1. CNS effects of opioid agonists
    analgesia, euphoria, sedation/drowsiness, repiratory depression, miosis, nausea/vomiting, antitussive
  2. GI effects of opioid agonists
    • increase resting tone of stomach, decrease motility, delay emptying time
    • constipation - longitudinal muscle relaxation, circular muscle contraction
    • spasm in biliary smooth muscle - opioids contraindicated if pt has gallstones
    • other smooth muscle: increase tone and contraction, spasm of urinary tract
  3. Neuroendocrine effects
    • act in hypothalamus to inhibit GnRH and CRH, decreasing plasma concentrations of LH, FSH, ACTH, and β-endorphin.
    • release anti-diuretic hormone (ADH) - can lead to urinary retention.
  4. morphine (hydromorphone, oxymorphone, levorphanol)
    • strong µ agonist for analgesia
    • poorly absorbed after oral administration due to significant first-pass effect - given SC, IM, or IV - peak at 1.5hr, last 4hr
    • Adverse rxn: shouldn't be taken w/ MAO I
    • OD: pinpoint pupils, respiratory depression and coma
  5. codeine (hydrocodone, oxycodone)
    • moderate pain, cough
    • similar duration of action as morphine
    • 5-15% is converted to morphine
    • good oral efficacy
    • SE: constipation, nausea, itching, vomiting, drowsiness, dry mouth, urinary retention
  6. heroin
    • strong µ agonist
    • heroin is diacetylmorphine: very lipophilic and rapidly enters the brain, but shorter half-life
  7. levophanol
    • strong µ agonist
    • similar to morphine w/ less nausea, vomiting
    • half life: 12-16h
  8. Meperidine
    • strong µ agonist (no longer @ UCLA)
    • antimuscarinic activity, less contraction of spincter of Oddi
    • half life: 3h, metab half life: 15-20h
    • MAO I - fatal interaction
  9. fentanyl
    • strong µ, K agonist
    • 80x more potent than morphine, lipophilic
    • also avail. transdermal patches
  10. diphenoxylate (lomotil)
    • treatment of diarrhea
    • insoluble, remains in the gut
    • atropine is added to prevent abuse
  11. loperamide
    • immodium
    • constipating effect
    • substrate for p-glycoprotein, so it won't accumulate in the brain
  12. methadone
    • strong µ agonist
    • longer duration of action, good oral bioavailability
  13. propoxyphene (Darvon)
    • very weak analgesic, ASA may be more effective
    • removed from market 2010
  14. tramadol (Ultram)
    • synthetic codeine, weak agonist
    • inhibition of uptake of NE, 5HT
    • as effective as morphine for mild to moderate pain
  15. pentazocine (Talwin)
    • acts as a weak antagonist in the presence of µ agonists
    • acts as a partial agonist at the µ receptor
    • has κ agonist activity
    • PO, less potent than morphine
    • can produce dysphoria, anxiety; less vomiting than morphine
    • less abuse potential
  16. buprenorphine
    • partial agonist
    • moderate to severe pain
    • sublingual administration
    • more potent than morphine @ low doses
    • alternative to methadone
    • slow dissociation from receptors
  17. naloxone
    • opioid antagonist, treatment of overdose
    • SC, IM, IV - poor oral bioavail, short half life!
  18. naltrexone
    • opioid antagonist
    • similar to naloxone - more potent, longer acting
    • can be taken PO
  19. dextromethorphan
    • centrally acting antitussive
    • no analgesic, sedative, GI activity
    • (codeine can also be used as an antitussive)
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