The Association Between Adherence to Insulin Therapy and Health Care Costs for Adults with Type 2 Diabetes: Evidence from a U.S. Retrospective Claims Database

BACKGROUND: Research has shown that many patients with type 2 diabetes (T2D) are not adherent to their medication regimen. OBJECTIVE: To examine the association between adherence to insulin therapy and all-cause health care costs for patients with T2D. METHODS: This study used the IQVIA PharMetrics Plus Linkable to Ambulatory Electronic Medical Record data from January 1, 2012, through September 30, 2017. Patients were included if they were identified with T2D and initiated therapy on basal insulin (BAS) or basal-bolus (BAS-BOL) combination at any time from January 1, 2013, through October 1, 2016. Patients aged < 18 years, who used an insulin pump, identified as pregnant, or did not have continuous insurance coverage from 1 year before initiation on insulin therapy through 1 year after initiation were excluded. Descriptive statistics compared patient characteristics and costs (in U.S. 2017 dollars) between patients who were adherent or nonadherent to their insulin therapy in the 1-year postperiod, where adherence was defined as having proportion of days covered (PDC) of at least 80%. In addition, generalized linear models were used to compare costs between adherent and nonadherent patients, while controlling for patient characteristics, previous general health and comorbidities, resource utilization, medication use and type of insulin. RESULTS: 13,296 patients were included in the BAS cohort (5,502 adherent; 7,794 nonadherent) and 10,069 in the BAS-BOL cohort (2,006 adherent; 8,063 nonadherent). Adherent patients had significantly lower all-cause total unadjusted costs following initiation on BAS ($29,322 vs. $31,888, P = 0.0134) and BAS-BOL combination ($36,229 vs. $40,147, P = 0.0078). Drug costs comprised 39.5%-45.4% of costs among adherent patients and 23.0%-25.9% of costs among nonadherent patients. Multivariable analyses revealed that adherent patients had significantly lower adjusted all-cause total costs than nonadherent patients in the BAS cohort ($30,127 vs. $37,049, 95% CI for difference −$8,460 to −$5,384) and the BAS-BOL cohort ($36,603 vs. $44,702, 95% CI for difference −$9,129 to −$6,980). CONCLUSIONS: In patients with T2D who initiated BAS or BAS-BOL combination therapy, adherence was associated with significantly lower all-cause total health care costs, despite significantly higher drug costs. These results illustrate the potential economic benefits associated with adherence to insulin therapy.