Fondaparinux is an injectable synthetic pentasaccharide that binds to antithrombin, causes a conformational change, and reduces the affinity of Factor Xa by a factor of 300. This anticoagulant needs to be injected q12h.
The hypermethylated version of fondaparinux, idraparinux, has even higher affinity for antithrombin, so it can be injected q72h. But there is a high risk of bleeding.
Idraparinux + biotin = idrabiotaparinux, which can be injected q72h BUT also neutralized with IV biotin.
Source: Kazmi and Lwaleed, "New anticoagulants: how to deal with treatment failure and bleeding complications," British Journal of Clinical Pharmacology, vol. 72, no. 4 (Oct. 2011).