The following drugs are reversible competitive antagonists:

Correct Answer: D

Rationale: Naloxone is a reversible competitive antagonist at opioid receptors, reversing opioid effects by competing for binding without activating the receptor.

Correct Answer: C

Rationale: An agonist is a substance that binds to a receptor and triggers a biological response. By activating the receptor, an agonist mimics the action of the body's natural ligand that typically binds to the receptor. This activation may lead to a cascade of events within the cell, resulting in a specific physiological response. In contrast, antagonists block the receptor from being activated, while agonists work by binding to the receptor and initiating the desired response.

Correct Answer: B

Rationale: Protamine is the antidote for Heparin. Heparin is an anticoagulant medication that prevents the formation of blood clots. In case of an overdose of Heparin or if there is a need to reverse its effects quickly (such as during surgery), Protamine is administered as the specific antidote. Protamine works by binding to Heparin and neutralizing its anticoagulant effects. Therefore, Protamine is the appropriate antidote to counteract the effects of Heparin.

Correct Answer: D

Rationale: Naloxone is a reversible competitive antagonist at opioid receptors, reversing opioid effects by competing for binding without activating the receptor.

Correct Answer: A

Rationale: Nausea is one of the early manifestations of lithium toxicity. It is important to monitor for this symptom in patients taking lithium to detect toxicity early and prevent more serious complications. Hypotension and renal failure are more severe manifestations of lithium toxicity that occur at later stages. Muscle weakness is not typically associated with early lithium toxicity.