Potenciais interações medicamentosas em prescrições de um hospital-escola de Porto Alegre Potential drug interactions among prescriptions of a teaching hospital in Porto Alegre

Introduction: Reports of the prevalence of drug interactions in Brazilian hospitals are scarce. Aims: To describe the prevalence of potential drug interactions among the medical drugs prescribed in the clinical and surgical units of a teaching hospital. Secondarily, to describe the characteristics of drug interactions and relate their occurrence to the number of prescribed medications and patient age. Patients and Methods: The data were collected from Monday to Friday of a week in Oct 2007, starting from the last prescription form found in the medical charts, and involved 128 prescription forms with 10.5±4.1 drugs. The patients’ mean age was 58.6±16.9 years and 51.2% were males. Cardiovascular disease was the main disease (23.4%) and the most frequently found comorbidity (42.5%). The analysis of interactions was done through consultation with an interactive system (Micromedex ® ). Results: 485 cases of drug interactions were found, being present in 79.7% (CI95%: 72.686.8) of the prescription forms (mean 3.8). The most frequent interaction was captopril/dipyrone (9.7%), followed by dipyrone/furosemide (4,5%), and the most frequently involved drugs were dipyrone (29.3%) and captopril (21.2%). Most of the interactions had a pharmacodynamic mechanism (65.5%), moderate severity (55.5%), late onset (61.3%), and a good scientific basis (71.1%). The prevalence of interactions was strongly associated with the number of drugs prescribed (r=0.65, p<0.001) and weakly associated with patient age.