From the Guidelines
Anti-Xa targets refer to the inhibition of activated factor X, which is the primary mechanism by which anticoagulants such as rivaroxaban, apixaban, and edoxaban exert their anticoagulant effect. The targets of Anti-Xa (Anti-Factor Xa) are the factor Xa inhibitors, which include rivaroxaban, apixaban, and edoxaban, as well as low-molecular-weight heparin (LMWH) such as enoxaparin 1. These anticoagulants work by inhibiting the activity of factor Xa, which is a critical component of the coagulation cascade. The anti-Xa assay measures the drug's ability to inhibit activated factor X, which provides a more accurate assessment of anticoagulant activity than PTT or INR, which are used for monitoring unfractionated heparin and warfarin, respectively 1.
Some key points to note about Anti-Xa targets include:
- The standard therapeutic anti-Xa target range for treatment of venous thromboembolism is 0.5-1.0 IU/mL for twice-daily dosing and 1.0-2.0 IU/mL for once-daily dosing, measured at peak levels (4 hours post-dose) 1.
- For prophylactic dosing, the target range is typically 0.2-0.5 IU/mL 1.
- Common factor Xa inhibitors include rivaroxaban, apixaban, and edoxaban, as well as LMWHs such as enoxaparin, dalteparin, and tinzaparin 1.
- Anti-Xa monitoring is not routinely needed for most patients but is recommended in specific populations including those with severe renal impairment (CrCl <30 mL/min), extremes of body weight (<50 kg or >150 kg), pregnancy, and children 1.
It's worth noting that the management of bleeding and coagulopathy following major trauma in patients treated with factor Xa antagonists is a complex issue, and high-dose prothrombin complex concentrate (PCC) treatment may be initiated if anti-factor Xa activity is detected 1. However, the involvement of a hematologist with expertise in coagulation should be considered.
From the FDA Drug Label
Apixaban is a selective inhibitor of FXa. It does not require antithrombin III for antithrombotic activity. Apixaban inhibits free and clot-bound FXa, and prothrombinase activity. The target of Anti-Xa (Anti-Factor Xa) is Factor Xa (FXa).
- The targets include:
- Free FXa
- Clot-bound FXa
- Prothrombinase activity 2
From the Research
Targets of Anti-Xa (Anti-Factor Xa)
The targets of Anti-Xa (Anti-Factor Xa) are factor Xa inhibitors, which are a novel therapeutic class for the treatment of nonvalvular atrial fibrillation 3. These inhibitors work by blocking the activity of factor Xa, a key enzyme in the coagulation cascade. The main indications for factor Xa inhibitors are:
- Prevention of stroke and systemic embolism in adults with nonvalvular atrial fibrillation
- Deep vein thrombosis
- Pulmonary embolism
Mechanism of Action
Factor Xa inhibitors, such as rivaroxaban, apixaban, and edoxaban, inhibit thrombin formation by blocking the activity of factor Xa 4, 5. They are oral selective anti-Xa inhibitors with well-predictive pharmacokinetics and pharmacodynamics. These inhibitors have been shown to be effective in reducing the risk of stroke and systemic embolism in patients with nonvalvular atrial fibrillation, with a trend towards lowering stroke and systemic embolization compared to warfarin 4.
Key Characteristics
Some key characteristics of factor Xa inhibitors include:
- Oral administration
- Selective inhibition of factor Xa
- Well-predictive pharmacokinetics and pharmacodynamics
- Variation in dosing regimens, including once-daily and twice-daily dosing
- Potential interactions with other drugs, such as inhibitors of cytochrome P450 and P-glycoprotein
- Inability to reverse their anticoagulant effects
Clinical Trials
Several clinical trials have investigated the efficacy and safety of factor Xa inhibitors for stroke prevention in atrial fibrillation. These trials have shown that factor Xa inhibitors, such as apixaban and rivaroxaban, are superior or noninferior to warfarin in terms of efficacy and safety 3, 6, 5. Additionally, studies have monitored drug plasma concentration and coagulation activity to investigate the safety profiles of these inhibitors 7.