Basal Insulin Adherence in Patients with Type 2 Diabetes Mellitus in Routine Clinical Practice in Spain: Clinical and Economic Impact

Type 2 diabetes mellitus (T2DM) imposes a clinical and economic burden, largely due to its long-term micro- and macrovascular complications. To prevent these complications, treatment adherence is essential. The aim of this study was to analyse basal insulin adherence and its clinical and economic repercussions in patients with T2DM in Spain. Retrospective, descriptive observational study using the Spanish Health Improvement Network (THIN®) database. Adult patients with T2DM, a registry entry of first basal insulin prescription from January 2014, and prescription/dispensation records between January 2014 and January 2024 were included. Adherence was estimated as proportion of days covered ≥ 80% in patients with ≥ 1 (full-population) and ≥ 3 years of follow-up (≥ 3 years subpopulation). Sociodemographic, clinical characteristics, micro- and macrovascular complications incidence, healthcare resource use (HCRU) (outpatient general practitioner/nursing/specialists visits and laboratory tests), and sick leave were analysed in adherent and non-adherent patients of the ≥ 3 years subpopulation. Direct (complications + HCRU) and indirect costs were calculated. A total of 9441 patients in the full-population and 4693 in the ≥ 3 years subpopulation were included. Less than 70% were adherent (66.90% and 69.51%, respectively). Although adherent patients tended to be older and more were retired, sociodemographic and clinical characteristics were consistent in adherent and non-adherent patients. In both groups, 17–20% had micro- and 30–40% had macrovascular complications, but non-adherent patients showed increases of 5.54% and 15.90% in annual complications. Mean annual costs for micro- and/or macrovascular complications were €1091.68 for adherent and €1306.45 for non-adherent patients. Mean annual direct and indirect costs were €1528.45 and €784.97 in adherent and €1651.39 and €952.89 in non-adherent patients. This study shows less than 70% adherence to basal insulin under routine clinical practice in Spain and reveals unmet needs in current T2DM therapies. Non-adherence could result in more complications, which would lead to higher costs for the healthcare system. Type 2 diabetes mellitus (T2DM) is a severe disease that can lead to serious long-term complications. Preventing these complications depends on patients taking their treatments as prescribed, referred to as treatment adherence. This descriptive observational study analysed healthcare data from a Spanish database to assess adherence to basal insulin in adults with type 2 diabetes and to evaluate its impact on health outcomes and costs. With this purpose, prescription/dispensation records between January 2014 and January 2024 were analysed. Adherence was defined as dispensing records covering at least 80% of the prescribed basal insulin, assessed over at least 1 and 3 years of follow-up. Less than 70% of patients were adherent. Adherent and non-adherent patients had similar clinical characteristics, but patients who did not follow their treatment had an increase in annual complications affecting blood vessels. In adherent and non-adherent patients, mean annual costs for diabetes complications ranged from approximately €1100 to €1300, with direct and indirect costs between approximately €780 and €1650. These findings show that suboptimal adherence to basal insulin is common in routine clinical practice in Spain and this adds to the costs of treatment, imposing strain on the health system.