Opioid analgesics

Wikis > Pharmacology > Analgesic Drugs > Opioid analgesics

Opioid analgesics:
Drugs with action similar to morphine.
Can be:
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.

Opioid receptors:
• 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)

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