A nurse is caring for a client who is prescribed warfarin via oral (PO) route. Two hours after the administration of warfarin, the client reports having dark tarry stools and petechiae. Based on the client's presenting symptoms, which of the following options is an antidote for warfarin toxicity?

The correct answer is A: Vitamin K1. Warfarin is an anticoagulant that inhibits vitamin K-dependent clotting factors. Dark tarry stools and petechiae are signs of bleeding, indicating warfarin toxicity. Vitamin K1 is the antidote for warfarin toxicity as it helps replenish the depleted vitamin K levels needed for clotting factor synthesis. Protamine sulfate is an antidote for heparin, not warfarin. Heparin (choice C) is another anticoagulant and not used to reverse warfarin toxicity. Digibind (choice D) is an antidote for digoxin toxicity, not warfarin.