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Central Institute of Psychiatry - 9 July 2022
Pharmacology
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Class 2 antipsychotic drugs act as?

Appeared in: Central Institute of Psychiatry - 9 July 2022

Explanation

  • Typical (Class 2) antipsychotics are defined by their primary mechanism of action: antagonism of dopamine D2 receptors.
  • This blockade is highly correlated with their antipsychotic potency.
  • The therapeutic effect, particularly on positive symptoms (e.g., hallucinations, delusions), is attributed to D2 receptor blockade in the mesolimbic pathway of the brain.
  • While some older agents also have effects on other receptors, D2 antagonism is their core and defining feature.

Why Other Options Were Wrong

  • Option A: This is not the primary mechanism. While many atypical (second-generation) antipsychotics are potent serotonin (5-HT2A) receptor antagonists, typical antipsychotics' main action is on dopamine receptors. Also, they act as antagonists, not 'inhibitors' of serotonin.
  • Option C: Antagonism of epinephrine (adrenergic) receptors is not the primary antipsychotic mechanism. It is associated with side effects like orthostatic hypotension seen with some antipsychotics (e.g., chlorpromazine), but it does not treat psychosis.
  • Option D: Antagonism of acetylcholine (muscarinic) receptors is a side effect profile of some low-potency typical antipsychotics (like chlorpromazine), leading to anticholinergic effects (dry mouth, blurred vision, constipation). It is not their therapeutic mechanism for psychosis.

Related Visual

Visual explanation — Related Visual
Clinical Relevance
  • Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mechanism of action of typical (Class 2) antipsychotic drugs as background academic context rather than a clinical decision trigger.
  • A crucial nursing responsibility is monitoring for Extrapyramidal Symptoms (EPS) using tools like the Abnormal Involuntary Movement Scale (AIMS). Early detection and reporting are vital.
  • Nurses should educate patients about potential side effects like hyperprolactinemia (e.g., breast tenderness, menstrual changes) and the importance of not stopping medication abruptly.
  • What if? If a patient on a typical antipsychotic develops a high fever, severe muscle rigidity, and altered mental status, the nurse must suspect Neuroleptic Malignant Syndrome (NMS), a life-threatening emergency, and notify the physician immediately.
How to Approach the Question
  • First, identify the core of the question: it asks for the mechanism of 'Class 2 antipsychotic drugs'. Recognize that 'Class 2' refers to typical or first-generation antipsychotics.
  • Recall the primary pharmacological action of this drug class. The defining feature of typical antipsychotics is their effect on the dopamine system.
  • Evaluate the options. 'Dopamine Antagonist' directly describes this primary mechanism.
  • Consider the other options. Serotonin effects are more related to atypical antipsychotics, while epinephrine and acetylcholine antagonism are primarily associated with side effect profiles, not the main therapeutic action.
Concept Tested & Keywords
  • Concept Tested: Mechanism of action of typical (Class 2) antipsychotic drugs
  • Stem keywords: Class 2 antipsychotic drugs, act as
  • Lead-in keywords: BEST, MOST RELEVANT CLUE
  • Negative lead-in flag: false

Question ID

Q_F8ead-8i69aaHFKS3uqz

Reference Book

E6 Robert Boland, Marcia L. Verduin - Kaplan and Sadock's Comprehensive Text of Psychiatry-Wolters Kluwer Health (2024) (pp 1-16525 of 16525) pp. 9864-9866, 9880-9882, 9926-9928

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