Comparison of Anti-Xa Activity in Patients Receiving Apixaban or Rivaroxaban

Background: There is no established method for monitoring the anticoagulant effects of apixaban and rivaroxaban. Linear correlation between serum levels and anti-Xa activity has been shown, with r 2 ranging from 0.88 to 0.99. However, there are minimal data in patients receiving apixaban 5 mg twice daily or rivaroxaban 20 mg once daily. Objective: To evaluate the anti-Xa activity and serum levels at those doses and compare the trough anti-Xa activity. Methods: This was a single-center prospective study,approved by the institutional review board. Patients on an inappropriate dose or receiving an interacting drug were excluded. Blood samples were drawn 0.5 to 3 hours before a dose for both agents, 2 to 3 hours after an apixaban dose, and 12 to 16 hours after a rivaroxaban dose. Anti-Xa activity and serum levels were determined, and correlation was done via regression analysis. Trough anti-Xa activity was compared using a t-test. Results: The study enrolled 88 patients receiving each drug. The r 2 values were 0.79 and 0.87 for apixaban and rivaroxaban, respectively. The mean trough anti-Xa activity was 1.79 ± 0.96 IU/mL for apixaban and 1.25 ± 0.88 IU for rivaroxaban ( P < 0.01). The trough sample was drawn a mean of 1.3 and 1.8 hours prior to the next dose for apixaban and rivaroxaban, respectively ( P < 0.01). Conclusions: Good correlation was shown between anti-Xa activity and serum levels. The clinical utility of monitoring anti-Xa activity and the significance of the difference in trough anti-Xa activity for these agents remains to be established.