What is the mechanism of action of naloxone and when is it indicated?

• A. Noncompetitive antagonist at mu receptors; used for pain relief.
• B. Partial agonist at mu receptors; used to treat addiction.
• C. Competitive antagonist at mu opioid receptors; used to reverse opioid overdose or sedation.
• D. Agonist at kappa receptors; used to induce analgesia.

Answer: (C)

Naloxone works by blocking opioid effects at the receptor sites, specifically as a competitive antagonist at mu opioid receptors. It has a higher affinity for these receptors than most opioid agonists, so it displaces the opioid from the receptor and rapidly reverses the main dangerous effects of opioid use, such as respiratory depression and sedation. Because it antagonizes the receptor without activating it, it doesn’t provide analgesia and can precipitate withdrawal in people or animals dependent on opioids.

Indicated when there is suspected opioid overdose or opioid-induced sedation, including reversals during anesthesia or in veterinary patients receiving opioid analgesia. Since it’s competitive, its effectiveness depends on the amount of opioid present; higher or longer-acting opioids may require repeated dosing or continuous monitoring and redosing. It’s not used for non-opioid overdoses and must be used with caution to avoid abrupt withdrawal or worsened pain in opioid-tolerant individuals.