Neuroleptics

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21 Terms

1
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Neuroleptics

  • drugs used in management of psychosis

  • antipsychotics

  • divided into typical and atypical agents

    • typical: older

    • atypical: newer, fewer extrapyramidal effects

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Dopamine hypothesis

schizophrenia is caused by increased and dysregulated levels of DA neurotransmission in brain

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Dopamine pathway functions

  • reward (motivation)

  • pleasure/euphoria

  • motor function (fine tuning)

  • compulsion

  • perseveration

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Serotonin pathway functions

  • mood

  • memory processing

  • sleep cognition

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Types of Dopamine receptors

  • D1 receptor family

    • promote cAMP

    • promote PIP2 hydrolysis

  • D2 receptor family

    • decrease cAMP

    • increase K+ currents

    • decrease voltage-gated Ca2+ currents

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Typical antipsychotics

  • D2 receptor antagonists

  • haloperidol (high potency)

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MOA of typical antipsychotics

  • block D2 receptors in all of the CNS dopaminergic pathways

    • prevent dopamine being used

    • reduce dopamine

  • antagonism of mesolimbic, and possibly mesocortical, D2 receptors

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Tardive Dyskinesia

  • side effect of antipsychotics

  • observed most frequenty after prolonged treatment with drugs that have a high affinity for D2 receptor, like haloperidol

  • repetitive, involuntary, stereotyped movements of facial musculature, arms, trunk

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Neuroleptic malignant syndrome (NMS)

  • most severe adverse effect of the typical antipsychotics

  • rare but life-threatening

  • catatonia, stupor, fever, autonomic instability, myoglobinemia

  • death occur in about 10% of cases

  • most commonly associated with typical antipsychotic drugs that have a high affinity for D2 receptors, like haloperidol

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Atypical psychotics

  • D2 receptor antagonists (low potency)

  • Clozapine

  • Olanzapine

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MOA of atypical antipsychotics

  • relatively low affinity for D2 receptors

  • antagonist action at both 5-HT2 and D2 receptors

  • rapid D2 dissociation

  • 5-HT11A agonism

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5-HT2 hypothesis

antagonist action at the serotonin 5-HT2 receptor or antagonist action at both 5-HT2 and D2 receptors is critical for the antipsychotic effect of atypical antipsychotics

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Side effects of atypical antipsychotics

  • significantly milder extrapyramidal symptoms than typical antipsychotics

  • higher incidence of metabolic dysfunction, weight gain, sedation

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Parkinson’s disease

  • selective loss of dopaminergic neurons in substantia nigra pars compacta

    • at least 70% neurons destroyed when symptoms appear

  • results in bradykinesia (slow movement), rigidity, impaired postural balance

  • characteristic tremor when limbs at rest

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Why is carbidopa administered with levodopa for parkinson’s disease treatment?

carbidopa is an AADC inhibitor that blocks the peripheral metabolism of levo-dopa, allowing more levo-dopa in the brain that can be converted into dopamine

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what enzymes metabolize L-Dopa in PNS?

  • aromatic l-amino acid decarboxylase (AADC)

  • catechol-o-methyltransferase (COMT)

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Can carbidopa cross the blood-brain barrier?

No

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How do entacapone and tolcapone increase the fraction of levodopa available to the brain?

  • inhibit COMT in periphery

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What enzyme transports L-DOPA across the blood-brain barrier?

L-neutral amino acid transporter (LNAA)

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What metabolizes L-DOPA to dopamine in the brain?

AADC

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Major limitation to use of dopamine receptor agonists

  • tendency to induce unwanted adverse effects (nausea, peripheral edema, hypotension)

  • may produce excessive sedation, vivid dreams, hallucinations (esp in elderly)

  • may also impair impulse control (gambling, overspending, compulsive eating)