Drugs with action similar to morphine.
1) natural (eg opium, codeine)
2) synthetic (eg diamorphine, methadone, levorphanol, pethidine, phenazocine)
Act by binding to opiate receptors in CNS alter perception and emotional response to pain.
• three types – mu, kappa, delta
• act mostly through mu receptor and weakly through kappa receptors
• if mu receptors activated analgesia, respiratory depression, sedation and sense of euphoria; mu receptors also related to physical dependence.
• activated of kappa receptors analgesia and sedation
Drugs that act at opioid receptors:
1) Opioid agonists:
• activate both mu and kappa receptors
• can be strong acting (eg morphine, methadone, oxymorphine, fentanyl, levorphanol) or moderate to strong acting (eg codeine, oxycodone, hydrocodone, propoxyphene)
2) Opioid antagonists:
• do not activate receptors
• used to reverse effects of agonists
• eg naloxone
3) Agonist-antagonist opioids:
• can be antagonist at mu receptors and agonist at kappa receptor (eg pentazocine, butorphanol)
• or agonist at mu receptor and antagonists at kappa receptors (eg buprenorphine)