Which antidote reverses heparin if excessive bleeding occurs?

• A. Vitamin K
• B. Fresh frozen plasma
• C. Calcium gluconate
• D. Protamine sulfate

Answer: (D)

Reversing heparin’s anticoagulant effect is achieved with protamine sulfate. Heparin works by binding antithrombin III and thereby inactivating thrombin and factor Xa, which prevents clot formation. When bleeding occurs from excess heparin, giving protamine sulfate binds to the heparin molecules in a one-to-one fashion and forms a stable, inactive complex, quickly restoring the blood’s ability to clot. The reversal is most effective when protamine is given promptly and dosed to neutralize the amount of heparin that has circulated recently. Dosing is guided by how much heparin was given and over what time frame, with careful monitoring of clotting status.

Vitamin K reverses the effects of warfarin, not heparin, because warfarin works by depleting vitamin K–dependent clotting factors, which vitamin K directly replenishes. Fresh frozen plasma provides clotting factors but does not neutralize heparin itself, so it’s not the targeted antidote for heparin excess. Calcium gluconate is used for correcting hypocalcemia or counteracting citrate effects in transfusion, not for reversing heparin.