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Opiates

Opiates. Lesson 17. Opiates. Alkaloids from opium poppy Opium extract 0.5% codiene 20% morphine alter structure  heroin Opioids: synthetic analogs (texts) Major effects: Analgesia & Euphoria ~. Opiate Family. Large family of drugs neuropeptides morphine is prototype

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Opiates

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  1. Opiates Lesson 17

  2. Opiates • Alkaloids • from opium poppy • Opium extract • 0.5% codiene • 20% morphine • alter structure  heroin • Opioids: synthetic analogs (texts) • Major effects: Analgesia & Euphoria ~

  3. Opiate Family • Large family of drugs • neuropeptides • morphine is prototype • Difference is potency • compare to morphine = 1 ~

  4. Relative Potency Opiate Potency Morphine 1 Methadone 1 Propoxyphene (Darvon) .05 Codeine .1 Meperidine (Demerol) .1 Oxycodone (Oxycontin, Percodan) .75 Heroin 3-4 Fentanyl 80 ~

  5. Pharmacokinetics • Route: sc, im, iv • p.o. not as effective • ion trapping • 1st pass metabolism • Significant brain levels: 30-60 min • immediate euphoria? • Conditioned effects ~

  6. Pharmacokinetics • Half-life: about 3 hrs • Duration of effects: 4-5 hrs • then withdrawal begins • Heroin: crosses BBB more easily • diacetylmorphine • biotransformed into morphine • Codiene: • 10% transformed to morphine ~

  7. Opiate Effects • Analgesia • Euphoria • Respiratory Depression • Narcosis • drowsiness ~

  8. Opiate Effects • Antitussive • inhibits coughing • Constipation • Impotence & reduced libido • Reduced aggression & social interaction • opioid role in social bonds • Alters food intake, BT, etc. ~

  9. Opioid Receptors • Areas Mapped (1970s) • Pain Pathways: • Periaqueductal Gray (PAG), • Dorsal Horn Spinal Cord • Also: • Hypothalamus • G. I. Tract, • Limbic System (VTA, Nucleus Accumbens) • Medulla ~

  10. Opioid Receptors • 2d messenger systems • Open K+ channels • hyperpolarization • Close Ca++ channels • decreased NT release • Inhibits adenylyl cyclase •  cAMP ~

  11. Opioid Receptors: Subtypes • m(mu) • m1 –  supraspinal & spinal analgesia • m2 –  respiration,  HR, euphoria • d (delta) • Modulates m analgesia, positive RFT • k (kappa) • spinal analgesia, pain perception • sedation, dysphoria, hallucinations • gut motility, body temperature ~

  12. Endorphins • Peptide Family: • Hormones, Neuromodulators & NTs • b -Endorphin • Met- & Leu-Enkephalin • Dynorphin ~

  13. Euphoria & Reward • Ventral Tegmental Area (VTA) • opioid neurons • dopamine neurons • GABA neurons? • hypothesized • GABA inhibits DA neurons • Opioids inhibit GABA neurons ~

  14. Opioid - GABA - VTA Nucleus Accumbens DA

  15. Other Opioid-Mediated Behaviors • Social Bond Formation • Various abnormal behaviors • Schizophrenia • Infantile Autism • Self-Mutilation ~

  16. Opiate Problems • High Dependence Liability • Positive & Negative Reinforcer • Withdrawal Symptoms • Tolerance & Cross Tolerance • Different rates for various effects • Euphoria: fast • Respiratory depression: slow ~

  17. Opiate Dependence: Treatment • 2007 National Survey on Drug Use and Health: heroin use / oxycodone • past year: 366, 000 / 1.4 million • past month 153,000 / 369,000 • Methadone Treatment • taken p.o. • half-life about 36 hrs •  euphoria & blocks withdrawal • develop methadone dependence ~

  18. Opiate Dependence: Treatment • LAAM: L-alpha-acetylmethadol • (Orlaam) • half-life 2-6 days • slightly more treatment dropouts • not recommended for women of child-bearing age • *Buprenorphine (Subutex) •  craving • *Buprenorphine + naloxone (Suboxone) •  craving & rewarding effects ~

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