Agreement among four drug information sources for the occurrence of warfarin drug interactions in Brazilian heart disease patients with a high prevalence of Trypanosoma cruzi infection.

PURPOSE: The aim of this study was to assess the agreement of four renowned interaction lists on potentially severe warfarin drug interactions (DI) in outpatients at a university hospital in Brazil, specifically in subgroups of Trypanosoma cruzi-infected and non-infected patients and those with previous bleeding episodes. METHODS: This was a cross-sectional study in which adult outpatients with heart disease and indications for chronic warfarin use were enrolled. The occurrence of potentially severe warfarin DI was evaluated based on the lists provided by three compendia, i.e., Drug Interaction Facts (DIF), Drug Interactions: Analysis and Management (DIAM) and DRUG-REAX, and by the World Health Organization (WHO) Model Formulary. A kappa coefficient was used to calculate the agreement among the sources. RESULTS: A total of 280 patients were studied. Most patients were female (54.6 %) with an average age of 56.8 (standard deviation 13.1) years. The agreement among the four sources was fair (Fleiss' kappa coefficient = 0.295). T. cruzi-infected individuals were less likely to have severe warfarin DI than non-infected patients (p < 0.05 for DIAM, DRUG-REAX and the WHO Model Formulary). Potentially severe DI were more frequent in patients with previous bleeding episodes, based on the DIF compendia (p = 0.007). CONCLUSIONS: This evaluation of warfarin DI revealed that the disagreement between compendia is also observed in clinical practice. T. cruzi infection is associated with a lower prevalence of potentially severe warfarin DI, but with a wider variation in its detection. Our results suggest a wide spectrum of discrepancies in detecting heart disease patients at higher risk for severe warfarin DI and a possible heterogeneity in clinical guidance.

Warfarin drug interactions: a comparative evaluation of the lists provided by five information sources.

PURPOSE: Detecting potential drug interactions can lead to early interventions that protect patients from serious drug-related problems. The aim of this study was to evaluate the agreement among the lists of warfarin interactions provided by five information sources. METHODS: The lists of warfarin interactions and the corresponding severity ratings and documentation levels presented by the three compendia and by the World Health Organization (WHO) Model Formulary were all compared, and each list was compared to that provided on the package insert of Marevan, a brand of warfarin. The compendia used were: Drug Interaction Facts, Drug Interactions: Analysis and Management and DRUG-REAX. A kappa coefficient was used to calculate the agreement among the sources. RESULTS: A total of 537 interactions were listed. Only 13 (2.4%) were common to the five sources. The global Fleiss' kappa coefficient was -0.0080, which indicated poor agreement. Eleven warfarin interactions appeared only in the Marevan package insert. Importantly, 243 interactions (45.3% of the total) were deemed significant in at least one compendium. Only two warfarin interactions were reported as critical by all three compendia and by WHO. The most critical interactions cited by the compendia were missing from the package insert. CONCLUSIONS: Poor agreement was found among five sources listing warfarin interactions. Potentially severe clinical consequences might occur due to these discrepant recommendations. Finally, the lack of standard terminology and clinical guidance, as well as the possible inaccuracy of severity ratings and documentation might contribute to heterogeneous procedures in clinical practice.