Which of the following is an example of an opioid partial antagonist or mixed opioid agonist/antagonist?

Which of the following is an example of an opioid partial antagonist or mixed opioid agonist/antagonist?

• A. Naloxone
• B. Buprenorphine
• C. Morphine
• D. Fentanyl

Answer: (B)

An opioid partial antagonist or mixed opioid agonist/antagonist is a drug that binds to opioid receptors and produces only partial activation, while often blocking or competing with other opioids at the same receptor. Buprenorphine fits this profile because it is a partial agonist at the mu opioid receptor—providing analgesia but with a ceiling to respiratory depression—and it acts with high affinity, meaning it can outcompete other opioids. It also has antagonist activity at kappa receptors, which contributes to its distinct pharmacologic profile. This combination—partial mu agonism with kappa antagonism and strong receptor binding—explains why buprenorphine can precipitate withdrawal in someone dependent on full agonists (due to displacement and limited intrinsic activity) yet offers safer analgesia with a ceiling effect on respiratory depression. In contrast, full mu agonists like morphine and fentanyl produce full effects at the mu receptor without a ceiling, and naloxone is a pure antagonist with no agonist activity.

An opioid partial antagonist or mixed opioid agonist/antagonist is a drug that binds to opioid receptors and produces only partial activation, while often blocking or competing with other opioids at the same receptor. Buprenorphine fits this profile because it is a partial agonist at the mu opioid receptor—providing analgesia but with a ceiling to respiratory depression—and it acts with high affinity, meaning it can outcompete other opioids. It also has antagonist activity at kappa receptors, which contributes to its distinct pharmacologic profile.

This combination—partial mu agonism with kappa antagonism and strong receptor binding—explains why buprenorphine can precipitate withdrawal in someone dependent on full agonists (due to displacement and limited intrinsic activity) yet offers safer analgesia with a ceiling effect on respiratory depression. In contrast, full mu agonists like morphine and fentanyl produce full effects at the mu receptor without a ceiling, and naloxone is a pure antagonist with no agonist activity.