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Psychostimulants

Psychostimulants. Lesson 19. Psychostimulants. Cocaine alkaloid from coca plant Amphetamines (synthetics) similar fx & mechanisms all related to ephedrine (ephedra) dl -amphetamine: methamphetamine MDMA (Ecstasy) ~. Cocaine: Local Anesthetic. Pharmacokinetics Inject SC

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Psychostimulants

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  1. Psychostimulants Lesson 19

  2. Psychostimulants • Cocaine • alkaloid from coca plant • Amphetamines (synthetics) • similar fx & mechanisms • all related to ephedrine (ephedra) • dl-amphetamine: • methamphetamine • MDMA (Ecstasy) ~

  3. Cocaine: Local Anesthetic • Pharmacokinetics • Inject SC • Half-life: 1 hr • Numbing < 2 min • Peak effects: 15-20 minutes • Pharmacodynamics • Blocks Na+ channels • Constricts blood vessels ~

  4. Cocaine: Psychostimulant • Pharmacokinetics • p.o. • ineffective for cocaine • effective for amphetamine analogs • onset: 30 minutes / peak 2-3 hrs • Intranasal • onset 3-4 minutes • peak effects: 15-20 minutes ~

  5. CocainePharmacokinetics • Inhalation (smoking) & IV injection • Onset: < 2 min • For both routes • Euphoria  Crash  Craving • Powerful positive RFT • short delay • high magnitude ~

  6. Pharmacokinetics: Metabolism • Cocaine • By cholinesterases • Blood & Liver • Half-life:  1 hr • Amphetamines • In liver, much excreted unchanged • Half-life: 7-30 hrs ~

  7. Psychostimulant Pharmacokinetics • Tachyphylaxis • brief & transient tolerance • reuse within minutes - hours • Tolerance • Lower doses • Sensitization • repeated use over days ~

  8. Psychostimulant Pharmacology • Indirect agonists: • DA, NE, 5-HT • DA - reinforcing effects • in nucleus accumbens • Euphoria • Rate of change of blood levels • Amphetamine • Primary effects on reuptake • Also  NT &  MAO function ~

  9. Physiological Effects • Sympathomimetic • Heart • Low doses: decrease HR • Moderate:  HR & BP • High: cardiac arrhythmia, failure • Body temperature • Low doses: decrease • moderate & high: increase ~

  10. Physiological Effects • Restlessness • Sleep: interferes with REM • Vomiting • Breathing is facilitated • Depresses cortical activity ~

  11. Psychostimulant Neurotoxicity • DA neurotoxicity;  DA transporters • amphetamine • methamphetamine • 5-HT neurotoxicity • methamphetamine • MDA • MDMA (Ecstasy) • Single high dose ~

  12. Psychotomimetic Effects • Prolonged use • Schizophrenia-like psychosis • Paranoia • Hallucinations: parasitosis • delusions • Methamphetamine • earlier developing • may persist for days, weeks ~

  13. Lethality • Cocaine • Oral: 500 mg • Nasal: 150-300 mg • Amphetamine/Methamphetamine • toxic effects: 15 mg in novices • lethal 500-1700 mg • Inhalation (smoked): much lower ~

  14. Cocaine Abstinence Syndrome Phase 1: Crash 9 hrs - 4 days Phase 2: Withdrawal 1 - 10 weeks Phase 3: Extinction indefinite • Early • Agitation • Depression • Anorexia • High Craving • Middle • Depression • Fatigue • Insomnia • No craving • Late • Exhaustion • Hypersomnolence • Hyperphagia • No Craving • Early • Normal sleep • Normal mood • Low anxiety • Low craving • Middle & Late • Anhedonia • Anergia • Anxiety • High Craving & • conditioned cues • Normal hedonic • response • Normal mood • Episodic craving • Conditioned cues • trigger craving Binge Abstinence Relapse Gawin & Kleber (1986)

  15. Cocaine Abuse: Animals • Self-administration • Will work hard to get • progressive FR6400 • Continuous access: • Weight loss • Self-mutilation • parasitosis? • Death within 2 weeks ~

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