Autonomic Nervous System Drugs — MCQs
On this page
Which of the following is a selective alpha-2 agonist?
A physician used edrophonium to differentiate between a myasthenic crisis and a cholinergic crisis. What property makes it preferred over other anticholinesterase agents for this purpose?
Physostigmine was therapeutically used for the first time in the treatment of glaucoma in 1877 by whom?
Which anticholinergic agent is commonly used to reverse the action of neuromuscular blockers?
Which receptor does dobutamine primarily act upon?
Which of the following is a selective beta-2 blocker?
All of the following drugs are useful in detrusor instability EXCEPT?
Effects of d-tubocurarine are reversed by?
Vecuronium acts on which of the following structures?
Which drug is not used in the management of glaucoma?
Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs
Question 181: Which of the following is a selective alpha-2 agonist?
- A. Tizanidine (Correct Answer)
- B. Prazosin
- C. Adrenaline
- D. Propranolol
Explanation: **Explanation:** **Correct Option: A. Tizanidine** Tizanidine is a **selective alpha-2 ($\alpha_2$) adrenergic agonist**. It acts primarily in the central nervous system (spinal cord and supraspinal levels) to increase presynaptic inhibition of motor neurons. By reducing the release of excitatory amino acids, it effectively reduces muscle spasticity. It is clinically used to manage spasticity associated with conditions like multiple sclerosis or spinal cord injury. **Analysis of Incorrect Options:** * **B. Prazosin:** This is a selective **alpha-1 ($\alpha_1$) blocker**. It is primarily used in the treatment of hypertension and Benign Prostatic Hyperplasia (BPH) because it causes vasodilation and relaxes prostatic smooth muscle. * **C. Adrenaline:** This is a **non-selective adrenergic agonist**. It acts on $\alpha_1, \alpha_2, \beta_1,$ and $\beta_2$ receptors. It is the drug of choice for anaphylactic shock. * **D. Propranolol:** This is a **non-selective beta-blocker** ($\beta_1$ and $\beta_2$). It is used for hypertension, prophylaxis of migraine, and performance anxiety, but has no agonist activity at alpha receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Other Alpha-2 Agonists:** Clonidine (antihypertensive), Methyldopa (drug of choice for hypertension in pregnancy), Dexmedetomidine (sedative used in ICUs), and Brimonidine/Apraclonidine (used in glaucoma). * **Mechanism:** $\alpha_2$ receptors are G-protein coupled receptors ($G_i$) that inhibit adenylyl cyclase, leading to decreased cAMP and decreased neurotransmitter release. * **Side Effects of Tizanidine:** Hypotension (due to its structural similarity to clonidine), sedation, and xerostomia (dry mouth).
Question 182: A physician used edrophonium to differentiate between a myasthenic crisis and a cholinergic crisis. What property makes it preferred over other anticholinesterase agents for this purpose?
- A. Shorter duration of action (Correct Answer)
- B. Longer duration of action
- C. Direct action on the muscle end plate
- D. Selective inhibition of true cholinesterase
Explanation: **Explanation:** The differentiation between a **myasthenic crisis** (under-dosage of anticholinesterases) and a **cholinergic crisis** (over-dosage) is critical because their treatments are diametrically opposed. This is clinically achieved using the **Tensilon Test** (Edrophonium test). **Why Option A is Correct:** Edrophonium is a quaternary ammonium compound that binds reversibly to the anionic site of acetylcholinesterase via ionic bonds. It has an **extremely rapid onset (30–60 seconds)** and a **very short duration of action (5–10 minutes)**. * If the patient has a **myasthenic crisis**, their muscle strength will briefly improve. * If the patient has a **cholinergic crisis**, their muscle weakness will briefly worsen. The short duration ensures that if the patient’s condition worsens (cholinergic crisis), the life-threatening respiratory depression or bradycardia will be transient and subside quickly. **Why Other Options are Incorrect:** * **Option B:** A longer duration of action (like Neostigmine or Pyridostigmine) would be dangerous; if the patient were in a cholinergic crisis, the prolonged worsening of symptoms could lead to fatal respiratory failure. * **Option C:** While some agents like Neostigmine have a minor direct agonist effect on nicotinic receptors, this is not the primary reason for choosing Edrophonium for diagnosis. * **Option D:** Edrophonium is a non-selective inhibitor of acetylcholinesterase; selectivity for "true" vs. "pseudo" cholinesterase is not the clinical basis for this test. **High-Yield NEET-PG Pearls:** * **Antidote:** Atropine should always be kept ready during a Tensilon test to manage potential bradycardia or excessive salivation. * **Other uses of Edrophonium:** Diagnosis of Myasthenia Gravis and assessment of the adequacy of oral anticholinesterase therapy. * **Treatment of MG:** Pyridostigmine is the drug of choice for long-term maintenance due to its longer duration of action.
Question 183: Physostigmine was therapeutically used for the first time in the treatment of glaucoma in 1877 by whom?
- A. Laqueur (Correct Answer)
- B. Posselt and Reiman
- C. Ahlquist
- D. Sir James Black
Explanation: **Explanation:** The correct answer is **Laqueur (Option A)**. In 1877, Ludwig Laqueur, a German ophthalmologist, was the first to therapeutically apply physostigmine (eserine) for the treatment of glaucoma. Physostigmine is a reversible anticholinesterase that increases acetylcholine levels at the iris sphincter and ciliary muscle, leading to miosis and contraction of the ciliary muscle. This action facilitates the drainage of aqueous humor through the canal of Schlemm, thereby reducing intraocular pressure. **Analysis of Incorrect Options:** * **Posselt and Reiman (B):** They are credited with the first isolation of nicotine from tobacco leaves in 1828. * **Ahlquist (C):** Raymond Ahlquist is famous for his 1948 landmark paper that classified adrenoceptors into alpha ($\alpha$) and beta ($\beta$) subtypes based on their responses to various catecholamines. * **Sir James Black (D):** He was a Nobel laureate who developed the first clinically significant beta-blocker (Propranolol) and the first $H_2$ receptor antagonist (Cimetidine). **High-Yield Clinical Pearls for NEET-PG:** * **Physostigmine:** It is a tertiary amine, meaning it is lipid-soluble and **crosses the blood-brain barrier (BBB)**. This makes it the drug of choice for treating **Atropine (anticholinergic) poisoning**. * **Glaucoma Management:** While physostigmine was historically significant, modern management typically utilizes prostaglandin analogs (Latanoprost), beta-blockers (Timolol), or alpha-2 agonists (Brimonidine). * **Source:** Physostigmine is naturally derived from the **Calabar bean** (*Physostigma venenosum*).
Question 184: Which anticholinergic agent is commonly used to reverse the action of neuromuscular blockers?
- A. Edrophonium
- B. Physostigmine
- C. Pyridostigmine
- D. Neostigmine (Correct Answer)
Explanation: ### Explanation **Correct Answer: D. Neostigmine** **Mechanism of Action:** To reverse the effects of non-depolarizing neuromuscular blockers (like Vecuronium or Rocuronium), we must increase the concentration of Acetylcholine (ACh) at the neuromuscular junction (NMJ) to outcompete the blocker. **Neostigmine** is a quaternary ammonium **reversible acetylcholinesterase inhibitor**. By inhibiting the enzyme that breaks down ACh, it increases ACh levels at the nicotinic receptors of the NMJ, thereby restoring muscle contraction. **Analysis of Options:** * **A. Edrophonium:** It is a very short-acting cholinesterase inhibitor. While it can be used for reversal, its duration is often shorter than the muscle relaxant itself, leading to "recurarization" (re-paralysis). It is primarily used for the **Tensilon test** in Myasthenia Gravis. * **B. Physostigmine:** This is a tertiary amine that **crosses the blood-brain barrier (BBB)**. Because it enters the CNS, it is not preferred for peripheral NMJ reversal; its primary clinical use is as an antidote for **Atropine poisoning**. * **C. Pyridostigmine:** While it is a quaternary ammonium compound similar to Neostigmine, it has a slower onset and longer duration. It is the **drug of choice for the oral maintenance treatment of Myasthenia Gravis**, rather than acute anesthetic reversal. **High-Yield Clinical Pearls for NEET-PG:** * **Co-administration:** Neostigmine increases ACh at both nicotinic and muscarinic sites. To prevent unwanted muscarinic side effects (bradycardia, salivation), it is always administered with an antimuscarinic agent like **Glycopyrrolate** (preferred due to similar onset) or **Atropine**. * **Ceiling Effect:** Cholinesterase inhibitors have a "ceiling effect"; they cannot reverse a profound "dense" block. * **Sugammadex:** A newer agent that reverses Rocuronium/Vecuronium by direct encapsulation (chelation), bypassing the ACh system entirely.
Question 185: Which receptor does dobutamine primarily act upon?
- A. Beta 1 (Correct Answer)
- B. Beta 2
- C. Alpha 1
- D. Alpha 2
Explanation: **Explanation:** Dobutamine is a synthetic catecholamine and a relatively selective **$\beta_1$-adrenergic agonist**. Its primary mechanism of action involves the stimulation of $\beta_1$ receptors in the myocardium, which increases intracellular cAMP levels. This leads to a potent **positive inotropic effect** (increased contractility) with a comparatively lesser effect on heart rate (chronotropy) and peripheral vascular resistance. **Analysis of Options:** * **Option A (Correct):** Dobutamine’s affinity for $\beta_1$ receptors is significantly higher than its affinity for other adrenergic receptors. This makes it the drug of choice for cardiogenic shock and acute heart failure. * **Option B ($\beta_2$):** While dobutamine has minor $\beta_2$ agonist activity (leading to mild vasodilation), this is not its primary site of action. * **Option C ($\alpha_1$):** Dobutamine exists as a racemic mixture; the (-) isomer is an $\alpha_1$ agonist, but the (+) isomer is an $\alpha_1$ antagonist. These effects largely cancel each other out, resulting in minimal net change in peripheral vascular resistance. * **Option D ($\alpha_2$):** Dobutamine has negligible activity at $\alpha_2$ receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Dobutamine is the preferred inotrope in **Cardiogenic Shock** because it increases cardiac output without significantly increasing myocardial oxygen demand compared to other pressors. * **Dobutamine Stress Echocardiography (DSE):** Used to diagnose ischemic heart disease in patients unable to perform exercise stress tests. * **Side Effect:** Can cause tachyarrhythmias (due to increased AV conduction). * **Comparison:** Unlike Dopamine, Dobutamine does not act on Dopaminergic ($D_1$) receptors and does not cause renal vasodilation.
Question 186: Which of the following is a selective beta-2 blocker?
- A. Butoxamine (Correct Answer)
- B. Betaxolol
- C. Esmolol
- D. Bisoprolol
Explanation: **Explanation:** **Correct Answer: A. Butoxamine** **1. Why Butoxamine is correct:** Butoxamine is a **selective Beta-2 (β2) receptor antagonist**. Unlike most clinically used beta-blockers which target β1 receptors to treat cardiovascular conditions, Butoxamine specifically blocks β2 receptors. In medical research, it is primarily used as a pharmacological tool to identify the presence and function of β2 receptors in various tissues. It has no significant clinical application because blocking β2 receptors can lead to harmful bronchoconstriction and inhibition of glycogenolysis. **2. Why the other options are incorrect:** * **B. Betaxolol:** This is a **selective Beta-1 (β1) blocker** (cardioselective). It is commonly used in the treatment of glaucoma (topical) and hypertension. * **C. Esmolol:** This is an **ultra-short-acting selective Beta-1 (β1) blocker**. It is administered intravenously and is the drug of choice for emergency situations like aortic dissection or supraventricular tachycardia due to its rapid onset and very short half-life (approx. 9 minutes). * **D. Bisoprolol:** This is a highly **selective Beta-1 (β1) blocker**. It is a mainstay in the long-term management of chronic heart failure and hypertension. **3. High-Yield NEET-PG Pearls:** * **Mnemonic for Cardioselective (β1) Blockers:** *"New Beta Blockers Are Exclusive To Man's Alive Heart"* (Nebivolol, Betaxolol, Bisoprolol, Atenolol, Esmolol, Talinolol, Metoprolol, Acebutolol). * **Butoxamine** is the "odd one out" as it is the only specific β2 blocker usually tested. * **Clinical Caution:** Non-selective beta-blockers (like Propranolol) are contraindicated in asthmatics because they block β2 receptors, leading to life-threatening bronchospasm. Butoxamine would theoretically carry the same risk.
Question 187: All of the following drugs are useful in detrusor instability EXCEPT?
- A. Solefenacin
- B. Tolterodine
- C. Flavoxate
- D. Duloxetine (Correct Answer)
Explanation: **Explanation:** **Detrusor instability** (Overactive Bladder) is characterized by involuntary contractions of the detrusor muscle during the filling phase. Since the detrusor is primarily under parasympathetic control via **M3 muscarinic receptors**, the mainstay of treatment is **Antimuscarinics**. **Why Duloxetine is the Correct Answer:** **Duloxetine** is a Serotonin-Norepinephrine Reuptake Inhibitor (SNRI). It is used in the management of **Stress Urinary Incontinence (SUI)**, not detrusor instability. It works by increasing the tone of the external urethral sphincter (striated muscle) via stimulation of Onuf’s nucleus in the sacral spinal cord. It does not relax the detrusor muscle. **Analysis of Other Options:** * **Solifenacin & Tolterodine:** These are competitive **M3-selective antagonists**. They are the first-line pharmacological treatments for overactive bladder as they decrease detrusor pressure and increase bladder capacity. * **Flavoxate:** This is a tertiary amine with direct **antispasmodic** action on the smooth muscle of the bladder. It also possesses weak anticholinergic and local anesthetic properties, making it useful for symptomatic relief of bladder spasms. **NEET-PG High-Yield Pearls:** * **Mirabegron:** A **$\beta_3$-agonist** used for detrusor instability; it relaxes the detrusor by mimicking sympathetic activity. * **Oxybutynin:** Often considered the "gold standard" antimuscarinic but has high side effects (dry mouth, constipation) due to lack of M3 selectivity. * **Drug of choice for Nocturnal Enuresis:** Desmopressin (DOC); Imipramine (alternative). * **Drug of choice for BPH with OAB:** $\alpha_1$-blocker + Antimuscarinic (e.g., Tamsulosin + Solifenacin).
Question 188: Effects of d-tubocurarine are reversed by?
- A. Atropine
- B. Neostigmine (Correct Answer)
- C. Succinylcholine
- D. Barbiturates
Explanation: **Explanation:** **Mechanism of Action (Why Neostigmine is correct):** d-Tubocurarine is a **competitive (non-depolarizing) neuromuscular blocking agent**. It works by competing with Acetylcholine (ACh) for nicotinic receptors ($N_m$) at the motor endplate. To reverse its effects, we must increase the concentration of ACh at the synaptic cleft. **Neostigmine** is an Acetylcholinesterase (AChE) inhibitor; it prevents the breakdown of ACh, allowing the neurotransmitter to accumulate and "out-compete" the d-tubocurarine molecules, thereby restoring muscle contraction. **Analysis of Incorrect Options:** * **Atropine:** This is a muscarinic antagonist. While it does not reverse neuromuscular blockade, it is often co-administered with Neostigmine to prevent the unwanted parasympathetic side effects (bradycardia, salivation) caused by excess ACh at muscarinic sites. * **Succinylcholine:** This is a depolarizing neuromuscular blocker. Adding it to a non-depolarizing block can lead to a complex, unpredictable phase II block and does not serve as a reversal agent. * **Barbiturates:** These are CNS depressants used for induction of anesthesia. They have no specific action at the nicotinic receptor and may actually prolong respiratory depression. **NEET-PG High-Yield Pearls:** * **Sugammadex:** A newer, specific reversal agent for Aminosteroid NMBs (Rocuronium > Vecuronium) that works by chelation (encapsulation), not AChE inhibition. * **Edrophonium:** A rapid-acting AChE inhibitor used in the **Tensilon Test** for Myasthenia Gravis, but less commonly used for NMB reversal due to its short duration. * **Hoffman Elimination:** Remember that **Atracurium** and **Cisatracurium** do not require pharmacological reversal for metabolism as they undergo spontaneous degradation in the plasma.
Question 189: Vecuronium acts on which of the following structures?
- A. Cerebral cortex
- B. Myoneural junction (Correct Answer)
- C. Muscle fibres
- D. Spinal cord
Explanation: **Explanation:** **Vecuronium** is a non-depolarizing neuromuscular blocking agent (NMBA) belonging to the aminosteroid group. 1. **Why Option B is Correct:** Vecuronium acts as a competitive antagonist at the **nicotinic acetylcholine receptors ($N_m$)** located on the post-synaptic membrane of the **myoneural (neuromuscular) junction**. By binding to these receptors, it prevents acetylcholine from triggering depolarization, thereby leading to flaccid skeletal muscle paralysis. 2. **Why Other Options are Incorrect:** * **Option A (Cerebral Cortex) & D (Spinal Cord):** Vecuronium is a quaternary ammonium compound, making it highly polar and lipid-insoluble. Consequently, it **does not cross the blood-brain barrier** and has no effect on the Central Nervous System (CNS). It does not provide sedation or analgesia. * **Option C (Muscle Fibres):** The drug acts at the synapse (receptor level) rather than directly on the actin-myosin filaments or the sarcoplasmic reticulum of the muscle fiber itself (unlike Dantrolene, which acts directly on the muscle). **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Vecuronium is primarily excreted via **bile** (60-80%) and partly by the kidneys. It is often preferred in cardiac patients due to its minimal cardiovascular side effects (no histamine release or vagolytic effect). * **Reversal:** Its effects can be reversed using Acetylcholinesterase inhibitors like **Neostigmine** (combined with Glycopyrrolate) or the specific chelating agent **Sugammadex**. * **Comparison:** Unlike Atracurium, Vecuronium does not undergo Hoffman elimination; however, it is safer than Pancuronium in terms of tachycardia.
Question 190: Which drug is not used in the management of glaucoma?
- A. Timolol
- B. Physostigmine
- C. Pilocarpine
- D. Atropine (Correct Answer)
Explanation: **Explanation** The correct answer is **Atropine** because it is a potent **muscarinic antagonist (mydriatic-cycloplegic)**. In the eye, Atropine causes mydriasis (dilation of the pupil) by paralyzing the sphincter pupillae muscle. This leads to the crowding of the iris tissue into the iridocorneal angle, which can obstruct the drainage of aqueous humor through the trabecular meshwork. Consequently, Atropine can precipitate or worsen **acute angle-closure glaucoma** and is strictly contraindicated in such patients. **Analysis of Incorrect Options:** * **Timolol:** A non-selective **beta-blocker** and the first-line treatment for open-angle glaucoma. It works by decreasing the production of aqueous humor from the ciliary body. * **Pilocarpine:** A **miotic (direct cholinergic agonist)**. It causes contraction of the sphincter pupillae and ciliary muscle, which pulls the iris away from the angle and opens the trabecular meshwork, facilitating aqueous drainage. * **Physostigmine:** An **anticholinesterase (indirect cholinergic agonist)**. Like pilocarpine, it induces miosis and improves aqueous outflow; though less commonly used today than prostaglandins or beta-blockers, it remains a valid pharmacological option for glaucoma. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC)** for Acute Angle-Closure Glaucoma: **Acetazolamide** (IV) and **Mannitol** (to rapidly lower IOP), followed by Pilocarpine. * **DOC** for Chronic Open-Angle Glaucoma: **Latanoprost** (PGF2α analog). * **Apraclonidine** is used to prevent IOP spikes after laser trabeculoplasty. * **Atropine Flush:** A side effect of systemic atropine toxicity, characterized by dry, red skin and hyperthermia.
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