Naloxone interacts with fentanyl by which mechanism?

• A. Acts as a competitive agonist displacing fentanyl from the receptor
• B. Acts as a competitive antagonist that displaces fentanyl from the receptor
• C. Irreversibly binds mu receptors
• D. Blocks calcium channels

Answer: (B)

Naloxone reverses opioid effects by binding to mu-opioid receptors with high affinity but no intrinsic activity, acting as a competitive antagonist. This means it occupies the receptor sites and displaces fentanyl (an opioid agonist), blocking fentanyl’s ability to activate the receptor and thereby reversing respiratory depression and sedation. Because naloxone is shorter-acting than many synthetic opioids, its effects can wear off and re-narcotization can occur, necessitating additional dosing or infusion. It does not irreversibly bind the receptor, nor does it block calcium channels; its action is specifically competitive antagonism at mu receptors that explains the reversal of fentanyl’s effects.