title: Longitudinal effects of medication nonadherence on glycemic control.
abstract: BACKGROUND
  Medication nonadherence is known to worsen glycemic control. Few studies have examined this relationship over several years.
  
  
  OBJECTIVE
  The aim of this study was to examine the longitudinal effect of medication nonadherence on glycemic control among a large cohort of veterans.
  
  
  METHODS
  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.
  
  
  RESULTS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Ralph H. Johnson Veterans Affairs Medical Center, Charleston, SC, USA.
authors.forename: Leonard E
authors.initials: LE
authors.lastname: Egede
authors.forename: Mulugeta
authors.initials: M
authors.lastname: Gebregziabher
authors.forename: Carrae
authors.initials: C
authors.lastname: Echols
authors.forename: Cheryl P
authors.initials: CP
authors.lastname: Lynch
mesh_terms: D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy*; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D014728:Veterans; D016903:Drug Monitoring
chemical_list: D006442:Glycated Hemoglobin; D007004:Hypoglycemic Agents
keywords: databases; epidemiology; outcomes research/analysis; type 2 diabetes