Concordance rate amongst electronic databases regarded the information on potential drug interactions between warfarin and antimicrobials: a descriptive analysis

Abstract Background: Although not always avoidable, drug-drug interaction (DDI) is an example of a predictable adverse event. Warfarin is a narrow therapeutic window oral anticoagulant that has been described to interact with antimicrobials (AM), affecting therapy efficacy and/or safety of anticoagulant and/or antimicrobial treatment. Aim: To evaluate the intrarater agreement on information about potential DDI between warfarin and AM present in the Municipal Essential Medicines List of Porto Alegre (REMUME/POA), Rio Grande do Sul, Brazil, between different electronic databases (EDB). Method: This descriptive analysis evaluated the EDB UpToDate®, Drugs.com®, Medscape®, and Micromedex® on information about DDI mechanism, severity classification, and clinical management. Results: Amongst the 20 AM listed, 17 had a potential DDI with warfarin described in at least one EDB. Total agreement rate between EDB regarding classification of DDI was 30%; as for partial concordance, rates among 2 and 3 EDB were respectively 25% and 45%. Most concordant EDB were UpToDate® and Drugs.com® (85%). For mechanism of DDI, the overall concordance rate was 12%; partial agreement was 35% and 23.5% on two and three EDB, respectively. Overall agreement rate for clinical management of DDI was 18%; partial agreement between 2 and 3 EDB was 29% and 53%, respectively. Conclusion: Overall concordance rate is relatively low, considering the information obtained for the three aspects evaluated. The partial concordance rate, however, is higher, reaching 45% of the drugs with concordant DDI classification for three out of four EDB. Further studies are needed to evaluate the robustness of the evidence employed by EDB.