title: Adherence to Oral Glucose-Lowering Therapies and Associations With 1-Year HbA1c: A Retrospective Cohort Analysis in a Large Primary Care Database.
abstract: OBJECTIVE
  The impact of taking oral glucose-lowering medicines intermittently, rather than as recommended, is unclear. We conducted a retrospective cohort study using community-acquired U.K. clinical data (Clinical Practice Research Database [CPRD] and GoDARTS database) to examine the prevalence of nonadherence to treatment for type 2 diabetes and investigate its potential impact on HbA1c reduction stratified by type of glucose-lowering medication.
  
  
  METHODS
  Data were extracted for patients treated between 2004 and 2014 who were newly prescribed metformin, sulfonylurea, thiazolidinedione, or dipeptidyl peptidase 4 inhibitors and who continued to obtain prescriptions over 1 year. Cohorts were defined by prescribed medication type, and good adherence was defined as a medication possession ratio ≥0.8. Linear regression was used to determine potential associations between adherence and 1-year baseline-adjusted HbA1c reduction.
  
  
  RESULTS
  In CPRD and GoDARTS, 13% and 15% of patients, respectively, were nonadherent. Proportions of nonadherent patients varied by the oral glucose-lowering treatment prescribed (range 8.6% [thiazolidinedione] to 18.8% [metformin]). Nonadherent, compared with adherent, patients had a smaller HbA1c reduction (0.4% [4.4 mmol/mol] and 0.46% [5.0 mmol/mol] for CPRD and GoDARTs, respectively). Difference in HbA1c response for adherent compared with nonadherent patients varied by drug (range 0.38% [4.1 mmol/mol] to 0.75% [8.2 mmol/mol] lower in adherent group). Decreasing levels of adherence were consistently associated with a smaller reduction in HbA1c.
  
  
  CONCLUSIONS
  Reduced medication adherence for commonly used glucose-lowering therapies among patients persisting with treatment is associated with smaller HbA1c reductions compared with those taking treatment as recommended. Differences observed in HbA1c responses to glucose-lowering treatments may be explained in part by their intermittent use.
authors.affiliation: Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, United Kingdom.|Diabetes Trials Unit, University of Oxford, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Farmer
authors.affiliation: Institute of Health Research, University of Exeter Medical School, Exeter, UK.
authors.forename: Lauren R
authors.initials: LR
authors.lastname: Rodgers
authors.affiliation: Medical Research Institute, University of Dundee, Dundee, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Lonergan
authors.affiliation: NIHR Exeter Clinical Research Facility, University of Exeter Medical School, Exeter, UK.
authors.forename: Beverley
authors.initials: B
authors.lastname: Shields
authors.affiliation: Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, UK.
authors.forename: Michael N
authors.initials: MN
authors.lastname: Weedon
authors.affiliation: Medical Research Institute, University of Dundee, Dundee, UK.
authors.forename: Louise
authors.initials: L
authors.lastname: Donnelly
authors.affiliation: Diabetes Trials Unit, University of Oxford, United Kingdom.
authors.forename: Rury R
authors.initials: RR
authors.lastname: Holman
authors.affiliation: Medical Research Institute, University of Dundee, Dundee, UK.
authors.forename: Ewan R
authors.initials: ER
authors.lastname: Pearson
authors.affiliation: Department of Diabetes and Endocrinology, Royal Devon and Exeter NHS Foundation Trust, Exeter, UK.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Hattersley
mesh_terms: D000368:Aged; D001786:Blood Glucose / Q000187:drug effects; D015331:Cohort Studies; D016208:Databases, Factual; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000188:drug therapy*; D054873:Dipeptidyl-Peptidase IV Inhibitors / Q000627:therapeutic use; D005260:Female; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D008297:Male; D055118:Medication Adherence; D008687:Metformin / Q000627:therapeutic use; D008875:Middle Aged; D011320:Primary Health Care / Q000706:statistics & numerical data; D012189:Retrospective Studies; D013453:Sulfonylurea Compounds / Q000627:therapeutic use; D045162:Thiazolidinediones / Q000627:therapeutic use
chemical_list: D001786:Blood Glucose; D054873:Dipeptidyl-Peptidase IV Inhibitors; D006442:Glycated Hemoglobin; D007004:Hypoglycemic Agents; D008687:Metformin; D013453:Sulfonylurea Compounds; D045162:Thiazolidinediones; C089946:2,4-thiazolidinedione