Arixtra (Fondaparinux) is an anticoagulant that helps prevent the formation of blood clots. Fondaparinux is used to prevent a type of blood clot called deep vein thrombosis (DVT), which can lead to blood clots in the lungs (pulmonary embolism). A DVT can occur after certain types of surgery. Fondaparinux is also used together with warfarin (Coumadin, Jantoven) to treat DVT, including pulmonary embolism.