Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs

Question 631: Cholinomimetic is not used for:

A. Cobra bite
B. Myasthenia gravis
C. Open angle glaucoma
D. Bradycardia (Correct Answer)

Explanation: ***Bradycardia*** - **Cholinomimetics** generally cause **bradycardia** (slowing of heart rate) due to their parasympathomimetic effects. Therefore, they are contraindicated in cases of existing bradycardia. - Using them in a patient with bradycardia would further decrease heart rate, potentially leading to adverse cardiovascular events. *Open angle glaucoma* - **Cholinomimetics** (e.g., pilocarpine) are used in open-angle glaucoma to cause **miosis** (pupil constriction) and **ciliary muscle contraction**. - This action increases the outflow of **aqueous humor** through the trabecular meshwork, thus reducing intraocular pressure. *Cobra bite* - **Neurotoxic snake venoms**, such as from a cobra, contain toxins that block acetylcholine receptors at the **neuromuscular junction**. - **Cholinomimetics** (specifically acetylcholinesterase inhibitors like neostigmine) can be used as an adjunct treatment to overcome this block by increasing the concentration of acetylcholine in the synaptic cleft. *Myasthenia gravis* - **Myasthenia gravis** is an autoimmune disease where antibodies block or destroy **nicotinic acetylcholine receptors** at the neuromuscular junction, leading to muscle weakness. - **Cholinomimetics** (specifically acetylcholinesterase inhibitors like pyridostigmine) are a cornerstone of treatment as they increase the amount of acetylcholine available to bind to the remaining functional receptors, improving muscle strength.

Question 632: The H3 receptor agonist exhibits all of the following actions except:

A. Inhibition of H1 mediated bronchoconstriction
B. Negative chronotropic effect on atria
C. Inhibition of H1 receptors induced wakefulness
D. Increase in H2 mediated gastric secretion (Correct Answer)

Explanation: ***Increase in H2 mediated gastric secretion*** - H3 receptor agonists inhibit the release of **histamine** from presynaptic terminals. - Less histamine means **reduced stimulation of parietal cells** (which are H2-mediated) and a decrease, not an increase, in gastric acid secretion. - H3 agonists would therefore **reduce, not increase**, H2-mediated gastric secretion. *Inhibition of H1 receptors induced wakefulness* - H3 receptor agonists reduce the release of histamine from histaminergic neurons, leading to **decreased H1 receptor activation** in the brain. - This diminished H1 activation contributes to a **reduction in wakefulness** and promotion of sleep. - This is a **true action** of H3 agonists. *Inhibition of H1 mediated bronchoconstriction* - By decreasing histamine release, H3 receptor agonists lower the amount of histamine available to bind to H1 receptors on **bronchial smooth muscle**. - This results in a **reduction in H1-mediated bronchoconstriction**. - This is a **true action** of H3 agonists. *Negative chronotropic effect on atria* - H3 receptors are present in the heart, and their activation can lead to a **reduction in heart rate** (negative chronotropic effect). - This effect is mediated through the **inhibition of histamine release locally** or directly on cardiac cells. - This is a **true action** of H3 agonists.

Question 633: Which of the following drugs is not used for the treatment of overactive bladder?

A. Oxybutynin
B. Flavoxate
C. Duloxetine (Correct Answer)
D. Darifenacin

Explanation: ***Duloxetine*** - **Duloxetine** is a **serotonin-norepinephrine reuptake inhibitor (SNRI)** primarily used to treat major depressive disorder, generalized anxiety disorder, neuropathic pain, and **stress urinary incontinence (SUI)** [3]. - While it affects neurotransmitters involved in bladder control, its primary indication is SUI through increasing urethral sphincter tone, not directly treating the urgency and frequency associated with **overactive bladder (OAB)** [3]. *Darifenacin* - **Darifenacin** is a **M3 muscarinic receptor antagonist** that selectively targets receptors in the bladder, reducing detrusor muscle contractions [1]. - This action helps to alleviate symptoms of urgency, frequency, and urge incontinence characteristic of **overactive bladder (OAB)** [1]. *Oxybutynin* - **Oxybutynin** is a **non-selective muscarinic receptor antagonist** that relaxes the detrusor muscle of the bladder, decreasing bladder contractility [1], [2]. - It is a long-standing and commonly used medication for managing the symptoms of **overactive bladder (OAB)** and neurogenic bladder [2]. *Flavoxate* - **Flavoxate** is a **direct relaxant of smooth muscle** in the urinary tract, and it has mild anticholinergic, local anesthetic, and analgesic properties. - It is used to relieve symptoms like dysuria, urgency, and nocturia associated with various urinary tract conditions including **overactive bladder (OAB)** and interstitial cystitis.

Question 634: Which of the following is not a carbamate?

A. Physostigmine
B. Neostigmine
C. Pyridostigmine
D. Edrophonium (Correct Answer)

Explanation: ***Edrophonium*** - **Edrophonium** is a **short-acting acetylcholinesterase inhibitor** that is not a carbamate. - Its action is very rapid in onset and brief in duration, unlike carbamates which have a longer duration of action due to a more stable bond with acetylcholinesterase. *Physostigmine* - **Physostigmine** is a **tertiary amine carbamate** that can cross the blood-brain barrier. - It works by reversibly inhibiting acetylcholinesterase, leading to increased acetylcholine levels, and has a duration of action of 2-4 hours. *Neostigmine* - **Neostigmine** is a **quaternary ammonium carbamate** that does not cross the blood-brain barrier effectively. - It is used to treat myasthenia gravis and reverse the effects of non-depolarizing neuromuscular blockers, with a duration of action of 2-4 hours. *Pyridostigmine* - **Pyridostigmine** is also a **quaternary ammonium carbamate** and is commonly used for the long-term treatment of myasthenia gravis. - Like neostigmine, it does not cross the blood-brain barrier and has a longer duration of action (3-6 hours) compared to physostigmine.

Question 635: Sympathomimetic drugs are useful in the therapy of all of the following conditions except:

A. Hypotension
B. Acute decompensated heart failure
C. Hypertension (Correct Answer)
D. Nasal congestion

Explanation: ***Hypertension*** - Sympathomimetic drugs **mimic the effects of the sympathetic nervous system**, leading to **increased heart rate, contractility, and vasoconstriction**, which would worsen hypertension. - Their primary action is to activate **adrenergic receptors**, thereby elevating blood pressure rather than lowering it. - Sympathomimetics are **contraindicated in hypertensive patients** as they would exacerbate the elevated blood pressure. *Hypotension* - Sympathomimetic drugs are highly effective in treating hypotension, particularly in conditions like **shock**. - They cause **vasoconstriction (alpha-1 agonism)** and/or **increased cardiac output (beta-1 agonism)**, thereby raising blood pressure. - Agents like **norepinephrine, phenylephrine, and dopamine** are commonly used in critical care settings. *Acute decompensated heart failure* - Sympathomimetics with **beta-1 adrenergic agonist** effects (e.g., **dobutamine**) can improve cardiac contractility and output in acute decompensated heart failure. - These agents help to **increase myocardial performance** in situations where the heart is failing to pump adequately. - They provide temporary hemodynamic support in acute settings. *Nasal congestion* - **Alpha-1 adrenergic agonists** (e.g., **phenylephrine, pseudoephedrine**) are widely used as nasal decongestants. - They cause **vasoconstriction of nasal blood vessels**, reducing mucosal edema and improving airflow. - Available as both topical nasal sprays and oral formulations for symptomatic relief of nasal congestion.

Question 636: The neurotransmitters noradrenaline, adrenaline, and dopamine act through which of the following receptors?

A. Single-pass transmembrane receptor
B. Four-pass transmembrane receptor
C. Seven-pass transmembrane receptor (Correct Answer)
D. Ligand-gated ion channel

Explanation: ***Seven-pass transmembrane receptor*** - Noradrenaline, adrenaline, and dopamine are **catecholamines** that primarily activate **G-protein coupled receptors (GPCRs)**, which are characterized by having seven transmembrane domains. - These receptors mediate a wide range of physiological responses by initiating **intracellular signaling cascades** upon ligand binding. *Single-pass transmembrane receptor* - These receptors, such as **receptor tyrosine kinases**, cross the membrane only once and typically dimerize upon ligand binding to activate their intracellular kinase domains. - While important for growth factors and hormones, they are **not the primary receptors** for catecholamines. *Four-pass transmembrane receptor* - This type of receptor structure is less common for neurotransmitters and is not characteristic of the established receptors for **noradrenaline, adrenaline, and dopamine**. - Examples include some **gap junction proteins** and a subset of ion channels, but not the **adrenergic** or **dopaminergic receptors**. *Ligand-gated ion channel* - These channels directly open in response to ligand binding, allowing ions to pass and rapidly changing the **membrane potential**. - While some neurotransmitters like **acetylcholine (nicotinic receptors)** and **GABA** act this way, catecholamines primarily exert their effects through **GPCRs**, which modulate ion channel activity indirectly.

Question 637: In thyrotoxicosis, which of the following symptoms is least effectively controlled by beta-blockers?

A. Oxygen consumption (Correct Answer)
B. Tremors
C. Tachycardia
D. Anxiety

Explanation: ***Oxygen consumption*** - Beta-blockers primarily address the **adrenergic manifestations** of thyrotoxicosis, but they do not directly inhibit the increased **metabolic rate** or **thyroid hormone production** that drives higher oxygen consumption. - The elevated oxygen consumption in thyrotoxicosis is a direct result of enhanced cellular metabolism due to excess thyroid hormones, which beta-blockers do not counteract. *Tremors* - **Thyrotoxic tremors** are significantly mediated by **beta-adrenergic stimulation**, making them highly responsive to beta-blocker therapy. - Blocking beta-receptors reduces the sympathetic drive that contributes to these fine muscle tremors. *Tachycardia* - **Tachycardia** in thyrotoxicosis is a classic symptom of **increased sympathetic activity**, which beta-blockers effectively block. - Beta-blockers reduce heart rate by inhibiting beta-1 receptors in the myocardium, thereby relieving palpitations and rapid heart rate. *Anxiety* - **Anxiety** is often secondary to the **adrenergic overactivity** and overall heightened metabolic state associated with thyrotoxicosis. - By dampening the sympathetic nervous system, beta-blockers can alleviate anxiety and nervousness.

Question 638: Which of the following drugs possesses the maximum action on nicotinic receptors?

A. Carbachol (Correct Answer)
B. Bethanechol
C. Pilocarpine
D. Methacholine

Explanation: ***Carbachol*** - **Carbachol** is a stable choline ester with prominent **nicotinic agonist activity**, making it the cholinergic agent with the greatest action on nicotinic receptors among the options listed. - Its **dual muscarinic and nicotinic effects** are due to its chemical structure, making it less selective than some other cholinergic agents. *Bethanechol* - **Bethanechol** is a choline ester that primarily acts on **muscarinic receptors** and has very little to no nicotinic activity. - It is used clinically for its muscarinic effects, such as increasing **bladder motility** or treating **gastric atony**. *Pilocarpine* - **Pilocarpine** is an alkaloid with strong, selective **muscarinic agonist activity**, making it particularly useful for conditions like **glaucoma** (by increasing aqueous humor outflow) and **xerostomia**. - It exhibits negligible activity at **nicotinic receptors**. *Methacholine* - **Methacholine** is a choline ester that primarily stimulates **muscarinic receptors**, though it has more nicotinic action than bethanechol. - It is known for its use in **bronchial challenge tests** to diagnose **asthma** due to its role in causing bronchoconstriction via muscarinic stimulation.

Question 639: What distinguishes betaxolol from timolol in terms of its pharmacological properties?

A. Is a selective β1 blocker (Correct Answer)
B. Has superior efficacy in treating glaucoma
C. Causes fewer ocular side effects than timolol
D. Has a shorter duration of action than timolol

Explanation: ***Is a selective β1 blocker*** - **Betaxolol** is a **cardioselective β1-adrenergic antagonist**, meaning it primarily blocks β1 receptors in the heart and **juxtaglomerular apparatus**. - **Timolol**, in contrast, is a **non-selective β-blocker**, affecting both β1 and β2 receptors, which can lead to more systemic side effects. *Has superior efficacy in treating glaucoma* - Both betaxolol and timolol are effective in **reducing intraocular pressure (IOP)** by decreasing aqueous humor production, with **timolol generally showing equivalent or slightly greater efficacy**. - **Timolol's non-selective action** may sometimes lead to a marginal advantage in IOP reduction, though **betaxolol is preferred** in some patients due to its selectivity. *Causes fewer ocular side effects than timolol* - While betaxolol is generally associated with **fewer systemic side effects** due to its cardioselectivity, it can actually cause **more ocular stinging and irritation** compared to timolol. - Some studies suggest a comparable incidence of other ocular side effects like **dry eye or blurred vision** between the two drugs. *Has a shorter duration of action than timolol* - Both betaxolol and timolol are applied **topically once or twice daily** to manage glaucoma, indicating a **similar long duration of action** suitable for sustained IOP control. - There is no clinical evidence to suggest that betaxolol has a significantly shorter duration of action that would warrant more frequent dosing compared to timolol.

Question 640: Which of the following statements about d-tubocurarine is true?

A. Is a non-depolarizing neuromuscular blocking agent. (Correct Answer)
B. Causes histamine release leading to hypotension.
C. Blocks nicotinic receptors at the neuromuscular junction.
D. Has intermediate duration of action (30-60 minutes).

Explanation: ***Is a non-depolarizing neuromuscular blocking agent*** - D-tubocurarine is a **classic non-depolarizing neuromuscular blocker (NDNMB)**, acting as a competitive antagonist at nicotinic receptors - This is the **fundamental classification** that defines its mechanism and distinguishes it from depolarizing agents like succinylcholine - Non-depolarizing agents can be reversed with anticholinesterases (neostigmine, pyridostigmine) *Causes histamine release leading to hypotension* - While this statement is **medically accurate**, d-tubocurarine does cause significant histamine release - This side effect leads to hypotension, bronchospasm, and tachycardia - However, this is a **side effect** rather than the primary defining characteristic of the drug *Blocks nicotinic receptors at the neuromuscular junction* - This statement is also **factually correct** - d-tubocurarine blocks nicotinic ACh receptors at NMJ - This is the **mechanism of action** of all non-depolarizing blockers - However, the classification as "non-depolarizing" is the broader, more fundamental concept tested *Has intermediate duration of action (30-60 minutes)* - This is **INCORRECT** - d-tubocurarine is classified as a **long-acting** neuromuscular blocker - Duration of action: **90-120+ minutes**, not intermediate - Intermediate-acting agents include atracurium, vecuronium, and rocuronium (30-60 min)

Practice by Chapter

Cholinergic Agonists

Practice Questions

Cholinergic Antagonists

Practice Questions

Adrenergic Agonists

Practice Questions

Adrenergic Antagonists

Practice Questions

Ganglionic Agents

Practice Questions

Neuromuscular Blocking Agents

Practice Questions

Autonomic Drugs in Ophthalmology

Practice Questions

Autonomic Drugs in Cardiovascular Disease

Practice Questions

Autonomic Drugs in Respiratory Disease

Practice Questions

Autonomic Drugs in Urological Disorders

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free