DTIs inhibit thrombin by two ways; bivalent DTIs block simultaneously the active site and exosite 1 and act as competitive inhibitors of fibrin, while univalent DTIs block only the active site and can therefore both inhibit unbound and fibrin-bound thrombin. In contrast, heparin drugs bind in exosite 2 and form a bridge between thrombin and antithrombin, a natural anticoagulant substrate formed in the body, and strongly catalyzes its function. But heparin can also form a bridge between thrombin and fibrin which binds to exosite 1 which protects the thrombin from inhibiting function of heparin-antithrombin complex and increases thrombins affinity to fibrin. DTIs that bind to the anion-binding site have shown to inactivate thrombin without disconnecting thrombin from fibrin, which points to a separate binding site for fibrin. DTIs arent dependent to cofactors like antithrombin to inhibit thrombin so they can both inhibit free/soluble thrombin as well as fibrin bound thrombin unlike heparins. The inhibition is either irreversible or reversible. Reversible inhibition is often linked to lesser risk of bleeding. Due to this action of DTIs they can both be used for prophylaxis as well as treatment for embolisms/clots.