Opioid Analgesics 2
Terms
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- Morphine
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Mechanism: mu opioid receptor opens K and less Ca -> adenylate cyclase inhibition -> reduced transmitter release
Dorsal horn has opioid receptors that gate nociceptive input (these receptors receive input from 5-HT and NE)
Clinical Use: analgesia without loss of consciousness, continuous dull pain better relieved than sharp intermittent, cough suppression
Side Effects: prominent physical dependence (less severe than ethanol, barbiturates, and some BDZs), cross tolerance
respiratory depression (even low dose), resulting BP fall, constriction of pupils (miosis) useful for abuse diagnosis, hypotension only in hypovolemic patients, nausea, constipation, epigastric pain, and micturition -
Naloxone
Naltrexone -
Repeated injections of small dose of this opiate receptor antagonist.
May precipitate withdrawal in those who are dependent.
Naloxone given i.v.
Naltrexone, longer T1/2, orally given - NSAIDs + opiates
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analgesic effects are additive
in some situations NSAIDs may be more analgesic - Codeine
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Mechanism: methylated morphine, demethylated into morphine
Clinical Use: analgesic, cough suppressant -
Hydromorphone
Oxymorphone - identical to morphine but more potent
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Oxycodone
Hydrocodone -
Mechanism: equipotent and better absorbed than morphine
Clinical Use: anti-tussive, analgesic-antipyretic mixtures - Heroin
- Mechanism: acetylated morphine, deacetylated to morphine, high lipid solubility so rapid penetration through BBB
- Miperidine
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Mechanism: shorter duration of action than morphone
Clinical Use: obstetrical analgesia; less spasmogenic, less constipation/micturition, and less respitory depression than morphine - Diphenoxylate
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Mechanism: insoluble -> little abuse potential, no CNS effect at therapeutic dose
Clinical Use: diarrhea treatment in combo w/ atropine - Fentanyl
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80x more potent than morphine
patch for cancer patients - Methadone
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Mechanism: better bioavailability than morphine, longer T1/2, less withdrawal
Clinical Use: superior to morphine, moderate to sever pain, replacement therapy for opiate addiction - Propoxyphene
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less effective than codeine
mild to moderate pain
less abuse liability than codeine - Pentazocin
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Mechanism: partial my agonist, powerful kappa agonist, 1/2 to 1/5 as potent
Clinical Use: analgesic
Side Effects: less respiratory depression, higher dysmorphic effect (anxiety, nightmares, hallucination), increase BP and HR - Clonidine
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reduce acute phase of opiate withdrawal symptioms
also reduce psychological craving