Adherence, persistence, and health care costs for patients receiving dipeptidyl peptidase-4 inhibitors

Abstract

BACKGROUND: The dipeptidyl peptidase-4 (DPP-4) inhibitors are among the newer, yet more established, classes of diabetes medications. OBJECTIVE: To compare adherence, persistence, and health care costs among patients taking DPP-4 inhibitors. METHODS: Claims were extracted from Humana Medicare Advantage Prescription Drug (MAPD) or commercial plans for patients aged > 18 years with ≥ 1 prescription filled for a DPP-4 inhibitor between July 1, 2011, and March 31, 2013. The first prescription claim for a DPP-4 inhibitor established the index date and index medication; 12-month pre-index and post-index data were analyzed. The Diabetes Complications Severity Index (DCSI) was used to assess a level of baseline diabetes-related comorbidities. Adherence (proportion of days covered [PDC] ≥ 80%) and persistence (≤ 31-day gap) measures were compared before and after, adjusting for DCSI, pre-index insulin, age, and gender. Post-index costs (in 2013 U.S. dollars) were compared using general linear modeling (GLM) to adjust for pre-index costs, DCSI, pre-index insulin, age, and gender. RESULTS: Based on study criteria, 22,860 patients with MAPD coverage (17,292 sitagliptin, 4,282 saxagliptin, and 1,286 linagliptin) and 3,229 patients with commercial coverage (2,368 sitagliptin, 643 saxagliptin, and 218 linagliptin) were included. For MAPD patients, the mean age was 70-72 years, and females represented 50%-52% of patients. For commercial patients, mean age was 55-56 years, and females represented 44% of patients. Clinical indicators for patients on linagliptin showed a higher comorbidity level than sitagliptin or saxagliptin cohorts (MAPD DCSI 3.0 vs 2.4 and 2.2, P < 0.001; commercial DCSI 1.2 vs. 0.9 and 0.9, P < 0.001); a higher use of pre-index insulin (MAPD 22% vs. 15% and 14%, P < 0.001; commercial 18% vs. 11% and 10%, P = 0.003); and higher mean pre-index costs (MAPD $14,448 vs. $11,818 and $10,399, P < 0.001; commercial $13,868 vs. $9,357 and $8,223, P = 0.016). For the MAPD cohort, the unadjusted PDC was lower for linagliptin patients (67%) compared with saxagliptin (72%) or sitagliptin (72%) patients (P < 0.001). Significant differences were still seen when adjusted for covariates. Linagliptin patients were more likely to be nonpersistent (73%) than those on saxagliptin (65%) or sitagliptin (67%; P < 0.01 for adjusted and unadjusted comparisons). For the commercial population, there were no significant differences in mean PDC between the 3 groups (linagliptin 70%, saxagliptin 72%, and sitagliptin 74%; P = 0.096). Dichotomized comparisons of nonpersistence were significantly different (linagliptin 65%, saxagliptin 62%, and sitagliptin 57%; P = 0.010), although upon adjustment using a Cox proportional hazard model, no significant differences were found. When controlling for other factors, post-index adjusted health care costs were similar between the medication cohorts (MAPD: sitagliptin = $13,913, saxagliptin = $13,651, and linagliptin = $13,859; commercial: sitagliptin = $11,677, saxagliptin = $12,059, and linagliptin = $11,163; all P > 0.25). CONCLUSIONS: For MAPD and commercial populations, baseline patient demographics were similar between the 3 DPP-4 inhibitor groups, but the linagliptin group may have had more complex patients (higher pre-index costs, higher DCSI, and more use of insulin). For the MAPD population, patients on linagliptin were less adherent and persistent than patients taking sitagliptin or saxagliptin for all unadjusted and adjusted comparisons. For the commercial population, which was notably smaller, these differences were in the same direction, but not all were statistically significant. When controlling for baseline factors, 12-month post-index direct medical health care costs were similar between index DPP-4 inhibitors.