Lepirudin is a direct thrombin inhibitor obtained by recombinant technology from the medicinal leech and used for treatment of heparin-induced thrombocytopenia (HIT). Lepirudin was the first direct thrombin inhibitor approved and most frequently used for the treatment of patients with HIT. The efficacy of lepirudin for HIT has been shown to improve general outcomes in patients with HIT, reducing a primary composite endpoint of new thrombosis, all-cause amputation, and all-cause death. Lepirudin forms a stable non-covalent complex with alpha-thrombin, thereby abolishing its ability to cleave fibrinogen and initiate the clotting cascade. It is a highly potent, selective, and essentially irreversible inhibitor of thrombin and clot-bond thrombin. Lepirudin is identical to natural hirudin except for substitution of leucine for isoleucine at the N-terminal end of the molecule and the absence of a sulfate group on the tyrosine at position 63.