Unfractionated heparin and other antithrombin mediated anticoagulants.

Clinical practice over the past decade has evolved to include new agents, LMWH and synthetic polysaccharides, that bind to and enhance the activity of antithrombin similar to UFH. These drugs differ from UFH since their anticoagulant effect consists predominantly, or entirely, of anti-Xa activity. More important, the new drugs have greater predictability with regard to dosing. In clinical studies the new agents have proven as good as or better than UFH with regard to efficacy and toxicity. The synthetic polysaccharide may possess the greatest efficacy, but possibly with increased bleeding risk. However, UFH still has one advantage over these agents, the ability of its anticoagulant effect to undergo essentially complete reversal with an available drug, protamine sulfate. Thus, clinical situations favoring UFH over these newer parenteral agents still exist.