Which antidote reverses warfarin effects?

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

Answer: (B)

Warfarin works by blocking vitamin K–dependent activation of coagulation factors, so reversing its effects means replenishing vitamin K to restore the liver’s ability to make those factors again. Giving vitamin K supplies the vitamin the liver needs, allowing the production of functional factors II, VII, IX, and X, which gradually restores normal clotting. The reversal starts within hours and is typically complete over a day or two, depending on how quickly new factors are made. In urgent bleeding, additional options like fresh frozen plasma or prothrombin complex concentrates can provide clotting factors immediately, but the specific antidote that counteractswarfarin’s mechanism is vitamin K. Protamine sulfate acts on heparin, calcium gluconate isn’t used to reverse anticoagulation, and fresh frozen plasma provides factors but isn’t the antidote itself.