title: Impact of hospitalization on medication adherence estimation in claims data.
abstract: OBJECTIVE
  Pharmacy claims are commonly used to assess medication adherence. It is unclear how different approaches to handling hospitalizations compare to the gold standard of using outpatient and inpatient drug data. This study aimed to compare the impact of different approaches to handling hospitalizations on medication adherence estimation in administrative claims data.
  
  
  METHODS
  We identified β-blocker initiators after myocardial infarction (MI) and statin initiators regardless of hospitalization histories in the population-based, Taiwan database, which includes outpatient and inpatient drug claims data. Adherence to β-blockers or to statins during a 365-day follow-up period was estimated in outpatient pharmacy claims using the proportion of days covered (PDC) in three ways: ignoring hospitalizations (PDC1); subtracting hospitalized days from the denominator (PDC2); and assuming drug use on all hospitalized days (PDC3). We compared these to an approach that incorporated inpatient drug use (PDC4). We also used a hypothetical example to examine variations across approaches in several scenarios, such as increasing hospitalized days.
  
  
  CONCLUSIONS
  Mean 365-day PDC was 74% among 1729 post-MI β-blocker initiators (range: 73.1%-74.9%) and 44% among 69 435 statins initiators (range: 43.5%-44.0%), which varied little across approaches. Differences across approaches increased with increasing number of hospitalized days. For patients hospitalized for >28 days, mean difference across approaches was >15%. PDC3 consistently yielded the highest value and PDC1 the lowest.
  
  
  CONCLUSIONS
  On average, different approaches to handling hospitalizations lead to similar adherence estimates to the gold standard of incorporating inpatient drug use. When patients have many hospitalization days during follow-up, the choice of approach should be tailored to the specific setting.
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.|Faculty of Pharmacy, School of Pharmaceutical Science, National Yang-Ming University, Taipei, Taiwan.|Center of Comparative Effectiveness Research, National Center of Excellence for Clinical Trial and Research, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Dong
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: N K
authors.initials: NK
authors.lastname: Choudhry
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: A
authors.initials: A
authors.lastname: Krumme
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Lee
authors.affiliation: Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: L-C
authors.initials: LC
authors.lastname: Wu
authors.affiliation: Center of Comparative Effectiveness Research, National Center of Excellence for Clinical Trial and Research, National Taiwan University Hospital, Taipei, Taiwan.|Graduate Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan.
authors.forename: M-S
authors.initials: MS
authors.lastname: Lai
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Gagne
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage* / Q000627:therapeutic use; D000368:Aged; D016208:Databases, Factual / Q000706:statistics & numerical data; D005260:Female; D005500:Follow-Up Studies; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000008:administration & dosage* / Q000627:therapeutic use; D007297:Inpatients / Q000706:statistics & numerical data; D007356:Insurance, Pharmaceutical Services / Q000706:statistics & numerical data; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000188:drug therapy; D010045:Outpatients / Q000706:statistics & numerical data; D013624:Taiwan; D016903:Drug Monitoring
chemical_list: D000319:Adrenergic beta-Antagonists; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors
keywords: adherence measures; hospitalizations; proportion of days covered; statins; β-blockers