One of the followig opioid derivatives is a paial agonist as well as antagonist-
**Core Concept**
Opioid derivatives can exhibit various receptor binding profiles, including partial agonism and antagonism. This phenomenon is crucial in understanding their therapeutic effects and potential side effects. Buprenorphine is a notable example of a partial agonist-antagonist opioid.
**Why the Correct Answer is Right**
Buprenorphine acts as a partial agonist at the μ-opioid receptor, producing analgesia with a lower risk of respiratory depression compared to full agonists like morphine. Simultaneously, it acts as an antagonist at the κ-opioid receptor, which contributes to its ceiling effect on respiratory depression. This dual action makes buprenorphine useful in managing opioid use disorder and treating chronic pain.
**Why Each Wrong Option is Incorrect**
* **Option A:** Methadone is a full opioid agonist, primarily acting on the μ-opioid receptor to produce analgesia and dependence.
* **Option B:** Naloxone is a pure opioid antagonist, used to reverse opioid overdose by competitively inhibiting opioid receptors.
* **Option C:** Pentazocine is a mixed agonist-antagonist opioid, but it primarily acts as an agonist at the κ-opioid receptor, producing analgesia and psychotomimetic effects.
**Clinical Pearl / High-Yield Fact**
Buprenorphine's partial agonist activity at the μ-opioid receptor makes it a safer alternative to full agonists for managing chronic pain and opioid use disorder. However, its ceiling effect on respiratory depression may not be as pronounced in patients with impaired liver function.
**Correct Answer:** C. Pentazocine