A nurse is caring for a client who has thrombophlebitis and is receiving a continuous heparin infusion. Which of the following medications should the nurse have available to reverse heparin's effects?

The correct answer is D: Protamine sulfate. Protamine sulfate is used as an antidote for heparin overdose as it reverses the anticoagulant effects of heparin by binding to it. This forms a stable salt complex that neutralizes the effects of heparin. Vitamin K (choice A) is used to reverse the effects of warfarin, not heparin. Deferoxamine (choice B) is used for iron toxicity. Acetylcysteine (choice C) is used for acetaminophen overdose. Therefore, the nurse should have protamine sulfate available to reverse heparin's effects.