Longitudinal Trajectories of Antidiabetic Medication Adherence Over 5 Years From Treatment Initiation—A Swedish Nationwide Cohort Study

Patients' longitudinal adherence to antidiabetic medication in routine clinical care remains unexplored. This study aimed to identify adherence groups among individuals with type 2 diabetes with up to 1 and 5 years of follow-up. This was a register-based cohort study using data from Swedish national health and population registers and the National Diabetes Register (2006-2022). New users of blood glucose-lowering drugs (other than insulin) were identified. Trajectories of the proportion of days covered (PDC) by any antidiabetic medication, including insulin, over 1- and 5-year periods were clustered using k-means for longitudinal data. Analyses up to 1- and 5-year follow-up periods included 75,421 individuals with an overall mean PDC of 0.7 and 283,795 individuals with an overall mean PDC of 0.3, respectively. K-means clustering identified two main adherence groups. For the 1-year follow-up, 70.6% of individuals were in the cluster with a higher mean PDC (0.9) and 29.4% in the cluster with a lower mean PDC (0.4). The corresponding figures for the 5-year follow-up were 36.9% (higher mean PDC [0.9]) and 63.1% (lower mean PDC [0.3]). Clusters with higher mean trajectories of PDC included more men, older individuals, patients using drugs from only one antidiabetic medication class, and noninsulin users during follow-up. Mean trajectories of adherence decreased mainly during the first year. This study identified a substantial problem with longitudinal adherence to any antidiabetic medication, with a low proportion of individuals clustered as having higher adherence during the 5-year follow-up. Results suggest the need for interventions via follow-up strategies aiming at monitoring and improving continuous treatment management while considering tailored treatment strategies.