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.
Keywords: antidiabetic medication; clusters of adherence; longitudinal trajectories; pharmacoepidemiology; type 2 diabetes.
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