIVE: To examine the unadjusted and adjusted associations between basal insulin type and adherence to basal insulin using MPR and aMPR. METHODS: This retrospective database study used Texas Medicaid prescription claims from January 1, 2014, through June 30, 2017. The index date was the date of the first basal insulin prescription without the same prescription 6 months before (pre-index), and all patients were followed for 12 months (post-index). Patients aged 18-63 years with ≥ 1 pre-index prescription of an oral hypoglycemia agent (OHA) or a glucagon-like peptide-1 receptor agonist (GLP-1 RA), without any post-index prescription of premixed insulin or a basal insulin different from index insulin, and with continuous enrollment throughout the pre- and post-index periods, were included. The dependent variable was basal insulin adherence over 12 months, measured using MPR and aMPR. Unadjusted and adjusted adherence comparisons were conducted by basal (background) insulin type (NPH, FGLA, and SGLA). Covariates included age, gender, baseline use of basal insulins and comorbid medications, total number of medications, OHA adherence, post-index number of OHAs, and use of bolus insulins and GLP-1 RAs. Analysis of variance, chi-square tests, and multiple logistic regression analyses were performed. RESULTS: Of the 5,034 patients included, NPH, FGLA, and SGLA insulin users accounted for 3.7%, 89.8%, and 6.5%, respectively. The overall mean (SD) age was 50.9 (9.9) years, and 65.9% were female. In the unadjusted bivariate analyses, SGLA insulin users had significantly higher adherence, using either MPR (SGLA 0.68 [0.25] vs. FGLA 0.59 [0.27] vs. NPH 0.55 [0.27]; P < 0.0001) or aMPR (0.83 [0.23] vs. 0.78 [0.26] vs. 0.73 [0.28]; P = 0.0001). After controlling for covariates, insulin type was not significantly associated with the likelihood of being adherent (MPR or aMPR ≥ 0.8) using either measure. CONCLUSIONS: Adherence to SGLA insulin was not different from adherence to other basal insulins after controlling for patient characteristics. Yet, MPR and aMPR have limitations and warrant further confirmation of the study findings. Before new adherence measures for insulin therapy are developed, MPR and aMPR should be used with caution.