Bivalirudin is a synthetic 20 residue peptide (thrombin inhibitor) which reversibly inhibits thrombin. Once bound to the active site, thrombin cannot activate fibrinogen into fibrin, the crucial step in the formation of thrombus. It is administered intravenously. Because it can cause blood stagnation, it is important to monitor changes in hematocrit, activated partial thromboplastin time, international normalized ratio and blood pressure. This compound belongs to the class of organic compounds known as polypeptides. These are peptides containing ten or more amino acid residues.