A yeast cell-derived recombinant polypeptide related to the naturally occurring, leech-derived anticoagulant hirudin. Lepirudin directly binds to and inactivates thrombin, producing dose-dependent increases in the activated partial thromboplastin time (aPTT) and prothrombin time (PT). The mechanism of action of this agent is independent of antithrombin III and is not inhibited by platelet factor 4. Natural hirudin, a family of highly homologous isopolypeptides, is produced in trace amounts by the leech Hirudo medicinalis. or A drug that inhibits blood clotting. It is being studied in cancer treatment.