Evaluation of the Effect of Apixaban on INR in the Inpatient Population

Direct oral anticoagulants (DOACs), particularly direct factor Xa inhibitors, have been associated with prolongation of the prothrombin time and the international normalized ratio (INR). Although DOACs do not require monitoring, elevations in the INR have been reported in in vitro and observational studies. The literature surrounding the extent of elevation and the clinical significance is limited. The objective of this study was to quantify the degree of INR elevation in hospitalized patients receiving apixaban. This was a single-center, retrospective, observational analysis of adult patients who received at least 1 dose of apixaban during their hospital admission and had at least 1 INR sample collected prior to and following administration. The major end point of this study was to characterize the effect of apixaban on the INR by determining the percentage of patients with an INR higher than our laboratory defined normal (defined as INR > 1.1). Minor end point outcomes included the incidence of an INR increase >0.3 from baseline INR and additional patient-specific factors that may influence INR elevation. Seventy-nine patients were included in the analysis. On day 1 of therapy, the median (interquartile range, IQR) INR was 1.4 (1.3:1.6) with 84.5% of patients having an elevated INR. The median (IQR) INR increased to 1.5 (1.4:1.6) and 1.7 (1.5:1.9) on day 4 and day 7, respectively. Of patients whose INR increased by more than 0.3, the median (IQR) change in INR from baseline was 0.5 (0.4:0.6). Apixaban is associated with a notable increase in INR in hospitalized patients, although it is not clear the clinical impact of the increase. Although literature does not support monitoring INR as a marker of apixaban activity, it is important for clinicians to understand the association apixaban has on the INR to avoid inappropriate interpretation of routine coagulation assays.