Which drug is utilized to reverse the effects of heparin?

Protamine sulfate is the medication specifically used to reverse the effects of heparin, a widely used anticoagulant. Heparin works by inhibiting certain clotting factors in the blood, which helps prevent the formation of unwanted blood clots. However, if a patient needs to counteract this anticoagulant effect—such as in cases of surgery, bleeding complications, or overdose—protamine sulfate is administered. It acts by binding to heparin, forming a stable complex that neutralizes its anticoagulant properties.

Understanding the roles of the other options provides additional clarity. Vitamin K is primarily associated with reversing the effects of anticoagulants like warfarin, not heparin. Fibrinogen is a clotting factor itself and does not have a reversing effect but rather assists in the clotting process. Calcium plays a role in various physiological functions, including clotting, but is not a reversing agent for heparin. Thus, protamine sulfate is uniquely suited for this purpose, confirming why it is the correct answer.