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Understanding Schizophrenia: Theories and Treatments

Explore the thought disorder of schizophrenia, its symptoms, theories, and drug treatments. Learn about dopamine and serotonin theories, antipsychotic drugs, and their pharmacological actions.

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Understanding Schizophrenia: Theories and Treatments

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  1. Drugs used in schizophrenia

  2. Schizophrenia - A thought disorder. - Characterized by a divorcement from reality in the mind of the person (psychosis). - It may involve visual and auditory hallucinations, delusions, intense suspicion, feelings of control by external forces (paranoia)

  3. Schizophrenia Positive Symptoms • Hallucinations • Delusions • Paranoia

  4. Negative Symptoms • Social withdrawal • Anhedonia ( absence of pleasure ) • Emotional blunting

  5. Etiology of Schizophrenia structural and functional abnormalities in the brains of schizophrenic patients: 1. Enlarged cerebral ventricles 2. Atrophy of cortical layers 3. Reduced volume of the basal ganglia

  6. THEORIES OF SCHIZOPHRENIA 5-HT theory • assumes serotonin deficiency • based on the observation that LSD produces hallucinations. LSD: (Lysergic Acid Diethyl amide), an ergot derivative synthesized in 1943, which antagonizes some peripheral actions of 5-HT

  7. THEORIES OF SCHIZOPHRENIA 5-HT theory (Cont’d): ❏not accepted : WHY? - No biochemical evidence suggesting reduced 5-HT production in schizophrenia - LSD hallucinations not very similar to schizophrenia ❏ There is now a renewed interest with the action of the atypical antipsychotics, such as clozapine, on 5-HT2 receptors.

  8. THEORIES OF SCHIZOPHRENIA Dopamine theory ❏ Schizophrenia is due to increased dopaminergic activity in the limbic system ❏ This may be due to:  1- Increased sensitivity or number of dopamine receptors  2- Increased synthesis or release of dopamine   3- Reduced enzymatic destruction of dopamine 

  9. THEORIES OF SCHIZOPHRENIA Dopamine theory EVIDENCE FOR THE DOPAMINERGIC INVOLVEMENT IN SCHIZOPHRENIA: • 1- Most antipsychotic drugs block postsynaptic dopamine (D2) receptors in the CNS

  10. THEORIES OF SCHIZOPHRENIA Dopamine theory EVIDENCE FOR THE DOPAMINERGIC INVOLVEMENT IN SCHIZOPHRENIA: : 2- e.g. Levodopa (dopamine precursor) Amphetamine (cause release of endogenous dopamine) Apomorphine (direct dopamine receptor agonist) 2-

  11. THEORIES OF SCHIZOPHRENIA Dopamine theory EVIDENCE FOR THE DOPAMINERGIC INVOLVEMENT IN SCHIZOPHRENIA: • 3- postmortem & brain PET scans show that schizophrenic patients have increased dopamine receptors than normal people.

  12. THEORIES OF SCHIZOPHRENIA • Evidence Against dopamine theory: • - Antipsychotic drugs are only partially effective for most, and ineffective for some patients • -  Several atypical antipsychotic drugs (e.g. clozapine) are effective in schizophrenia in spite of weak effect on D2 receptors

  13. THEORIES OF SCHIZOPHRENIA • Evidence Against dopamine theory: 3- Even with traditional phenothiazines clinical efficacy is more correlated with α1-blocking activity than with dopamine blocking activity

  14. Dopamine System • Dopaminergic pathways in the brain : • Mesolimbic - mesocortical pathway (behavior) • Nigrostriatal pathway (co-ordination of voluntary movements) • Tuberoinfundibular pathway (endocrine effects) • Medullary - periventricular pathway (metabolic effects)

  15. THE DOPAMINERGIC SYSTEM

  16. Tyrosine Dopamine Synapse Tyrosine L-DOPA DA

  17. Dopamine Receptors • at least five subtypes of receptors: D 1, D 2, D 3, D 4, D 5

  18. Antipsychotic drugs act on : Dopamine receptors α1 - adrenoceptors   Muscarinic    H1 – histaminic    Serotonergic (5-HT2)

  19. Classification of Antipsychotic drugs A) Typical Antipsychotic Drugs According to chemical structure into : • Phenothiazine derivatives : • Chlorpromazine Thioridazine • Butyrophenones • Haloperidol • Thioxanthene Thiothixene

  20. B) Atypical Antipsychotic Drugs • Dibenzodiazepines Clozapine • Benzisoxazoles Risperidone • Thienobenzodiazepines Olanzapine • Dibenzothiazepines Quetiapine

  21. Mechanism of Antipsychotic Action

  22. Atypical drugs exert their antipsychotic action through blocking serotonin ( 5HT2) & dopamine receptors.

  23. Pharmacological Actions • C.N.S : Antipsychotic effect : • Produce emotional quieting • psychomotor slowing • Decreases hallucinations Mechanism: Blockade of dopamine receptors in the mesolimbic system.

  24. Pharmacological actions ( con.) Extrapyramidal Symptoms Abnormal involuntary movements such as tremors, parkinsonism & tardivedyskinesia Mechanism : Blockade of dopamine receptors in the nigrostriatum system

  25. Endocrine effects Galactorrhea, amenorrhea, gynecomastia & impotence ( hyperprolactinemia). Mechanism : Prevent inhibiting effect of dopamine on prolactin release from pituitary gland (blocking dopamine receptors intuberoinfundibular system)

  26. Pharmacological Actions ( cont.) Metabolic effects Changes in eating behavior and weight gain Mechanism Blockade of dopamine receptors in the medullary – periventricular pathway

  27. Pharmacological Actions ( cont.) Anti-emetic effect Effective against drug & disease- induced vomiting ( not- motion sickness) Mechanism : Blockade of dopamine receptors in the CRTZ of the medulla

  28. Pharmacological Actions ( con.) A.N.S Anticholinergic Effects - Blurred vision - Dry mouth - Urinary retention - Constipation Mechanism Blockade of muscarinic receptors

  29. Continue on A.N.S Antiadrenergic Effects - Postural hypotension - Impotence - Failure of ejaculation Mechanism : Blockade of α- adrenergic receptors

  30. Pharmacological Actions ( con.) Other Actions : Temperature regulation Mau cause lowering of body temperature Mechanism : Heat loss as a result of vasodilation ( α- blocking ) Or due to central effect

  31. Other Actions ( con.) ECG changes Prolongation of QT interval Abnormal configuration of ST- segment & T wave. Antihistaminic effect Sedation due to H1receptor blockade

  32. Therapeutic USES PSYCHIATRIC • Schizophrenia ( primary indication) • Acute mania • Manic-depressive illness • Senile dementia

  33. ADVERSE EFFECTS C.N.S . Sedation, drowsiness, fatigue haloperidol , Risperidone Extrapyramidal symptoms : Occurring earlyin the treatment as : Parkinson,s syndrome

  34. occurring late in the treatment as : Tardive Dyskinesia & Neuroleptic Malignant Syndrome

  35. Tardive Dyskinesia: (from Latin tardus, slow or late coming) it is a disorder of involuntary movements (choreoathetoid movements of lips, tongue, face, jaws, and of limbs and sometimes trunk).

  36. -older women treated for long periods are the most susceptible although it can happen at any age or sex in 20-40% of chronic patients treated with antipsychotics - Early recognition is important as advanced cases are difficult to reverse.

  37. TREATMENT: i) Decrease dopamine receptor sensitivity by discontinuing the antipsychotic drug or at least reducing the dose ii) Eliminate all drugs with central anticholinergic action such as antiparkinsonism, antidepressants

  38. iii) If the above two steps fail to bring improvement, add diazepam which may help by enhancing GABA activity

  39. - Neuroleptic Malignant Syndrome: ♦ Rare but life threatening. ♦ Symptoms are muscle rigidity and high fever ( clinically similar to anaesthetic malignant hyperthermia ). ♦ The stress leukocytosis and high fever associated with this syndrome may wrongly suggest an infection.

  40. ♦ Mechanism could be due to oversensitivity to the blockade of postsynaptic dopamine receptors. ♦ Treatment of this syndrome includes dantroline, dopamine agonists such as bromocriptine, muscle relaxants such as diazepam and anticholinergic drugs e.g. procyclidine

  41. Adverse effects ( Continue ) . A. N. S Antiadrenergic Effects: - Postural hypotension - Impotence - Failure of ejaculation Chlorpromazine

  42. Adverse Effects ( con.) Endocrine side effects ( Hyperprolactinemia )

  43. MISCELLANEOUS SIDE EFFECTS Agranulocytosis: clozapine (about 1-2%) usually happen after 6-18 weeks.   Weekly CBC is mandatory Ventricular arrhythmias Thioridazine

  44. Miscellaneous Adverse Effects ( con.) • Obstrucive jaundice • Granular deposits in cornea • Retinal deposits ( thioridazine) • Weight gain

  45. Continue -Seizures Clozapine

  46. PHARMACOKINETICS • Incompletely absorbed • Highly lipid soluble • Highly bound to plasma proteins • Undergo extensive first-pass hepatic metabolism. • Excretion by the kidney

  47. Pharmacokinetics ❏Thioridazine & Haloperidol Have Active metabolites ❏The metabolite of thioridazine, mesoridazine, is more potent than the parent compound and accounts for most of the therapeutic effect.

  48. Atypical Antipsychotics • Effective in treatment of resistant schizophrenia • Are considered to be first line treatments for schizophrenia • Little or no extrapyramidal side effects (great affinity on D1,D4 more than D2 in limbic system )

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