Which of the following best describes the duration of action of naltrexone compared to naloxone?

Which of the following best describes the duration of action of naltrexone compared to naloxone?

• A. Longer duration of action
• B. Shorter duration of action
• C. Same duration
• D. Not related to naloxone

Answer: (A)

The concept being tested is how long opioid receptor blockade lasts with different antagonists. Naloxone is a fast-acting, short-duration antagonist used to reverse opioid effects quickly; it binds to μ-receptors and is cleared from the body relatively quickly, so its effects typically last about an hour or two and may require repeat dosing in overdose scenarios. Naltrexone, in contrast, has a much longer duration because of its higher receptor affinity and slower clearance, so a single dose can block opioid effects for roughly a day or more (often 24–72 hours). That’s why naltrexone is described as having a longer duration of action than naloxone. The other ideas don’t fit: it isn’t equally long-acting, it isn’t shorter, and it isn’t unrelated to naloxone, since they are both opioid receptor antagonists with distinctly different durations.

The concept being tested is how long opioid receptor blockade lasts with different antagonists. Naloxone is a fast-acting, short-duration antagonist used to reverse opioid effects quickly; it binds to μ-receptors and is cleared from the body relatively quickly, so its effects typically last about an hour or two and may require repeat dosing in overdose scenarios. Naltrexone, in contrast, has a much longer duration because of its higher receptor affinity and slower clearance, so a single dose can block opioid effects for roughly a day or more (often 24–72 hours). That’s why naltrexone is described as having a longer duration of action than naloxone. The other ideas don’t fit: it isn’t equally long-acting, it isn’t shorter, and it isn’t unrelated to naloxone, since they are both opioid receptor antagonists with distinctly different durations.