L6 Narcotic (Opoid) Analgesics Flashcards
What was opioid peptides previously known as?
Endorphins, collectively
Which opioid receptor subtype is probably the major one?
mu
Which opioid receptor subtype results in dysphoria (unease/discomfort)?
kappa
Examples of opioid agonists used for analgesia
codeine, morphine, pethidine
Examples of opioid agonists used for anaesthetic adjuvant
fentanyl
Examples of opioid agonists used for cough suppressant/antitussive
codeine
Examples of opioid agonists used for anti-diarrhoeal
diphenoxylate
Strong opioid agonists
morphine, methadone, fentanyl, pethidine (meperidine)
Moderate opioid agonists
codeine/dihydrocodeine, tramadol
Main difference between morphine and methadone/fentanyl?
Morphine has weak delta and kappa agonist properties, but methadone and fentanyl has no significant delta and kappa affinity
What is the main difference between methadone and fentanyl?
Methadone is long-acting with a plasma half-life > 24hrs, while fentanyl is short-acting and used as an anaesthetic adjuvant
What is a useful application of pethidine (meperidine)?
As an epidural in labour, less likely to remain in neonate due to its shorter duration of action than morphine, especially in neonates
What are some side effects of pethidine?
- Hallucinogenic and convulsant effects at high dose: N-demethylated in the liver to norpethidine
- Restlessness rather than sedation
- Antimuscarinic ie. parasympatholytic: dry mouth, blurring of vision but no miosis and less spasm of smooth muscle
Contraindication (age group) of opioids
Infants
What is an ADR of opioids that gets better with repeated or chronic use?
n/v
What is an ADR of opioids that develops with repeated or chronic use?
constipation, due to reduced GI motility
What is a diagnostic feature of opioid overdose?
Pinpoint pupils, due to actions in the oculomotor nucleus
CI for morphine (or just used in caution)
asthmatics
- can trigger histamine release from mast cells, causing bronchoconstriction
ADR of opioids
n/v, constipation, drowsiness
miosis, mydriasis (following hypocia)
urinary retention, postural hypotension and bradycardia, immunosuppressant with LT used
(morphine-specific) urticaria and itching, bronchoconstriction, hypotension
Examples of opioid antagonists
naloxone, naltrexone, nalmefene
CI of opioid antagonists (or use with extreme caution)
pt with opiate dependency, they can precipitate potentially fatal withdrawal smx
Opioid analgesia MOA
plays on endogenous mechanism
- inhibit propagation of pain signals
- alter emotional perception of pain
- elevate the pain threshold?
Sites of opioid receptors regulating pain (3)
- peripheral nociceptive terminals
- spine
- brain
