Analysis of Factors Contributing to PT-INR Elevation during Antimicrobial Therapy in Patients Taking Warfarin

Abstract

It is common for the prothrombin time-internationally normalized ratio (PT-INR) to increase during antimicrobial therapy in patients taking warfarin. Antimicrobial agents that are likely to increase PT-INR include broad-spectrum agents and those that contain N-methylthiotetrazole side chains. In this study, we retrospectively examined the effects of the type of antimicrobial agent and the background of patients receiving antimicrobial agents on changes in the PT-INR. The subjects were patients who received antimicrobial agents while taking warfarin from 2013 to 2017. There were 33 patients in the group with elevated PT-INR and 35 patients in the group with nonelevated PT-INR. In the univariate analysis for the search for factors contributing to PT-INR elevation, there were significant differences in missed meals, pneumonia, and the total number of antibacterial agents used (p<0.05), but not in the type of antimicrobial agent. The results for PT-INR elevation factors were similar to those of the univariate analysis in the multivariate analysis. The odds ratios (95% confidence interval) were 5.33 (1.47-19.30) for missed meals, 4.17 (1.28-13.60) for pneumonia, and 3.53 (1.32-9.43) for the total number of antibacterial agents used, respectively. These results suggest that no specific type of antimicrobial agent is responsible for the increase in PT-INR; however, multiple factors may be involved in the increase in PT-INR during antimicrobial therapy.