Study of warfarin utilization in hospitalized patients: analysis of possible drug interactions.

Background Drug-drug interactions in patients taking warfarin may contribute to a higher risk of adverse events. Objective To identify and evaluate the prevalence and characteristics of potential DDIs with warfarin. Methods A cross-sectional study was performed in a Brazilian tertiary hospital. The electronic prescriptions of the patients receiving warfarin between January 2004 and December 2010 were analyzed. Socio-demographic, clinical, and therapeutic variables were collected. Warfarin drug-drug interactions were classified as either risk A, B, C, D, or X according to the Lexi-Interact™ Online database. Results A total of 3048 patients were identified who were prescribed warfarin. Of the 154,161 total drug prescriptions issued, 42,120 (27.3 %) were for warfarin. Evaluation of the prescriptions showed that 63.1 and 0.1 % of patients received concomitant drugs classified as having class D or X risk. It was found that 20,539 (48.7 %) prescriptions had at least one drug with a D or X risk. Patients were prescribed an average of 1.4 (±0.4) concomitant medications with a class D or X warfarin-DDI risk, the most frequent being acetylsalicylic acid and amiodarone. Conclusion The results demonstrate a high prevalence of concomitant drug prescriptions with the potential for clinically relevant DDIs with warfarin, the most frequent being acetylsalicylic acid and amiodarone.