title: The impact of number of drugs prescribed on the risk of potentially inappropriate medication among outpatient older adults with chronic diseases.
abstract: BACKGROUND
  Older patients with chronic diseases often take multiple prescription drugs, increasing their risk of adverse health events. However, polypharmacy remains ill-defined.
  
  
  OBJECTIVE
  To investigate the impact of number of drugs prescribed on potentially inappropriate medication (PIM) and the associated risk factors in older outpatients with chronic diseases.
  
  
  METHODS
  Retrospective cross-sectional study.
  
  
  METHODS
  We retrospectively assessed 780 older patients (mean, 75.5 ± 7.1 years) with long-term (≥ 28 days) prescriptions for chronic diseases at the geriatric clinics of a university hospital from January to June 2012 using the Screening Tool of Older Person's potentially inappropriate Prescriptions (STOPP). Clinical information for each patient was analyzed. Logistic regression and receiver operating characteristic curve (ROC) analyses were performed; number needed to harm (NNH) was also estimated.
  
  
  RESULTS
  According to STOPP criteria, 302 patients (39%) had at least one PIM. Multivariate analysis revealed that PIM risk was associated with the number of medications prescribed (P < 0.001) and the presence of cardiovascular (P < 0.001) or gastrointestinal disease (P = 0.003). The estimated area under the ROC for the number of medications needed to predict PIM risk was 0.680 (P < 0.001) with the optimal cut-off value of five medications. After adjusting covariates, patients prescribed ≥ 5 drugs [adjusted odds ratio (OR) = 5.4; adjusted NNH = 4.25; P < 0.001] and those prescribed 4 drugs (adjusted OR = 3.5; adjusted NNH = 6.88; P = 0.003) had significantly higher PIM risk than those prescribed ≤ 2 drugs.
  
  
  CONCLUSIONS
  The number of prescribed medications can be an index of PIM risk in older patients with chronic diseases. Clinicians should suspect high PIM risk in older outpatients with ≥ 5 prescriptions.
authors.affiliation: Faculty of Medicine, Institute of Medicine and School of Medicine, Chung Shan Medical University, No. 110, Sec. 1, Jianguo N. Rd., Taichung 40201, Taiwan. sccy399@yahoo.com.tw.
authors.forename: M-C
authors.initials: MC
authors.lastname: Weng
authors.forename: C-F
authors.initials: CF
authors.lastname: Tsai
authors.forename: K-L
authors.initials: KL
authors.lastname: Sheu
authors.forename: Y-T
authors.initials: YT
authors.lastname: Lee
authors.forename: H-C
authors.initials: HC
authors.lastname: Lee
authors.forename: S-L
authors.initials: SL
authors.lastname: Tzeng
authors.forename: K-C
authors.initials: KC
authors.lastname: Ueng
authors.forename: C-C
authors.initials: CC
authors.lastname: Chen
authors.forename: S-C
authors.initials: SC
authors.lastname: Chen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002908:Chronic Disease / Q000188:drug therapy*; D015897:Comorbidity; D003430:Cross-Sectional Studies; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D006801:Humans; D057970:Inappropriate Prescribing / Q000009:adverse effects* / Q000517:prevention & control / Q000706:statistics & numerical data*; D016015:Logistic Models; D008297:Male; D008508:Medication Errors / Q000517:prevention & control; D016017:Odds Ratio; D010045:Outpatients; D019338:Polypharmacy; D012372:ROC Curve; D012189:Retrospective Studies; D012307:Risk Factors; D013624:Taiwan / Q000453:epidemiology