<s>[INST] context: Heparin is reversed by the administration of protamine sulfate. Spontaneous retroperitoneal hemorrhage is a rare but potentially fatal complication of anticoagulation. Heparin is much more frequently associated with spontaneous retroperitoneal hemorrhage than are oral agents. Advanced patient age and poor regulation of coagulation times also increase the likelihood of bleeding complications. Most cases of retroperitoneal hemorrhage present with flank pain and signs of peritoneal irritation suggestive of an acute intra-abdominal process. CT scans are most useful in confirming the diagnosis and following the course of the bleeding. Successful management is usually nonoperative and consists of the discontinuation of anticoagulants, reversal of anticoagulation, possible transfusion of clotting factors, and repletion of intravascular volume with intravenous fluids. Warfarin inhibits synthesis of vitamin K-dependent clotting factors, whereas heparin potentiates antithrombin III activity. Aprotinin is a protease inhibitor that decreases the inflammatory and fibrinolytic response and is used in patients undergoing cardiopulmonary bypass surgery to reduce bleeding complications. Lepirudin is an anticoagulant that is used in patients who develop heparin-induced thrombocytopenia. Thrombin can be used topically as a hemostatic agent. [/INST] question: A 72-year-old woman who is planning to undergo ventral hernia repair is on warfarin for atrial fibrillation. She is advised to cease her warfarin several days before her surgery and is hospitalized preoperatively for heparinization. During her hospital stay, she complains of severe abdominal and flank pain. Her prothrombin time (PT) is normal, but her activated paial thromboplastin time (aPTT) is elevated. An abdominal CT scan demonstrates a large retroperitoneal hematoma. Which of the following should be administered to reverse the effects of the heparin? | options: A: Thrombin B: Vitamin K C: Protamine sulfate D: Aprotinin | answer: C </s>