Apixaban and Rivaroxaban Directly Inhibit Factor Xa
Apixaban and rivaroxaban are direct factor Xa inhibitors that block factor Xa, thereby preventing the conversion of prothrombin to thrombin. Warfarin acts indirectly through vitamin K antagonism, and heparin requires antithrombin as a cofactor to inhibit multiple coagulation factors including factor Xa 1, 2.
Mechanism of Action
Direct Factor Xa Inhibitors (Apixaban, Rivaroxaban)
Both apixaban and rivaroxaban selectively and directly inhibit factor Xa without requiring cofactors like antithrombin. They bind directly to the active site of factor Xa, blocking its interaction with substrates 2, 3. This mechanism:
- Inhibits free factor Xa in plasma
- Inhibits factor Xa bound to the prothrombinase complex
- Inhibits clot-associated factor Xa 2
By blocking factor Xa, these drugs prevent the conversion of prothrombin (factor II) to thrombin, thereby reducing thrombin generation and subsequent fibrin formation 4, 5, 3.
Rivaroxaban is a competitive, reversible factor Xa inhibitor with >10,000-fold selectivity for factor Xa over other serine proteases 2. Apixaban similarly demonstrates high selectivity and reversibly inhibits both free and prothrombinase complex-bound factor Xa 5.
Why Not the Other Options
Warfarin is a vitamin K antagonist that indirectly affects multiple coagulation factors (II, VII, IX, X) by inhibiting their synthesis in the liver—it does not directly block factor Xa 6.
Heparin works indirectly by binding to antithrombin III, which then inhibits multiple activated coagulation factors including factors Xa and IIa (thrombin). Heparin requires antithrombin as a cofactor and does not directly inhibit factor Xa 4, 7.
Clinical Distinction
The direct oral anticoagulants (DOACs) are classified by their mechanism 8, 9:
- Direct thrombin inhibitors: Dabigatran (inhibits factor IIa/thrombin)
- Direct factor Xa inhibitors: Rivaroxaban, apixaban, edoxaban (inhibit factor Xa)
The key advantage of direct factor Xa inhibitors is their ability to inhibit factor Xa in all locations—free in plasma, bound in the prothrombinase complex, and incorporated into clots—unlike indirect inhibitors (heparin/antithrombin complex) which cannot effectively inhibit factor Xa once it's incorporated into the prothrombinase complex 2.
Important Caveat
While both apixaban and rivaroxaban are correct answers as direct factor Xa inhibitors, rivaroxaban was specifically mentioned in your question as "Gatra band" (likely rivaroxaban). Both drugs share the same mechanism of directly blocking factor Xa to prevent prothrombin-to-thrombin conversion 1, 5, 2.