What is the name of an antagonist pharmacological agent that is administered systemically?

The correct answer is Protamine, which is a specific antagonist to heparin, an anticoagulant. Protamine is used in clinical practice to reverse the effects of heparin during or after surgical procedures when rapid anticoagulation reversal is necessary, such as in cases of excessive bleeding.

Protamine works by binding to heparin in a 1:1 ratio, thus neutralizing its pharmacological effects. This is particularly important during procedures that require the maintenance of a sterile field and controlled bleeding. The ability to administer an antagonist like protamine systemically makes it essential in managing heparin-related complications effectively.

Acetaminophen and ibuprofen are analgesics and do not serve as antagonists; they provide pain relief and manage inflammation but do not counteract anticoagulation. Heparin is an anticoagulant itself and would not fit the definition of an antagonist in this context. Therefore, protamine stands out as the correct answer based on its pharmacological role and systemic administration.