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 Difference is potency compare to morphine = 1 ~

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 ~

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 ~

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 ~

Opiate Effects Analgesia Euphoria Respiratory Depression Narcosis drowsiness ~

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

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 ~

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

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 ~

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

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

Nucleus Accumbens VTA Opioid - GABA - DA

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

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

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 ~

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 ~