Thrombin is the enzyme that converts fibrinogen to fibrin. The prothrombin obtained from the fractionation of plasma is washed with distilled water and dissolved in citrate saline. It is converted to thrombin by adjusting the pH to 7 and by adding thromboplastin and calcium ions. The solution is filtered and freeze-dried, and the air in the containers is replaced with nitrogen. It is reconstituted with saline when required.

Uses: The fibrin clot produced when thrombin is mixed with fibrinogen is used in surgery to suture severed nerves and to assist adhesion of skin grafts. Since the fibrin is human, it is tolerated well by the body and new cells penetrate it rapidly.