From the FDA Drug Label
Apixaban is a selective inhibitor of FXa. It does not require antithrombin III for antithrombotic activity. The patient is Antithrombin III Positive is not relevant as Eliquis (apixaban) does not require antithrombin III for its antithrombotic activity 1.
- Key Point: The presence or absence of antithrombin III does not affect the mechanism of action of apixaban.
- Clinical Decision: The use of Eliquis (apixaban) is not dependent on the patient's antithrombin III status.
From the Research
Antithrombin III levels are typically not affected by Eliquis (apixaban) use, and patients taking Eliquis can have normal antithrombin III levels because Eliquis works as a direct factor Xa inhibitor, which is a different mechanism than antithrombin III. This is supported by the study 2, which provides a comprehensive evaluation of apixaban in the treatment of venous thromboembolism, and notes that apixaban offers several advantages over historical therapy for the treatment and secondary prevention of VTE.
The mechanism of action of Eliquis is as a direct factor Xa inhibitor, which means it directly binds to and inhibits factor Xa without requiring antithrombin III as a cofactor 3. This is in contrast to antithrombin III, which is a natural anticoagulant protein that inhibits thrombin and other clotting factors. As a result, laboratory tests measuring antithrombin III activity or levels should remain within normal ranges for patients on Eliquis, assuming they don't have an underlying antithrombin deficiency.
It's also important to note that Eliquis can affect other coagulation tests like PT, INR, and anti-Xa assays 4. If you're monitoring a patient on Eliquis, specific anti-Xa assays calibrated for apixaban are more appropriate for measuring the anticoagulant effect rather than antithrombin III levels. The study 4 found that apixaban showed fewer effects in vitro than have been shown for rivaroxaban, another direct FXa inhibitor, and that chromogenic anti-FXa assays showed linear dose-response curves with apixaban.
Overall, the evidence suggests that antithrombin III levels are not significantly affected by Eliquis use, and that patients taking Eliquis can have normal antithrombin III levels. However, it's always important to consider the individual patient's underlying conditions and other medications they may be taking when interpreting laboratory results.