Autonomic Nervous System Drugs Practice Questions

Q: Which antimuscarinic drug is used in overactive bladder?

Trospium. ***Trospium*** - **Trospium** is a quaternary ammonium compound that acts as an **antimuscarinic agent** primarily used to treat **overactive bladder (OAB)**. - Its **polar nature** limits its ability to cross the blood-brain barrier, reducing central nervous system side effects common with other antimuscarinics. *Tropicamide* - **Tropicamide** is an **antimuscarinic** agent primarily used as a **mydriatic** (to dilate pupils) and **cycloplegic** (to paralyze the ciliary muscle) for ophthalmic examinations. - It has a short duration of action, making it unsuitable for chronic conditions like overactive bladder. *Atropine* - **Atropine** is a non-selective **muscarinic antagonist** with a wide range of uses, including bradycardia, organophosphate poisoning, and ophthalmic procedures. - While it has antimuscarinic effects on the bladder, its systemic side effects (e.g., dry mouth, blurred vision, tachycardia) limit its use for overactive bladder. *Pirenzepine* - **Pirenzepine** is a selective **M1 muscarinic antagonist** primarily used to treat **peptic ulcers** by reducing gastric acid secretion. - Its selectivity for M1 receptors means it has limited efficacy for relieving bladder symptoms, which are primarily mediated by M2 and M3 receptors.

Q: Which is the longest acting anti-cholinesterase?

Echothiophate. ***Echothiophate*** - **Echothiophate** is an **organophosphate** compound that irreversibly inhibits acetylcholinesterase, leading to a prolonged duration of action, often measured in weeks. - Due to its **long-acting** and irreversible nature, it is primarily used in ophthalmic preparations for glaucoma but is not commonly used systemically. *Pyridostigmine* - **Pyridostigmine** is a medium-acting anticholinesterase, typically lasting **3-6 hours**, and is commonly used for the chronic management of **myasthenia gravis**. - Its effects are **reversible**, binding to the enzyme for a limited period. *Ambenonium* - **Ambenonium** has a longer duration of action than pyridostigmine, typically lasting **4-8 hours**, but is still considered a reversible inhibitor. - It was historically used for **myasthenia gravis** but is now less common due to the availability of other effective treatments. *Edrophonium* - **Edrophonium** is a very short-acting anticholinesterase, with effects lasting only **5-15 minutes**, making it ideal for the **Tensilon test** to diagnose myasthenia gravis and differentiate between myasthenic and cholinergic crises. - Its rapid onset and brief duration are due to its **reversible** and transient binding to acetylcholinesterase.

Q: Maximum cycloplegic action of atropine is seen at ?

1-3 hours. ***1-3 hours*** - Atropine, a **non-selective muscarinic antagonist**, reaches its **peak cycloplegic effect** approximately 1 to 3 hours after topical administration. - This peak activity is crucial for accurate retinoscopy and **refractive error measurement** in children, as it effectively paralyzes the ciliary muscle. *4-6 hours* - While atropine's cycloplegic effect is still present at 4-6 hours, it is generally **past its peak action** by this time. - Slower-acting cycloplegics might have their peak around this window, but not atropine. *1-2 weeks* - The **duration of action** for atropine's cycloplegic and mydriatic effects can last for 1-2 weeks, but this is the total duration, not when the maximum action is observed. - Patients are often instructed about the **prolonged effects** and potential for blurred vision and photophobia over this period. *30-60 minutes* - While some mydriatic effects might start within 30-60 minutes, the **full cycloplegic effect** of atropine, which requires maximum paralysis of the ciliary muscle, is not achieved in this short timeframe. - Shorter-acting cycloplegics like **cyclopentolate** or **tropicamide** would show peak action within this earlier interval.

Q: Which of the following is NOT a side effect of atropine?

Diarrhoea. ***Diarrhoea*** - Atropine is a **muscarinic antagonist** that blocks the action of **acetylcholine** on muscarinic receptors in the gastrointestinal tract. - This leads to **decreased GI motility** and **decreased secretions**, typically causing **constipation**, NOT diarrhoea. - Diarrhoea would be associated with **cholinergic agonists** or anticholinesterases, which increase GI motility. *Blurring of vision* - Atropine causes **mydriasis** (pupil dilation) and **cycloplegia** (paralysis of the ciliary muscle). - **Cycloplegia** impairs accommodation for near vision, leading to **blurring of vision**. - This is a common anticholinergic side effect. *Urinary retention* - Atropine blocks **M3 receptors** on the **detrusor muscle**, causing bladder relaxation and reduced contractility. - This leads to **urinary retention**, especially in patients with pre-existing conditions like **prostatic hypertrophy**. *Confusion in elderly* - Atropine can cross the **blood-brain barrier** and cause **CNS effects** including confusion, agitation, and delirium. - Elderly patients are particularly susceptible to these **central anticholinergic effects**.

Q: Which of the following is an action of muscarinic cholinergic receptors?

Decreased heart rate. ***Decreased heart rate*** - Activation of **muscarinic cholinergic receptors (M2 receptors)** in the heart leads to a decrease in heart rate and conduction velocity. - This effect is mediated by the **vagus nerve (parasympathetic nervous system)**, which releases acetylcholine to act on these receptors. - This is the **most characteristic and clinically significant cardiovascular effect** of muscarinic receptor activation, making it the expected answer. *Skeletal muscle contraction* - **Skeletal muscle contraction** is mediated by **nicotinic acetylcholine receptors (nAChRs)** at the **neuromuscular junction**, NOT muscarinic receptors. - Nicotinic receptors are **ligand-gated ion channels** that cause direct depolarization and muscle contraction when activated. - This is the only option that is **NOT a muscarinic receptor action**. *Acid secretion in stomach* - **Gastric acid secretion** IS mediated by **M3 muscarinic receptors** on parietal cells. - Acetylcholine from the vagus nerve directly stimulates parietal cells and also stimulates histamine release from enterochromaffin-like cells. - While this is a valid muscarinic action, in the context of distinguishing muscarinic effects, **cardiac effects** (decreased heart rate) are more emphasized as the classic teaching point. *Salivation and lacrimation* - **Salivation and lacrimation** ARE mediated by **M3 muscarinic receptors** in exocrine glands. - These are classic parasympathetic/muscarinic effects taught in physiology. - However, when distinguishing key muscarinic actions, **M2 receptor-mediated cardiac effects** are typically highlighted as the primary cardiovascular manifestation, while M3 effects on glands are secondary teaching points.

Q: Which anti-cholinesterase drug is known for its central nervous system activity?

Physostigmine. ***Physostigmine*** - Unlike most other anti-cholinesterases, **physostigmine** is a **tertiary amine** and is relatively lipid-soluble, allowing it to cross the **blood-brain barrier**. [2] - Its ability to increase acetylcholine in the CNS makes it useful in treating anticholinergic toxicity (e.g., atropine overdose). [2] *Pyridostigmine* - **Pyridostigmine** is a **quaternary amine** and does not readily cross the blood-brain barrier, primarily acting peripherally. - It is mainly used in the long-term management of **myasthenia gravis**. *Edrophonium* - **Edrophonium** is a very short-acting **quaternary amine** that does not cross the blood-brain barrier. [1] - It is primarily used for the **diagnosis of myasthenia gravis** (Tensilon test) due to its rapid onset and short duration of action. [1] *Neostigmine* - **Neostigmine** is also a **quaternary amine** with poor lipid solubility, meaning it has minimal central nervous system activity. [2] - It is commonly used to reverse the effects of **non-depolarizing neuromuscular blockers** and in the treatment of **myasthenia gravis**.

Q: Which drug is used for sympathectomy in experimental animals?

Guanethidine. ***Guanethidine*** - **Guanethidine** is a potent **adrenergic neuron blocking drug** that is taken up by noradrenergic neurons and prevents the release of norepinephrine, leading to a chemical sympathectomy. - In experimental animal models, it is used to induce a **pharmacological sympathectomy** to study the effects of sympathetic nervous system blockade on various physiological processes. *Atropine* - **Atropine** is a **muscarinic acetylcholine receptor antagonist** that blocks the effects of acetylcholine at parasympathetic postganglionic terminals. - It is primarily used to block **parasympathetic responses**, not sympathetic ones, and therefore would not induce a sympathectomy. *Diazoxide* - **Diazoxide** is a direct **arteriolar vasodilator** that works by opening potassium channels in vascular smooth muscle. - It is used to quickly reduce blood pressure in **hypertensive emergencies** and for treating hypoglycemia due to insulin oversecretion, and does not cause sympathectomy. *Thebaine* - **Thebaine** is an **opioid alkaloid** found in opium, structurally similar to morphine and codeine, but with primarily stimulatory rather than depressant effects. - It acts as a **convulsant** and is used as a precursor in the synthesis of other opioids, but has no role in causing sympathectomy.

Q: Beta2-agonists cause all except:

Hyperkalemia. ***Hyperkalemia*** - Beta2-agonists actually cause **hypokalemia**, not hyperkalemia, by promoting the intracellular shift of potassium. - This effect is due to the stimulation of the **Na+/K+-ATPase pump** by beta-2 adrenergic receptors. *Hyperglycemia* - Beta2-agonists can lead to **hyperglycemia** by promoting glycogenolysis and gluconeogenesis in the liver. - They also decrease **insulin secretion** and increase insulin resistance. *Tremor* - **Tremor** is a common side effect of beta2-agonists, particularly in the hands, due to direct stimulation of beta2 receptors on skeletal muscle. - This muscle stimulation leads to increased muscle twitching and a fine tremor. *Palpitation* - **Palpitations** can occur due to the systemic absorption of beta2-agonists, leading to activation of beta1 receptors in the heart. - This can cause **tachycardia** and a sensation of a racing heart.

Q: What is the drug of choice for pheochromocytoma?

Phenoxybenzamine. ***Phenoxybenzamine*** - This is an **irreversible, non-selective alpha-adrenergic blocker**, which is the drug of choice for preparing patients for surgical removal of a pheochromocytoma. - It effectively controls **hypertension** by blocking the effects of catecholamines on blood vessels, preventing a hypertensive crisis during surgery. *Propranolol* - **Beta-blockers** like propranolol should **not be used as monotherapy** in pheochromocytoma because blocking beta-2 receptors without prior alpha blockade can lead to unopposed alpha-adrenergic vasoconstriction and precipitate a **hypertensive crisis**. - It can be added **after adequate alpha-blockade** to control tachycardia. *Prazosin* - Prazosin is a **reversible, selective alpha-1 adrenergic blocker**, which is not preferred over phenoxybenzamine due to its shorter duration of action and reversibility. - While it can lower blood pressure, its efficacy in preventing hypertensive crises during surgery for pheochromocytoma is **less robust** compared to phenoxybenzamine. *Nitroprusside* - Sodium nitroprusside is a **potent vasodilator** often used for **hypertensive emergencies**, but it is not the drug of choice for long-term management or preoperative preparation in pheochromocytoma. - Its use in pheochromocytoma is typically reserved for **acute hypertensive crises** when other agents are insufficient, rather than initial management.

Q: Botulinum toxin type B is used in which disease?

Cervical dystonia. ***Cervical dystonia*** * **Botulinum toxin type B (Myobloc/NeuroBloc)** is specifically approved for the treatment of **cervical dystonia**, which involves involuntary contractions of neck muscles. * It works by blocking the release of **acetylcholine** at the neuromuscular junction, leading to muscle relaxation. *Strabismus* * **Botulinum toxin type A (Botox, Dysport, Xeomin)** is the preferred and most commonly used form for treating **strabismus** by temporarily weakening specific extraocular muscles. * Type B is generally not indicated for strabismus due to differences in potency and duration of action. *Blepharospasm* * **Botulinum toxin type A** (e.g., Botox) is the primary treatment for **blepharospasm**, an involuntary forceful closure of the eyelids. * While both types inhibit acetylcholine release, type A has a more established and concentrated use in treating localized muscle spasms like blepharospasm. *Glabellar lines* * **Botulinum toxin type A** is widely used for cosmetic applications such as reducing **glabellar lines** (frown lines between the eyebrows). * Its efficacy and safety for cosmetic indications are well-established, making type A the standard choice over type B.

Question 1

Which antimuscarinic drug is used in overactive bladder?

Accepted Answer

Trospium

Answer

Atropine

Answer

Tropicamide

Answer

Pirenzepine

Question 2

Which is the longest acting anti-cholinesterase?

Accepted Answer

Echothiophate

Answer

Pyridostigmine

Answer

Ambenonium

Answer

Edrophonium

Question 3

Maximum cycloplegic action of atropine is seen at ?

Accepted Answer

1-3 hours

Answer

1-2 weeks

Answer

4-6 hours

Answer

30-60 minutes

Question 4

Which of the following is NOT a side effect of atropine?

Accepted Answer

Diarrhoea

Answer

Urinary retention

Answer

Confusion of elderly

Answer

Blurring of vision

Question 5

Which of the following is an action of muscarinic cholinergic receptors?

Accepted Answer

Decreased heart rate

Answer

Skeletal muscle contraction

Answer

Acid secretion in stomach

Answer

Salivation and lacrimation

Question 6

Which anti-cholinesterase drug is known for its central nervous system activity?

Accepted Answer

Physostigmine

Answer

Edrophonium

Answer

Pyridostigmine

Answer

Neostigmine

Question 7

Which drug is used for sympathectomy in experimental animals?

Accepted Answer

Guanethidine

Answer

Atropine

Answer

Diazoxide

Answer

Thebaine

Question 8

Beta2-agonists cause all except:

Accepted Answer

Hyperkalemia

Answer

Hyperglycemia

Answer

Tremor

Answer

Palpitation

Question 9

What is the drug of choice for pheochromocytoma?

Accepted Answer

Phenoxybenzamine

Answer

Propranolol

Answer

Prazosin

Answer

Nitroprusside

Question 10

Botulinum toxin type B is used in which disease?

Accepted Answer

Cervical dystonia

Answer

Blepharospasm

Answer

Strabismus

Answer

Glabellar lines

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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