Background: Older patients with chronic diseases often take multiple prescription drugs, increasing their risk of adverse health events. However, poly-pharmacy 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 outpa-tients with chronic diseases. Design: Retrospective cross-sectional study. Methods: We retrospectively assessed 780 older pa-tients (mean, 75.5 AE 7.1 years) with long-term (528 days) prescriptions for chronic diseases at the geri-atric 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 gastro-intestinal 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 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 42 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 55 prescriptions.
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