The impact of number of drugs prescribed on the risk of potentially inappropriate medication among outpatient older adults with chronic diseases

QJM. 2013 Nov;106(11):1009-15. doi: 10.1093/qjmed/hct141. Epub 2013 Jul 8.


Background: Older patients with chronic diseases often take multiple prescription drugs, increasing their risk of adverse health events. However, polypharmacy remains ill-defined.

Aim: 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.

Design: 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.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Chronic Disease / drug therapy*
  • Comorbidity
  • Cross-Sectional Studies
  • Dose-Response Relationship, Drug
  • Drug Interactions
  • Female
  • Humans
  • Inappropriate Prescribing / adverse effects*
  • Inappropriate Prescribing / prevention & control
  • Inappropriate Prescribing / statistics & numerical data*
  • Logistic Models
  • Male
  • Medication Errors / prevention & control
  • Odds Ratio
  • Outpatients
  • Polypharmacy*
  • ROC Curve
  • Retrospective Studies
  • Risk Factors
  • Taiwan / epidemiology