Chemistry | Structure-Fxn relationships that were relied upon in the past have become less important |
| | Instead, receptor-fxn relationships and functional assays are more clinically relevant |
✽ Classification According to Potency ✽ |
Low Potency | Chlorpromazine |
| | Thioridazine |
Medium Potency | Loxapine |
| | Perphenazine |
High Potency | Haloperidol |
| | Droperidol |
| | Fluphenazine |
| | Pimozide |
✽ MOA ✽ |
Block dopamine D2 receptors | D2 receptor binding affinity (but not D1) strongly correlates with clinical potency of typical antipsychotic agents |
Blockade of postsynaptic D2 receptors | ⇨ Reduction of dopaminergic neurotransmission |
D2 receptor blockade in ALL dopaminergic pathways | ⇨ beneficial in the mesolimbic pathway |
| | ⇨ alleviates positive sx of SZ |
| | ⇨ It doesn't do really anything for the negative or cognitive sx |
| | Side Effects: |
| | • D2 receptor blockade in nigrostriatal pathway ⇨ extrapyramidal sx (EPS) |
| | • D2 receptor blockade in the tuberoinfundibular pathway ⇨ increased prolactin release from the anterior pituitary |
Blocks other receptors: |
5-HT2A blockade | Contributes to antipsychotic effects |
Other receptor blockade | Numerous additional side effect |
✽ SIDE EFFECTS ✽ |
EPS | Various movement disorders associated with antipsychotic therapy (occurs mostly with 1st gen) |
| | Occurs due to D2 receptor blockade in the nigrostriatal pathway |
| | • Akathisia: uncontrollable motor restlessness |
| | • Dystonias: muscular spasms of the neck, eyes, and tongue |
| | • Drug-Induced Parkinson's Syndrome: Resembles Parkinson's Syndrome |
| | • Tardive Dyskinesia (TD): occurs after months or years of tx; may become irreversible; repetitive, involuntary, purposeless movements (typically facial muscles are involved); mechanism: up-regulation and supersensitivity of D2 receptors (that can become permanent) |
Hyperprolactinemia | D2 receptor blockade in the tuberoinfundibular pathway causes increased plasma prolactin levels (Hyperprolactinemia) |
| | Manifested as: Amenorrhea-galactorrhea in women, gynecomastia in men, Infertility in both men and women |
ADRs caused by Blockade of Non-Dopamine Receptors | 1st generation antipsychotic drugs also block 5-HT-2, alpha 1 adrenergic, muscarinic, and histamine H-1 receptors ⇨ More Side Effects |
Blockade of H1 Receptors | Sedation |
Blockade of alpha 1 adrenergic receptors | Orthostatic hypotension (could result in falls and injuries) |
Blockade of muscarinic receptors | dry mouth, urinary retention, blurred vision, tachycardia, constipation, toxic-confusional state |
Blockade of both H1 and 5-HT-2A receptors | Weight gain |
ADDITIONAL SIDE EFFECTS |
Typical antipsychotic agents affect hypothalamic function | impaired ability to regulate body temperature |
| | Hypo or Hyperthermia may result, depending on the ambient temperature |
Thioridazine | Cardiac toxicity: reflected in prolongation of QTc interval and abnormal configuration of ST segment and T wave (correlates to increased risk of ventricular arrhythmias) |
| | Retinal Tox: (pigmentary retinopathy): decreased vision and "browining" of vision |
Neuroleptic Malignant Syndrome (NMS) | Rare, but life-threatening reaction to antipsychotic drugs |
| | Symptoms: extreme muscle rigidity (lead pipe), hyperreflecia, fever, unstable BP, tachycardia, sweating, rapid changes in mental status, confusion, and coma |
| | Lab: myoglobinemia and metabolic acidosis |
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Good job for the effort, but need to be refined and detailed.
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