» Thrombin conforms to the regulations of the FDA concerning biologics (see
Biologics 1041). It is a sterile, freeze-dried powder derived from bovine plasma containing the protein substance prepared from prothrombin through interaction with added thromboplastin in the presence of calcium. It is capable, without the addition of other substances, of causing the clotting of whole blood, plasma, or a solution of fibrinogen. Its potency is determined in U.S. Units in terms of the U.S. Standard Thrombin in a test comparing clotting times of fibrinogen solution.