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Ann Pharmacother. 2014 May;48(5):562-70. doi: 10.1177/1060028014526362. Epub 2014 Feb 28.

Longitudinal effects of medication nonadherence on glycemic control.

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Ralph H. Johnson Veterans Affairs Medical Center, Charleston, SC, USA.



Medication nonadherence is known to worsen glycemic control. Few studies have examined this relationship over several years.


The aim of this study was to examine the longitudinal effect of medication nonadherence on glycemic control among a large cohort of veterans.


Analysis was performed on a cohort of 11 272 veterans with type 2 diabetes followed from April 1994 to May 2006. The primary outcome measures were mean glycosylated hemoglobin A1c (A1C) and proportion in poor control (A1C > 8%) over time. The main predictor was medication nonadherence based on medication possession ratio (MPR). Other covariates included sociodemographics and ICD-9 coded medical and psychiatric comorbidities. Generalized linear mixed models (GLMMs) were used to assess the relationship between MPR and A1C after adjusting for covariates.


Mean follow-up was 5.4 years. In the linear mixed model, after adjusting for baseline A1C and other confounding variables, mean A1C decreased by 0.24 (P < 0.001) for each 10% increase in MPR (95% CI = -0.27, -0.21). In the fully adjusted GLMM, each percentage increase in MPR was associated with a 48% lower likelihood of having poor glycemic control (odds ratio = 0.52; 95% CI = 0.4, 0.6). In both continuous and dichotomized A1C analyses, average A1C showed a decreasing trend over the study period (P < 0.001).


In patients with type 2 diabetes, glycemic control worsens over time in the presence of medication nonadherence. Future studies need to take into account the complexity of patient- and system-level factors affecting long-term medication adherence to improve diabetes-related outcomes.


databases; epidemiology; outcomes research/analysis; type 2 diabetes

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