Full opioid agonists vs Partial agonists and antagonists
How to tell Full opioid agonists and Partial agonists and antagonists apart when a board question makes them look alike.
Full agonists maximally activate mu receptors; partial agonists cap activation; antagonists block activation.
Side by side
Morphine/fentanyl/oxycodone pattern with full mu activation, analgesia, euphoria, constipation, miosis, and respiratory depression.
Buprenorphine partial mu agonism can precipitate withdrawal; naloxone/naltrexone antagonize opioid receptors without agonist effect.
Full agonists activate mu receptors with high intrinsic activity.
Partial agonists have high affinity but lower intrinsic activity, while antagonists block receptors and reverse or prevent opioid effect.
Overdose triad of coma, miosis, and respiratory depression points full agonist toxicity.
Buprenorphine displacement withdrawal points partial agonist; naloxone rapid reversal points antagonist.
The trap
High receptor affinity can make a partial agonist behave like an antagonist in someone using full agonists.
The repair move
For opioid drugs, separate receptor activation strength from receptor binding affinity.
Try a free question
CoreA patient receives morphine for severe pain and develops miosis, constipation, euphoria, and respiratory depression. Which receptor role best fits?
Show answer and explanation
Answer: A. Full mu-opioid agonist. Full mu agonists such as morphine or fentanyl can produce maximal opioid effect and respiratory depression.
Why the other choices are tempting
- B. Partial mu agonists have ceiling effects and can precipitate withdrawal in dependent patients.
- C. Pure antagonists reverse opioid effects rather than produce euphoria/respiratory depression.
- D. Kappa-only antagonist is not the classic morphine mechanism.
- E. Alpha-2 agonists reduce sympathetic outflow, not mu-opioid analgesia.
Flashcards
Tap a card to flip it.
What is the fastest separator for Full opioid agonists vs Partial agonists and antagonists?
Full agonists maximally activate mu receptors; partial agonists cap activation; antagonists block activation.
What clue should make you choose Full opioid agonists?
Morphine/fentanyl/oxycodone pattern with full mu activation, analgesia, euphoria, constipation, miosis, and respiratory depression.
Quick answers
What is the fastest way to tell Full opioid agonists from Partial agonists and antagonists?
Full agonists maximally activate mu receptors; partial agonists cap activation; antagonists block activation.
What is the key clue for Full opioid agonists?
Morphine/fentanyl/oxycodone pattern with full mu activation, analgesia, euphoria, constipation, miosis, and respiratory depression.
What is the key clue for Partial agonists and antagonists?
Buprenorphine partial mu agonism can precipitate withdrawal; naloxone/naltrexone antagonize opioid receptors without agonist effect.
What is the common trap with Full opioid agonists vs Partial agonists and antagonists?
High receptor affinity can make a partial agonist behave like an antagonist in someone using full agonists.