Potential Drug-Drug Interactions Associated with Prolonged Stays in the Intensive Care Unit A Retrospective Cohort Study

Background and Objectives: Drug-drug interactions (DDIs) are one cause of adverse drug events and can cause harm to hospitalized patients. Little has been done to study the relationship between potential DDIs and an increased length of stay (LOS) in the intensive care unit (ICU). The aim of this study was to determine the frequency of potential DDIs during ICU stays and to determine whether the frequency of these adverse events was associated with ICU LOS. Methods: This retrospective cohort study was conducted from January to December 2007 in the ICU of the General Hospital of Vitoria da Conquista, Brazil. The study population comprised all patients aged > 18 years admitted to the hospital's ICU. Demographic and prescription data were collected from medical files. All prescriptions administered during the period were examined. Potential DDIs were identified and classified according to the book Drug Interaction Facts. The median LOS was determined by the Kaplan-Meier method and Cox proportional hazards models were fitted to analyse the relationship between potential DDIs and the LOS. Results: The study population comprised 236 adults, 158 (67%) of them men, between the ages of 18 and 96 years, with a mean +/- SD age of 50 +/- 20 years. The median LOS among patients with at least one DDI was 12 days compared with 5 days among those with no DDIs (p < 0.01). Multiple Cox proportional regression analyses showed that a prolonged ICU stay was positively associated with DDIs (hazard ratio [HR] 0.54; 95% CI 0.37, 0.80; p < 0.01), where an HR < 1 indicates a variable that increases the risk of prolonged stay (i.e. an adverse outcome). This association was true even after controlling for the cost of hospitalization, the number of procedures and the number of prescribed drugs. Conclusion: In this study, DDIs were found to be associated with a longer ICU stay. Given that LOS is an important indicator of the quality of health care delivered and that DDIs are considered avoidable, specific measures are necessary to increase the recognition of DDIs. E-prescriptions and dispensing programmes associated with a DDI knowledge base can help health professionals identify hazardous drug combinations.