Autonomic Nervous System Drugs Practice Questions

Q: Choline esters like carbachol are most likely to cause which of the following adverse effects?

Salivation. **Explanation:** Carbachol is a **direct-acting cholinergic agonist** (choline ester) that stimulates both muscarinic (M) and nicotinic (N) receptors. The adverse effect profile of such drugs is a direct extension of their parasympathomimetic actions, often summarized by the mnemonic **DUMBELS** (Diarrhea, Urination, Miosis, Bradycardia/Bronchospasm, Emesis, Lacrimation, Salivation). **Why Salivation is Correct:** Cholinergic drugs stimulate **M3 receptors** located on exocrine glands. Activation of these receptors on salivary glands leads to increased secretions (sialorrhea). This is a classic "SLUDGE" (Salivation, Lacrimation, Urination, Defecation, GI distress, Emesis) sign of cholinergic excess. **Analysis of Incorrect Options:** * **A. Delirium:** This is a feature of **Atropine poisoning** (anticholinergic toxicity), often described as "Mad as a hatter." Choline esters like carbachol are quaternary ammonium compounds; they are highly polar and do not easily cross the blood-brain barrier to cause CNS effects like delirium. * **B. Anhydrosis:** Cholinergic drugs cause **diaphoresis** (excessive sweating) via M3 receptors on eccrine sweat glands. Anhydrosis (dry skin) is a side effect of anticholinergics (e.g., Atropine). * **C. Tachycardia:** Parasympathetic stimulation typically causes **bradycardia** (via M2 receptors in the SA node). Tachycardia is a sympathetic response or a result of muscarinic blockade. **High-Yield Clinical Pearls for NEET-PG:** * **Carbachol vs. Bethanechol:** Carbachol has both Muscarinic and Nicotinic activity, whereas Bethanechol is purely Muscarinic. * **Resistance:** Unlike Acetylcholine, Carbachol is resistant to hydrolysis by both acetylcholinesterase and pseudocholinesterase, leading to a prolonged duration of action. * **Clinical Use:** Carbachol is primarily used topically in the eye to produce miosis and reduce intraocular pressure in glaucoma.

Q: What is the effect of cocaine on blood vessels?

Vasoconstrictor. ### Explanation **1. Why Option A is Correct:** Cocaine acts as an indirect-acting sympathomimetic. Its primary mechanism is the **inhibition of the Reuptake-1 transporter (NET)** at the presynaptic nerve terminal. This prevents the reabsorption of norepinephrine (NE) from the synaptic cleft, leading to a significant increase in NE concentration. This excess NE stimulates **$\alpha_1$-adrenergic receptors** on the vascular smooth muscle, resulting in potent **vasoconstriction**. **2. Why Other Options are Incorrect:** * **Option B (Vasodilator):** Cocaine does not stimulate $\beta_2$ receptors or release nitric oxide to a degree that would cause vasodilation. Its dominant effect is $\alpha$-mediated constriction. * **Option C (Vasoineffective):** Cocaine has profound cardiovascular effects, including hypertension and tachycardia; it is never hemodynamically neutral. * **Option D (First constricts then dilates):** This describes a "biphasic response" (like low-dose epinephrine). Cocaine’s effect is consistently vasoconstrictive due to the sustained presence of NE in the synapse. **3. High-Yield Clinical Pearls for NEET-PG:** * **Local Anesthetic Exception:** Cocaine is the **only** local anesthetic that is a vasoconstrictor. All other local anesthetics (e.g., Lidocaine) are vasodilators. * **Clinical Use:** Due to its vasoconstrictive and anesthetic properties, it is used topically in ENT surgeries (e.g., rhinoplasty) to reduce bleeding. * **Contraindication:** Never use **$\beta$-blockers** (like Propranolol) in cocaine toxicity. Blocking $\beta_2$ (vasodilation) leaves $\alpha_1$ stimulation unopposed, leading to a hypertensive crisis and coronary vasospasm (Prinzmetal angina). * **Organ Damage:** Chronic use causes midline destructive lesions (septal perforation) due to ischemic necrosis from prolonged vasoconstriction.

Q: Dale's vasomotor reversal phenomenon occurs with which of the following?

Adrenaline. **Explanation:** **Dale’s Vasomotor Reversal** (also known as the Dale’s Phenomenon) refers to the paradoxical fall in blood pressure when Adrenaline is administered after an alpha-blocker (like Phentolamine or Ergotoxine). **1. Why Adrenaline is correct:** Adrenaline acts on both **α-receptors** (vasoconstriction) and **β2-receptors** (vasodilation). Under normal conditions, the α-response predominates, leading to a rise in blood pressure. However, if an α-blocker is given first, the α-receptors are occupied. When Adrenaline is subsequently administered, it can only act on the "unmasked" β2-receptors in the skeletal muscle blood vessels, leading to profound vasodilation and a **fall in blood pressure** (reversal of the usual pressor effect). **2. Why other options are incorrect:** * **Noradrenaline:** It acts primarily on α1, α2, and β1 receptors with **negligible action on β2 receptors**. Therefore, even after α-blockade, there is no significant β2-mediated vasodilation to cause a fall in BP. * **Dopamine:** While Dopamine has complex dose-dependent effects, it does not typically exhibit the classic "vasomotor reversal" described by Dale, which specifically characterizes the dual α and β2 nature of Adrenaline. **High-Yield Clinical Pearls for NEET-PG:** * **The "Rule of Adrenaline":** Small dose = β effect (Vasodilation); Large dose = α effect (Vasoconstriction). * **Vasomotor Reversal of Sir Henry Dale** is the classic pharmacological demonstration of the dual nature of Adrenaline. * **Clinical Application:** In patients with Pheochromocytoma, always give an **α-blocker before a β-blocker** to prevent a hypertensive crisis caused by unopposed α-stimulation.

Q: Intravenous administration of norepinephrine in a patient already taking an effective dose of atropine will often:

Increase heart rate. **Explanation:** The correct answer is **A. Increase heart rate.** **Mechanism:** Norepinephrine (NE) is a potent agonist at $\alpha_1$, $\alpha_2$, and $\beta_1$ receptors. When administered alone, NE causes intense vasoconstriction ($\alpha_1$), leading to a significant rise in mean arterial pressure. This triggers a **compensatory baroreceptor reflex**, which increases vagal (parasympathetic) tone to the heart, resulting in **reflex bradycardia**. However, **Atropine** is a muscarinic antagonist that blocks the effects of the vagus nerve on the heart. By "pre-treating" with atropine, the baroreceptor-mediated reflex bradycardia is abolished. Consequently, the direct stimulatory effect of NE on cardiac **$\beta_1$ receptors** is unmasked, leading to an increase in heart rate (tachycardia). **Analysis of Incorrect Options:** * **B. Decrease total peripheral resistance:** Incorrect. NE causes profound vasoconstriction via $\alpha_1$ receptors, which significantly *increases* total peripheral resistance. * **C. Decrease pupil size:** Incorrect. NE acts on $\alpha_1$ receptors in the radial muscle of the iris to cause mydriasis (dilation), not miosis (contraction). * **D. Have no effect:** Incorrect. NE is a potent sympathomimetic with significant hemodynamic effects. **NEET-PG High-Yield Pearls:** * **Vagal Escape:** Atropine "unmasks" the direct $\beta_1$ effect of drugs that otherwise cause reflex bradycardia (like NE or Phenylephrine). * **Norepinephrine vs. Epinephrine:** NE lacks significant $\beta_2$ activity; therefore, it does not cause vasodilation or a drop in diastolic blood pressure, unlike Epinephrine. * **Drug of Choice:** NE is the first-line vasopressor for **septic shock**.

Q: The unknown drug is likely to be:

High dose adrenaline. ***High dose adrenaline*** - At high doses, adrenaline activates **α1 receptors** causing **vasoconstriction** and increased **peripheral resistance**, leading to elevated **DBP** in addition to increased **SBP**. - **β1 receptor** activation increases **heart rate** and **cardiac contractility**, while **α1 dominance** at high doses overcomes **β2-mediated vasodilation**. *Low dose adrenaline* - At low doses, **β2 receptor** activation predominates, causing **vasodilation** in skeletal muscle vessels and **decreased DBP**. - Would show increased **SBP** and **heart rate** but **decreased or unchanged DBP** due to **β2-mediated peripheral vasodilation**. *Nor-adrenaline* - Primarily activates **α1 and β1 receptors** with minimal **β2 activity**, causing **vasoconstriction** and increased **peripheral resistance**. - Typically causes **reflex bradycardia** due to **baroreceptor activation** from increased **blood pressure**, not increased heart rate. *Isoprenaline* - Pure **β-agonist** (β1 and β2) with no **α-receptor** activity, causing **vasodilation** and **decreased peripheral resistance**. - Would increase **heart rate** and **SBP** but significantly **decrease DBP** due to **β2-mediated vasodilation**.

Q: Phase II block is seen in which of the following agents?

Suxamethonium. **Suxamethonium (Succinylcholine)** is a depolarizing neuromuscular blocker (D-NMB) [2]. It produces two distinct types of neuromuscular blockade [1]:* **Phase I Block (Depolarizing):** The initial phase where the drug acts as an agonist at nicotinic receptors, causing persistent depolarization and transient fasciculations [1, 3].* **Phase II Block (Desensitizing):** Occurs with **prolonged exposure** or high doses. The membrane repolarizes, but the receptors become desensitized and unresponsive to Acetylcholine. This phase resembles a non-depolarizing block (competitive) and can be partially reversed by anticholinesterases [1, 3].**Analysis of Incorrect Options:** * **A & B (Halothane and Ether):** These are volatile inhalational anesthetics. While they can potentiate the effects of neuromuscular blockers by relaxing skeletal muscle, they do not cause a Phase II block themselves. * **C (D-tubocurarine):** This is a classic non-depolarizing (competitive) neuromuscular blocker. It produces a competitive block from the onset (characterized by "fade" on Train-of-Four monitoring) and does not transition through phases.**High-Yield Clinical Pearls for NEET-PG:** * **Pseudocholinesterase Deficiency:** Suxamethonium is metabolized by plasma pseudocholinesterase. Patients with a genetic deficiency of this enzyme experience **prolonged apnea** after a standard dose. * **Side Effects:** Hyperkalemia (dangerous in burn/trauma patients), malignant hyperthermia (treated with **Dantrolene**), and postoperative myalgia. * **Monitoring:** Phase II block is identified using a nerve stimulator; it shows a "fade" in the Train-of-Four (TOF) response, similar to non-depolarizing agents.

Q: Carvedilol is an effective antihypertensive agent that, like propranolol, is capable of blocking beta receptors. An important difference between the two drugs is that carvedilol

has a1 receptor blocking actions. ### Explanation **Core Concept:** Carvedilol belongs to a unique class of **third-generation non-selective beta-blockers**. Unlike Propranolol (a first-generation non-selective beta-blocker), Carvedilol possesses additional **$\alpha_1$-receptor blocking activity**. This dual action results in peripheral vasodilation (via $\alpha_1$ blockade) alongside decreased heart rate and contractility (via $\beta$ blockade), making it highly effective in treating hypertension and chronic heart failure. **Analysis of Options:** * **Option D (Correct):** Carvedilol provides a "balanced" hemodynamic effect. While $\beta$-blockade prevents reflex tachycardia, the $\alpha_1$-blockade reduces peripheral vascular resistance. * **Option A (Incorrect):** Carvedilol is primarily administered **orally**. It is not used as eye drops; Timolol and Betaxolol are the standard beta-blockers used topically for glaucoma. * **Option B (Incorrect):** Carvedilol does **not** have Intrinsic Sympathomimetic Activity (ISA). Drugs with ISA (like Pindolol or Acebutolol) act as partial agonists. * **Option C (Incorrect):** Carvedilol is **non-selective**, blocking $\beta_1$, $\beta_2$, and $\alpha_1$ receptors. Selective $\beta_1$ blockers (cardioselective) include Metoprolol, Atenolol, and Bisoprolol. **High-Yield NEET-PG Pearls:** 1. **Antioxidant Properties:** Carvedilol has unique antioxidant and anti-proliferative properties, which contribute to its mortality benefit in **Congestive Heart Failure (CHF)**. 2. **Labetalol vs. Carvedilol:** Both block $\alpha$ and $\beta$ receptors. However, Labetalol is the drug of choice for **hypertensive emergencies in pregnancy**, while Carvedilol is a cornerstone for **chronic heart failure** management. 3. **Membrane Stabilizing Activity:** Like Propranolol, Carvedilol possesses local anesthetic (membrane stabilizing) activity. 4. **Metabolism:** It is highly lipophilic and undergoes extensive hepatic metabolism.

Q: All the following drugs are used in the management of pheochromocytoma except?

Atenolol. **Explanation:** The management of **Pheochromocytoma** requires a specific sequence of pharmacological blockade to prevent a hypertensive crisis. **Why Atenolol is the correct answer:** Atenolol is a selective **$\beta_1$-blocker**. In pheochromocytoma, the tumor secretes massive amounts of catecholamines. If a $\beta$-blocker is administered alone (or before $\alpha$-blockade), it blocks $\beta_2$-mediated vasodilation in skeletal muscle. This leaves the $\alpha$-receptors unopposed, leading to exaggerated vasoconstriction and a life-threatening rise in blood pressure (**"unopposed alpha stimulation"**). Therefore, $\beta$-blockers are contraindicated as monotherapy. **Analysis of incorrect options:** * **Prazosin:** A selective $\alpha_1$-blocker used to control hypertension. In clinical practice, **Phenoxybenzamine** (non-selective, irreversible $\alpha$-blocker) is the traditional drug of choice for preoperative preparation. * **Nitroprusside:** A potent vasodilator used intravenously to manage **hypertensive crises** during surgical resection of the tumor. * **Metyrosine:** An inhibitor of the enzyme **tyrosine hydroxylase** (the rate-limiting step in catecholamine synthesis). It is used in inoperable or metastatic cases to reduce the total catecholamine pool. **NEET-PG High-Yield Pearls:** 1. **Golden Rule:** Always give **Alpha blockers BEFORE Beta blockers** (usually 7–14 days prior to surgery). 2. **Drug of Choice (Pre-op):** Phenoxybenzamine. 3. **Intra-operative HTN:** Sodium Nitroprusside or Phentolamine. 4. **Intra-operative Arrhythmia:** Lidocaine or Esmolol (only after $\alpha$-blockade). 5. **Metyrosine Mechanism:** Inhibits Tyrosine $\rightarrow$ DOPA conversion.

Q: Which of the following is a long-acting non-depolarizing muscle relaxant?

Pancuronium. ### Explanation **Pancuronium** is the correct answer because it is a classic **long-acting** steroid-based non-depolarizing neuromuscular blocking agent (NMBA). It typically has a duration of action exceeding 60–90 minutes. It works by competitively antagonizing nicotinic acetylcholine receptors at the neuromuscular junction. **Analysis of Options:** * **Succinylcholine (Option A):** This is a **depolarizing** muscle relaxant. It is known for its rapid onset (30–60 seconds) and ultra-short duration (5–10 minutes), making it the drug of choice for rapid sequence induction (RSI). * **Mivacurium (Option B):** This is a non-depolarizing NMBA, but it is categorized as **short-acting** (duration ~15–20 minutes). It is unique because it is metabolized by plasma cholinesterase. * **Phenylephrine (Option D):** This is not a muscle relaxant; it is a selective **alpha-1 adrenergic agonist** used as a vasopressor to treat hypotension. **High-Yield NEET-PG Pearls:** 1. **Vagolytic Effect:** Pancuronium is notorious for causing **tachycardia** because it inhibits muscarinic receptors in the SA node. This makes it useful in pediatric cardiac surgery but risky in patients with CAD. 2. **Metabolism:** Pancuronium is primarily excreted by the **kidneys** (up to 80%); therefore, its duration is significantly prolonged in patients with renal failure. 3. **Classification by Duration:** * **Short-acting:** Mivacurium. * **Intermediate-acting:** Vecuronium, Atracurium, Cisatracurium, Rocuronium. * **Long-acting:** Pancuronium, Pipecuronium, Doxacurium. 4. **Hoffmann Elimination:** Remember that **Atracurium and Cisatracurium** undergo spontaneous degradation (Hoffmann elimination), making them the drugs of choice in liver and kidney failure.

Question 1

Choline esters like carbachol are most likely to cause which of the following adverse effects?

Accepted Answer

Salivation

Answer

Delirium

Answer

Anhydrosis (dry skin)

Answer

Tachycardia

Question 2

What is the effect of cocaine on blood vessels?

Accepted Answer

Vasoconstrictor

Answer

Vasodilator

Answer

Vasoineffective

Answer

First constricts then dilates

Question 3

Dale's vasomotor reversal phenomenon occurs with which of the following?

Accepted Answer

Adrenaline

Answer

Dopamine

Answer

Noradrenaline

Answer

All of the above

Question 4

A 32-year-old woman had abdominal surgery, after which she complains about difficulty in urination. Cholinomimetic stimulation with bethanechol or neostigmine is beneficial in relieving post-operative urinary retention. Neostigmine and bethanechol in moderate doses are likely to have different effects on what?

Accepted Answer

Vascular endothelium

Answer

Salivary glands

Answer

Ureteral tone

Answer

Gastric secretory cells

Question 5

Intravenous administration of norepinephrine in a patient already taking an effective dose of atropine will often:

Accepted Answer

Increase heart rate

Answer

Decrease total peripheral resistance

Answer

Decrease pupil size

Answer

Have no effect on the cardiovascular system

Question 6

The unknown drug is likely to be:

Accepted Answer

High dose adrenaline

Answer

Low dose adrenaline

Answer

Nor-adrenaline

Answer

Isoprenaline

Question 7

Phase II block is seen in which of the following agents?

Accepted Answer

Suxamethonium

Answer

Halothane

Answer

Ether

Answer

D-tubocurarine

Question 8

Carvedilol is an effective antihypertensive agent that, like propranolol, is capable of blocking beta receptors. An important difference between the two drugs is that carvedilol

Accepted Answer

has a1 receptor blocking actions

Answer

is available only as eye drops

Answer

has intrinsic sympathomimetic activity

Answer

is a selective blocker of cardiac b1 receptors

Question 9

All the following drugs are used in the management of pheochromocytoma except?

Accepted Answer

Atenolol

Answer

Prazosin

Answer

Nitroprusside

Answer

Metyrosine

Question 10

Which of the following is a long-acting non-depolarizing muscle relaxant?

Accepted Answer

Pancuronium

Answer

Succinylcholine

Answer

Mivacurium

Answer

Phenylephrine

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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