Non-adherence to non-insulin glucose-lowering drugs: Prevalence, predictors and impact on glycemic control and insulin initiation. A longitudinal cohort study in a large primary care database in Spain.

Background: A better understanding of patient non-adherence to type 2 diabetes medication is needed to design effective interventions to address this issue.

Objectives: (1) To estimate the prevalence of non-adherence to diabetes medication; (2) to examine its impact on glycemic control and insulin initiation; (3) to develop and validate a prediction model of non-adherence.

Methods: We conducted a longitudinal cohort study based on data from electronic health records. We included adult patients registered within the Health Service of the Balearic Islands (Spain) starting a new prescription of a non-insulin glucose-lowering drug between January 2016 and December 2018. We calculated non-adherence at 12 months follow-up, defined as medication possession ratio (MPR) ≤ 80%. We fitted multivariable regression models to examine the association between non-adherence and glycemic control and insulin initiation and identified predictors of non-adherence.

Results: Of 18,119 patients identified, after 12 months follow-up, 5,740 (31.68%) were non-adherent. Compared with non-adherent, adherent patients presented lower HbA1c levels (mean difference = -0.32%; 95%CI = -0.38%; -0.27%) and were less likely to initiate insulin (aOR = 0.77; 95%CI = 0.63; 0.94). A predictive model explained 22.3% of the variation and presented a satisfactory performance (AUC = 0.721; Brier score = 0.177). The most important predictors of non-adherence were: non-Spanish nationality, currently working, low adherence to previous drugs, taking biguanides, smoker and absence of hypertension.

Conclusion: Around one-third of the patients do not adhere to their non-insulin glucose-lowering drugs. More research is needed to optimise the performance of the predicting model before considering its implementation in routine clinical practice.