DSSSB - 28 August 2019 (Shift-1)
Pharmacology
Easy
What is the main action expected of tricyclic antidepressants?
Appeared in: DSSSB - 28 August 2019 (Shift-1)
Explanation
- Tricyclic antidepressants (TCAs) primarily function by inhibiting the reuptake of key neurotransmitters, specifically norepinephrine and serotonin, at the presynaptic neuron.
- This blockade occurs at the transporter proteins (NET and SERT) located on the presynaptic membrane, leading to an increased concentration of these neurotransmitters in the synaptic cleft.
- By increasing the availability of norepinephrine (a catecholamine) and serotonin, TCAs enhance neurotransmission, which is the basis for their antidepressant effect.
- Among the given choices, 'Blocking presynaptic receptors of catecholamine' is the closest description, as the action site is presynaptic and the target neurotransmitter class is correct, despite the imprecise use of 'receptor' for a 'transporter'.
Why Other Options Were Wrong
- Option B: TCAs have a very weak effect on dopamine reuptake and do not primarily block dopamine receptors. Antipsychotic medications are the class that primarily blocks dopamine receptors.
- Option C: TCAs do not have a significant effect on Gamma-Aminobutyric Acid (GABA) receptors. Drugs that act on GABA receptors are typically used as anxiolytics, sedatives, or anticonvulsants.
- Option D: TCAs do not block the postsynaptic receptors for norepinephrine as their primary therapeutic action. Instead, by blocking reuptake, they increase the amount of norepinephrine available to stimulate these receptors. Blockade of certain adrenergic receptors (alpha-1) does occur, but this contributes to side effects like orthostatic hypotension, not the antidepressant effect.
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 Tricyclic Antidepressants (TCAs) as background academic context rather than a clinical decision trigger.
- Nurses must monitor patients on TCAs for a wide range of side effects due to their action on other receptors, including anticholinergic effects (dry mouth, constipation, urinary retention), antihistaminic effects (sedation, weight gain), and alpha-1 adrenergic blockade (orthostatic hypotension).
- A critical safety concern with TCAs is their high toxicity in overdose, which can lead to life-threatening cardiac arrhythmias due to sodium channel blockade. Patient education on adhering to the prescribed dose is vital.
- What if? If a patient presents with severe depression and a history of recent myocardial infarction, a TCA would likely be contraindicated due to its cardiac risks. A more selective agent, like an SSRI, which has a much safer cardiovascular profile, would be the preferred choice.
How to Approach the Question
- First, identify the core of the question: it asks for the 'main action' of a specific drug class, Tricyclic Antidepressants (TCAs).
- This is a factual recall question from pharmacology. Access your knowledge about the mechanism of major antidepressant classes.
- Recall that TCAs are functionally known as norepinephrine and serotonin reuptake inhibitors.
- Analyze the options. The key action is 'reuptake inhibition' which occurs at the 'presynaptic' terminal.
- Evaluate each option against this mechanism. Option A mentions 'presynaptic' and 'catecholamine' (which includes norepinephrine). Option D mentions 'blocking receptors,' which is incorrect for the main therapeutic action. Options B and C involve the wrong neurotransmitter systems.
- Select the option that best, even if imperfectly, describes the known mechanism. Here, the presynaptic location is the key differentiator, making Option A the most plausible choice.
Concept Tested & Keywords
- Concept Tested: Mechanism of action of Tricyclic Antidepressants (TCAs)
- Stem keywords: tricyclic antidepressants, main action
- Lead-in keywords: What is
- Negative lead-in flag: false
Question ID
Q8LcF7zOpuJlCOfWxT2XXR
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. 10236-10238, 10237-10239
E6 Pharmacology Katzung 16e p. 848-850
Practise the full DSSSB - 28 August 2019 (Shift-1)
Attempt every question from this paper in a timed mock, then review the full solution for each one.
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