Objective: Medical professionals are often challenged by lack of patient compliance with pharmaceutical treatments. Research has shown that patients with diabetes have one of the lowest medication adherence rates at 65% to 85%. Some causes have been identified in the literature, but the influence of type of medication is unknown. This study assessed the impact of a broad range of factors on medication adherence and persistence among adult patients with type 2 diabetes mellitus.

Methods: Patients were selected from the Truven Health MarketScan Research Databases of healthcare administrative claims (2009 through 2012), assigned to mutually exclusive cohorts based on initiation of saxagliptin (a dipeptidyl peptidase-4 [DPP-4] inhibitor), or a glucagon-like peptide 1 (GLP-1) receptor agonist (daily or twice daily formulation), sulfonylurea (SU), or thiazolidinedione (TZD), and screened for continuous enrollment 1 year before and after drug initiation. Adherence and persistence were measured using proportion of days covered and time to discontinuation, respectively. Multivariate models were used to examine the impact of study drug and demographic and clinical factors.

Results: Overall, 45.1% of patients were adherent with their study drug over the 1 year follow-up period. Adherence was higher among patients who were male, older, or residing in non-Southern states. Adherence was better with mail-order use and lower levels of cost sharing. Patients taking a GLP-1 (OR = 0.40, 95% CI = 0.37, 0.42), SU (OR = 0.49, 95% CI = 0.46, 0.52), or TZD (OR = 0.54, 95% CI = 0.51, 0.57) were less likely to be adherent compared with those taking saxagliptin. Results were mixed regarding the impact of comorbidities and polypharmacy on medication adherence. Influencing factors may be the type of comorbidity, overall health level, number of drugs, and complexity of the drug regimen.

Key limitations: Adherence was measured using data for prescriptions dispensed and it is not known whether patients actually took the medications, hence adherence may be overestimated. Whether patients who discontinued the study drugs switched to other diabetes medications or discontinued treatment completely was not measured.

Conclusion: Identified risk factors can guide medical professionals in their attempts to increase the likelihood of patient adherence to drug treatment regimens.