title: Prevalence and determinants of unintended double medication of antihypertensive, lipid-lowering, and hypoglycemic drugs in Austria: a nationwide cohort study.
abstract: OBJECTIVE
  Double medication is defined as the unintended overlapping prescription of two identical substances with the same route of administration by two different prescribers to the same patient. Consequences of double medication are reduced patient safety and excess healthcare costs. Based on nationwide prescription data from 2011 covering 97% of Austria's population, we estimated double medication prevalences for treatment of hypertension, hyperlipidemia, and diabetes mellitus.
  
  
  METHODS
  We investigated prescriptions of 88 antihypertensive, 16 lipid-lowering and 29 hypoglycemic substances in 7,971,323 persons in 2011. Prevalence of double medication was calculated patientwise (prevalence by patients) and timewise (prevalence by patient-years). Risk factors for double medication were identified by logistic regression.
  
  
  RESULTS
  For antihypertensive, lipid-lowering, and hypoglycemic subtances, overall 15.0% (men: 15.1%, women: 15.0%), 13.1% (13.7%, 12.5%), and 13.0% (13.0%, 13.4%) of patients were doubly medicated, respectively. Corresponding prevalences by patient-years were 1.6%, 2.0%, and 1.2%. Logistic regression confirmed lower age and copayment waiver as independent risk factors of double medication. Furthermore, double medication occurred more often with prescriptions from hospitals or internal medicine specialists compared with general practitioners, as well as in August compared with earlier or later in the calendar year.
  
  
  CONCLUSIONS
  While appropriate care or comanagement of patients by internal medicine specialists and general practitioners may explain some of the double prescriptions, our data indicate that unintended double medication is frequent. In Austria, lack of financial incentives of patients to avoid filling duplicate prescriptions explains a considerable fraction of double medication occurrences.
authors.affiliation: Section for Clinical Biometrics, Center for Medical Statistics, Informatics and Intelligent Systems, Medical University of Vienna, Vienna, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Heinze
authors.affiliation: Section for Clinical Biometrics, Center for Medical Statistics, Informatics and Intelligent Systems, Medical University of Vienna, Vienna, Austria.
authors.forename: Lisanne M
authors.initials: LM
authors.lastname: Jandeck
authors.affiliation: Section for Clinical Biometrics, Center for Medical Statistics, Informatics and Intelligent Systems, Medical University of Vienna, Vienna, Austria.
authors.forename: Milan
authors.initials: M
authors.lastname: Hronsky
authors.affiliation: Sickness Fund Burgenland, Burgenländische Gebietskrankenkasse, Eisenstadt, Austria.
authors.forename: Berthold
authors.initials: B
authors.lastname: Reichardt
authors.affiliation: Austrian Agency for Health and Food Safety, Vienna, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Baumgärtel
authors.affiliation: Main Association of the Austrian Social Security Institutions, Vienna, Austria.|Department of Finance, University of Vienna, Vienna, Austria.
authors.forename: Anna
authors.initials: A
authors.lastname: Bucsics
authors.affiliation: Austrian Agency for Health and Food Safety, Vienna, Austria.|PERI Change GmbH, Vienna, Austria.
authors.forename: Marcus
authors.initials: M
authors.lastname: Müllner
authors.affiliation: Division of Nephrology, Stanford University School of Medicine, Palo Alto, CA, USA.|Section of Nephrology, Department of Medicine, Baylor College of Medicine, Houston, TX, USA.
authors.forename: Wolfgang C
authors.initials: WC
authors.lastname: Winkelmayer
mesh_terms: D000959:Antihypertensive Agents / Q000008:administration & dosage / Q000191:economics / Q000627:therapeutic use*; D001317:Austria / Q000453:epidemiology; D015331:Cohort Studies; D003920:Diabetes Mellitus / Q000188:drug therapy / Q000453:epidemiology; D016527:Drug Costs / Q000706:statistics & numerical data; D011307:Drug Prescriptions / Q000706:statistics & numerical data*; D006801:Humans; D006949:Hyperlipidemias / Q000188:drug therapy / Q000453:epidemiology; D006973:Hypertension / Q000188:drug therapy / Q000453:epidemiology; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000191:economics / Q000627:therapeutic use*; D000960:Hypolipidemic Agents / Q000008:administration & dosage / Q000191:economics / Q000627:therapeutic use*; D057970:Inappropriate Prescribing / Q000517:prevention & control / Q000706:statistics & numerical data*; D061214:Patient Safety; D015995:Prevalence
chemical_list: D000959:Antihypertensive Agents; D007004:Hypoglycemic Agents; D000960:Hypolipidemic Agents
keywords: anatomical therapeutic chemical (ATC) classification system; diabetes mellitus; drug utilization; duplicate prescription; hyperlipidemia; hypertension; pharmacoepidemiology