A nurse is caring for a client who is receiving warfarin (Coumadin) therapy to prevent a deep vein thrombosis. Which of the following medications should the nurse have available in the event of an overdose?

Choice A rationale Epinephrine is an adrenergic agonist and a potent vasoconstrictor, primarily used to treat severe allergic reactions (anaphylaxis) and cardiac arrest by stimulating alpha and beta receptors. It would not reverse the anticoagulant effects of warfarin, which acts by inhibiting vitamin K epoxide reductase in the coagulation cascade. Its mechanism of action is unrelated to reversing excessive anticoagulation. Choice B rationale Protamine sulfate is the specific antidote for heparin overdose, not warfarin. Protamine is a highly basic protein that forms a stable, inactive complex with the highly acidic heparin molecule, thereby neutralizing its anticoagulant effect. It has no effect on the mechanism of action of warfarin, which interferes with vitamin K-dependent clotting factors synthesis. Choice C rationale Atropine is an anticholinergic (parasympatholytic) agent used to increase heart rate in cases of symptomatic bradycardia by blocking the effects of acetylcholine at muscarinic receptors. It does not interact with the clotting cascade or the pharmacodynamics of warfarin, which requires replacement of the necessary clotting factors or its cofactor. Choice D rationale Vitamin K (Phytonadione) is the essential cofactor for the synthesis of coagulation factors II, VII, IX, and X in the liver, which are inhibited by warfarin. Administering Vitamin K bypasses the warfarin-induced block, promoting the production of functional clotting factors and thus reversing excessive anticoagulation, which is reflected by a prolonged International Normalized Ratio (INR) (therapeutic range 2.0-3.0).