Several other direct thrombin inhibitors are derived chemically from hirudin. Hirudin is the most potent natural inhibitor of thrombin. One active anticoagulant component of leech saliva is a small protein, hirudin. Lepirudin is a recombinant hirudin derived from yeast cells. Hirudin (and related substances) are synthesised using recombinant techniques. Bivalirudin, a 20 amino acid polypeptide, is a synthetic analog of hirudin. Native hirudin, a 65-amino-acid polypeptide, is produced in the parapharyngeal glands of medicinal leeches. After piercing the skin, they suck out blood whilst injecting anticoagulants (hirudin) and anaesthetics. The procedure lasted only 15 minutes, and hirudin served as the anticoagulant. However, recombinant techniques can be used to produce homogeneous preparations of hirudin. Natural hirudin contains a mixture of various isoforms of the protein. Full length hirudin is made up of 65 amino acids. "Olympia" (2013), "Future Politics" (2017), and HiRUDiN (2020). The first DTI was actually hirudin, which became more easily available with genetic engineering.