Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs

Question 561: Atropine is substituted by phenylephrine to facilitate fundus examination when?

A. Mydriasis required without cycloplegia (Correct Answer)
B. Cycloplegia and mydriasis both are not required
C. Mydriasis and cycloplegia both required
D. Cycloplegia is required

Explanation: ***Mydriasis required without cycloplegia*** - Phenylephrine is a **sympathomimetic** drug that causes **mydriasis (pupil dilation)** by stimulating alpha-1 adrenergic receptors in the iris dilator muscle. - Unlike atropine, phenylephrine has no significant effect on the ciliary muscle, thus it causes minimal to no **cycloplegia (paralysis of accommodation)**, which is ideal if only pupillary dilation is needed for fundus examination without affecting the patient's ability to focus. *Cycloplegia and mydriasis both are not required* - If neither mydriasis nor cycloplegia is required, there would be no need to use phenylephrine or atropine, as the goal is to *facilitate* fundus examination, which typically requires dilation. - This option is incorrect because the question implies a situation where a drug is *substituted* for atropine, indicating a specific need. *Mydriasis and cycloplegia both required* - If both mydriasis and cycloplegia are required, atropine would be the more appropriate choice as it is a potent cycloplegic in addition to being a strong mydriatic. - Phenylephrine does not provide sufficient cycloplegia to meet this requirement. *Cycloplegia is required* - Phenylephrine is a **poor cycloplegic**; its primary action is mydriasis. - If cycloplegia is the main requirement (e.g., for **refraction in children**), drugs like atropine or cyclopentolate would be preferred.

Question 562: Tamsulosin belongs to

A. α1a receptor agonist
B. β-blockers
C. 5α-reductase inhibitors
D. α1a receptor blockers (Correct Answer)

Explanation: ***α1a receptor blockers*** - Tamsulosin is a **selective alpha-1a adrenergic receptor blocker**, which is primarily found in the smooth muscle of the prostate, bladder neck, and urethra. - By blocking these receptors, it causes **relaxation of the smooth muscle**, leading to improved urine flow in conditions like benign prostatic hyperplasia (BPH). *α1a receptor agonist* - An **agonist** would activate the alpha-1a receptors, leading to **contraction of smooth muscle**, which would worsen urinary symptoms in BPH. - This action is contrary to the therapeutic effect of tamsulosin. *β-blockers* - **Beta-blockers** primarily affect the heart and blood vessels by blocking beta-adrenergic receptors and are used for conditions like hypertension or angina. - They do not directly target the alpha-1a receptors in the prostate and would not alleviate BPH symptoms. *5α-reductase inhibitors* - **5-alpha reductase inhibitors** (e.g., finasteride, dutasteride) reduce the size of the prostate by inhibiting the conversion of testosterone to dihydrotestosterone. - They have a different mechanism of action and are used for long-term management of BPH to reduce prostate volume, whereas tamsulosin provides symptomatic relief.

Question 563: The following drug antagonizes the visceral side effects of neostigmine used for reversal of vecuronium blockade:

A. Atropine (Correct Answer)
B. Pilocarpine
C. Pyridostigmine
D. Nicotine

Explanation: ***Atropine*** - **Atropine** is an **anticholinergic drug** that blocks muscarinic receptors, effectively counteracting the **parasympathomimetic side effects** of neostigmine. - When neostigmine is used to reverse neuromuscular blockade, it inhibits **acetylcholinesterase**, increasing acetylcholine levels. This increased acetylcholine stimulates both nicotinic receptors (for muscle contraction) and muscarinic receptors (causing side effects like **bradycardia**, **salivation**, **bronchospasm**, and **gastrointestinal hypermotility**). Atropine selectively blocks these unwanted muscarinic effects. *Pilocarpine* - **Pilocarpine** is a **direct muscarinic agonist**, meaning it would exacerbate, rather than antagonize, the visceral side effects of neostigmine. - It is primarily used to treat **xerostomia** and **glaucoma** by increasing acetylcholine's effects on muscarinic receptors. *Pyridostigmine* - **Pyridostigmine** is another **cholinesterase inhibitor**, similar to neostigmine, and also used for reversal of neuromuscular blockade or in treating **myasthenia gravis**. - It would increase acetylcholine levels and thus enhance, not antagonize, the muscarinic side effects if used with neostigmine in this context. *Nicotine* - **Nicotine** is an agonist primarily acting on **nicotinic acetylcholine receptors**. - While neostigmine increases acetylcholine at nicotinic receptors to reverse muscle blockade, nicotine's primary action is not on muscarinic receptors to counteract the visceral side effects.

Question 564: A 72 year old woman presents with complaints of persistent urinary urgency, and incontinence. Her past medical history is significant for type 2 diabetes, for which she is currently taking glyburide, 5 mg twice daily. Which of the following is the most appropriate treatment for this patient?

A. Bumetanide
B. Oxybutynin (Correct Answer)
C. Neostigmine
D. Metoprolol

Explanation: ***Oxybutynin*** - **Oxybutynin** is an **anticholinergic medication** that reduces bladder muscle spasms and treats symptoms of an **overactive bladder**, such as urgency and incontinence, which are characteristic of this patient's presentation. - It works by blocking muscarinic receptors in the bladder, leading to **detrusor muscle relaxation** and increased bladder capacity. *Bumetanide* - **Bumetanide** is a **loop diuretic** used to treat **edema** and **hypertension** by increasing urine output. - It would worsen urinary incontinence rather than treat it by increasing the frequency and volume of urination. *Neostigmine* - **Neostigmine** is an **acetylcholinesterase inhibitor** used to treat conditions like **myasthenia gravis** or to reverse the effects of neuromuscular blockers. - It increases acetylcholine levels, which would **contract the detrusor muscle** and worsen urinary urgency and incontinence. *Metoprolol* - **Metoprolol** is a **beta-blocker** primarily used to treat **hypertension**, **angina**, and **heart failure**. - It has no direct primary role in treating urinary urgency and incontinence and could potentially exacerbate symptoms in some cases (e.g., in patients with obstructive voiding symptoms).

Question 565: Pilocarpine is used in all of the following except:

A. Primary, Open Angle Glaucoma
B. Acute Angle Closure Glaucoma
C. Malignant Glaucoma (Correct Answer)
D. Chronic Synechial Angle Closure Glaucoma

Explanation: ***Malignant Glaucoma*** - **Pilocarpine** is contraindicated in **malignant glaucoma** because it can worsen the condition by causing **ciliary body edema** and anterior displacement of the lens-iris diaphragm. - This form of glaucoma requires treatment aimed at posterior displacement of the lens-iris diaphragm, often involving **cycloplegics**, **hyperosmotic agents**, or surgical interventions. *Primary, Open Angle Glaucoma* - **Pilocarpine** is an effective **miotic agent** that increases aqueous humor outflow through the **trabecular meshwork**, thereby lowering intraocular pressure. - It can be used as a treatment for **primary open-angle glaucoma**, although it is less commonly used due to its side effects and the availability of better-tolerated medications. *Acute Angle Closure Glaucoma* - **Pilocarpine** is typically used in the management of **acute angle-closure glaucoma** after the intraocular pressure has been acutely lowered by other agents. - It works by inducing **miosis**, which pulls the iris away from the **trabecular meshwork**, opening the angle and facilitating aqueous outflow. *Chronic Synechial Angle Closure Glaucoma* - In **chronic synechial angle-closure glaucoma**, **pilocarpine** can be used to break or prevent the formation of new **peripheral anterior synechiae** by constricting the pupil. - However, its effectiveness is limited if extensive synechiae have already formed, as these physically block the outflow pathway.

Question 566: Which of the following is true of botulinum toxin?

A. It primarily affects the central nervous system
B. It is an endotoxin
C. It inhibits the release of acetylcholine at the neuromuscular junction (Correct Answer)
D. It is a relatively weak neurotoxin

Explanation: ***It inhibits the release of acetylcholine at the neuromuscular junction*** - **Botulinum toxin** acts as a **neurotoxin** that specifically targets the presynaptic terminals of motor neurons. - It cleaves proteins necessary for the fusion of **acetylcholine-containing vesicles** with the presynaptic membrane, thereby preventing acetylcholine release and leading to muscle paralysis. *It primarily affects the central nervous system* - Botulinum toxin **does not readily cross the blood-brain barrier**, and its primary action is at the **peripheral neuromuscular junctions**. - Its effects are largely confined to the **peripheral nervous system**, particularly the somatic motor system. *It is an endotoxin* - **Botulinum toxin** is an **exotoxin**, meaning it is secreted by the bacterium *Clostridium botulinum* into its surroundings. - **Endotoxins** are usually components of the bacterial cell wall (e.g., LPS of gram-negative bacteria) and are released upon cell lysis. *It is a relatively weak neurotoxin* - **Botulinum toxin** is one of the **most potent known toxins**, even in minute quantities. - It is effective at extremely low doses, making it highly dangerous as a contaminant and highly effective in therapeutic applications.

Question 567: Mydriasis is caused by:

A. Horner syndrome
B. Atropine (Correct Answer)
C. Neurosyphilis
D. Organophosphorus poisoning

Explanation: ***Atropine*** - **Atropine** is an **anticholinergic drug** that blocks the action of **acetylcholine** at **muscarinic receptors** in the iris sphincter muscle. - This blockage leads to the relaxation of the **sphincter muscle**, causing **pupil dilation (mydriasis)** and loss of accommodation. *Horner syndrome* - **Horner syndrome** results from damage to the **sympathetic nervous pathway** to the eye. - It classically presents with a triad of **miosis** (constricted pupil), ptosis (drooping eyelid), and **anhydrosis** (decreased sweating) on the affected side. *Neurosyphilis* - **Neurosyphilis** can cause various neurological manifestations, including **Argyll Robertson pupils**. - **Argyll Robertson pupils** are characterized by **small, irregular pupils** that *accommodate but do not react to light* (miosis rather than mydriasis). *Organophosphorus poisoning* - **Organophosphorus compounds** inhibit **acetylcholinesterase**, leading to an excess of acetylcholine at cholinergic synapses. - This overstimulation causes **miosis** (pinpoint pupils), along with other cholinergic symptoms such as salivation, lacrimation, and bradycardia.

Question 568: All of the following are examples of mydriatics except –

A. Tropicamide
B. Atropine
C. Pirenzepine (Correct Answer)
D. Homatropine

Explanation: ***Pirenzepine*** - **Pirenzepine** is an **M1-selective muscarinic antagonist** primarily used to treat peptic ulcers by reducing gastric acid secretion. - It does not significantly affect the **pupil** or cause **mydriasis** as its selectivity is for M1 receptors, which are not predominantly involved in pupillary dilation. *Tropicamide* - **Tropicamide** is a **muscarinic antagonist** that causes rapid and short-acting **mydriasis** and cycloplegia by blocking M3 receptors in the iris sphincter and ciliary body. - It is frequently used for ophthalmic examinations to dilate the pupil. *Atropine* - **Atropine** is a **non-selective muscarinic antagonist** that causes prolonged **mydriasis** and cycloplegia by blocking muscarinic receptors in the eye. - Its effects can last for several days, making it less suitable for routine ophthalmic examinations but useful in treating inflammatory conditions. *Homatropine* - **Homatropine** is a **muscarinic antagonist** with intermediate duration of action, causing **mydriasis** and cycloplegia. - It provides a longer-lasting effect than tropicamide but is shorter than atropine, making it useful in various ophthalmic procedures.

Question 569: Injection of muscarinic agonist in conjunctival sac will lead to all of the following except

A. Miosis
B. Conjunctival and uveal hyperemia
C. Decreased secretion from ciliary epithelium (Correct Answer)
D. Ciliary spasm

Explanation: ***Decreased secretion from ciliary epithelium*** - Muscarinic agonists **do NOT significantly decrease** aqueous humor secretion from the ciliary epithelium. - The primary mechanism for reducing intraocular pressure with drugs like **pilocarpine** is by **increasing outflow** of aqueous humor through the trabecular meshwork via contraction of the ciliary muscle, NOT by decreasing production. - Therefore, "decreased secretion from ciliary epithelium" is the correct answer to this "EXCEPT" question—it does NOT occur with muscarinic agonists. *Miosis* - Muscarinic agonists cause the **pupillary sphincter muscle** (which has M3 receptors) to contract, leading to **pupil constriction** (miosis). - This effect opens the trabecular meshwork and facilitates aqueous humor drainage. *Conjunctival and uveal hyperemia* - Muscarinic agonists cause **vasodilation** in the conjunctival and uveal blood vessels, leading to increased blood flow and **redness** (hyperemia). - This is a common side effect associated with topical application of cholinergic drugs to the eye. *Ciliary spasm* - Muscarinic agonists stimulate the **ciliary muscle** (which has M3 receptors), causing it to contract. - This contraction leads to **accommodation spasm**, resulting in blurred distance vision and brow ache, which is a common adverse effect in younger patients.

Question 570: Anticholinergic which can be used as sedative and antiemetic premedication is

A. Atropine
B. Hyoscine (Correct Answer)
C. Promethazine
D. Glycopyrrolate

Explanation: ***Hyoscine*** - **Hyoscine** (scopolamine) is a muscarinic antagonist that readily crosses the **blood-brain barrier**, allowing it to exert central effects such as **sedation** and potent **antiemetic** actions. - Its ability to reduce secretions and prevent **nausea and vomiting** makes it a suitable anticholinergic for premedication. *Atropine* - **Atropine** is primarily used to increase **heart rate**, reduce **salivary and bronchial secretions**, and as an antidote for cholinesterase inhibitors. - While it is an anticholinergic, its central effects are less pronounced at clinical doses compared to hyoscine, making it less suitable as a sole sedative or antiemetic. *Promethazine* - **Promethazine** is an antihistamine with significant **anticholinergic, sedative**, and **antiemetic** properties. - However, it is primarily classified as an **H1-receptor antagonist** rather than a pure anticholinergic for premedication, although it is often used for these effects. *Glycopyrrolate* - **Glycopyrrolate** is a quaternary ammonium anticholinergic that does not readily cross the **blood-brain barrier**. - Its action is largely peripheral, making it effective for reducing secretions but without significant **sedative** or **antiemetic** effects.

Practice by Chapter

Cholinergic Agonists

Practice Questions

Cholinergic Antagonists

Practice Questions

Adrenergic Agonists

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Adrenergic Antagonists

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Ganglionic Agents

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Neuromuscular Blocking Agents

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Autonomic Drugs in Ophthalmology

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Autonomic Drugs in Cardiovascular Disease

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Autonomic Drugs in Respiratory Disease

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Autonomic Drugs in Urological Disorders

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