Predictors of adherence to insulin therapy in type 2 diabetes mellitus: an application of the theory of planned behavior

Abstract

Background: Non-adherence to medication therapy in type 2 diabetes mellitus (DM2) is prevalent. Theoretical models have been used to identify the proximal determinants of behavior. Aim: To identify the direct psychosocial predictors of adherence to insulin therapy based on Theory of Planned Behavior (TPB), among outpatients with DM2. Methods: Longitudinal and predictive study, whose data was collected at baseline and 3-month follow-up. At baseline (n = 119), sociodemographic and clinical data, self-reported measures of insulin adherence, psychosocial variables of TPB and glycated hemoglobin (A1C) were collected. At 3-month follow-up (n = 70), measurements of insulin adherence and A1C were again measured. Multiple linear regression, via generalized linear models and Multiple Poisson regression, with robust variance analysis were used, for quantitative and categorical outcomes, respectively. Results: One point in the Intention score led to a mean increase of 12.5% in the proportion of insulin doses, and there was a mean increase of 25% in the probability of the person taking insulin every day or practically every day. Attitude was a predictor of Intention. The moderation analysis demonstrated that higher levels of Perceived Behavioral Control weakened the effect of Attitude on Intention. Conclusions: The results showed that Intention was predictor of behavioral measure of adherence and the proportion of insulin doses. Attitude was predictor of Intention and Perceived Behavioral Control moderated the effect of Attitude and Subjective Norm on Intention. These findings highlight the importance of developing interventions that prioritize motivational strategies to enhance insulin adherence in the clinical practice. However, future studies with larger sample sizes and the inclusion of belief assessments are recommended to optimize the understanding of the psychosocial determinants of insulin adherence among outpatients with DM2.