Therapeutic monitoring of rivaroxaban in dogs using thromboelastography and prothrombin time

Abstract Background The chromogenic anti‐Xa assay, the gold standard for monitoring the anti‐Xa effect of rivaroxaban, is not available as a cage‐side diagnostic test for use in a clinical setting. Hypothesis/Objectives To evaluate clinical modalities for measuring the anticoagulant effects of rivaroxaban using a point‐of‐care prothrombin time (PT) and thromboelastography (TEG). Animals Six healthy Beagle dogs. Methods Prospective, experimental study. Four different doses of rivaroxaban (0.5, 1, 2, and 4 mg/kg) were administered PO to dogs. Single PO and 3 consecutive dosing regimens also were assessed. Plasma rivaroxaban concentration was determined using a chromogenic anti‐Xa assay, point‐of‐care PT, and TEG analysis with 4 activators (RapidTEG, 1 : 100 tissue factor [TF100], 1 : 3700 tissue factor [TF3700], and kaolin), and results were compared. Spearman correlation coefficients were calculated between ratios (peak to baseline PT; peak reaction time [R] of TEG to baseline [R] of TEG) and anti‐Xa concentration. Results Anti‐Xa concentration had a significant correlation with point‐of‐care PT (R = 0.82, P < .001) and RapidTEG‐TEG, TF100‐TEG, and TF3700‐TEG (R = 0.76, P < .001; R = 0.82, P < .001; and R = 0.83, P < .001, respectively). Conclusions and Clinical Importance Overall, a 1.5‐1.9 × delay in PT and R values of TEG 3 hours after rivaroxaban administration is required to achieve therapeutic anti‐Xa concentrations of rivaroxaban in canine plasma. The R values of TEG, specifically using tissue factors (RapidTEG, TF100, TF3700) and point‐of‐care PT for rivaroxaban can be used practically for therapeutic monitoring of rivaroxaban in dogs.