Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Patients in intensive care unit are prescribed large numbers of drugs, highlighting the need to study potential Drug-Drug Interactions in this environment. The aim of this study was to delineate the prevalence and risk of potential drug-drug interactions between medications administered to patients in an ICU. This cross-sectional observational study was conducted during 12 months, in an adult ICU of a teaching hospital. Inclusion criteria were: prescriptions with 2 or more drugs of patients admitted to the ICU for > 24 hours and age of >= 18 years. Potential Drug-Drug Interactions were quantified and classified through Micromedex (TM) database. The 369 prescriptions included in this study had 205 different drugs, with an average of 13.04 +/- 4.26 ( mean +/- standard deviation) drugs per prescription. Potential Drug-Drug Interactions were identified in 89% of these, with an average of 5.00 +/- 5.06 interactions per prescription. Of the 405 different pairs of potentially interacting drugs identified, moderate and major interactions were present in 74% and 67% of prescriptions, respectively. The most prevalent interaction was between dipyrone and enoxaparin (35.8%), though its clinical occurrence was not observed in this study. The number of potential Drug-Drug Interactions showed significant positive correlations with the length of stay in the intensive care unit, and with the number of prescribed drugs. Acknowledging the high potential for Drug-Drug Interactions in the ICU represents an important step toward improving patient safety and best therapy results.531National Council of Technological and Scientific Development (CNPq. Brasilia, DF, Brazil)Sao Paulo Research Foundation (FAPESP. Sao Paulo, SP, Brazil)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)