What is the antidote for heparin?

Protamine sulfate is the antidote for heparin because it directly neutralizes the anticoagulant effects of heparin by binding to it and forming an inactive complex. Heparin is an anticoagulant medication that works by inhibiting thrombin and factor Xa, which are crucial for the coagulation cascade. In situations where there is an excessive anticoagulation or if a surgical procedure is necessary, protamine sulfate can be administered to reverse the effects of heparin, allowing for normal blood clotting to resume.

Vitamin K is not effective for heparin reversal; rather, it is used for reversing the effects of warfarin, another anticoagulant with a different mechanism of action. Thrombin is an enzyme that plays a role in the coagulation process and would not serve as an antidote for heparin. Acetylcysteine is primarily used as an antidote for acetaminophen (paracetamol) overdose and has no relevance in the context of heparin therapy. Therefore, the appropriate answer is protamine sulfate, as it effectively counteracts the action of heparin.