Autonomic Nervous System Drugs Practice Questions

Q: Which drug can exhibit Phase II neuromuscular block:

Scoline. ***Scoline*** - **Scoline** (**succinylcholine**) is a depolarizing neuromuscular blocker that can cause a **Phase II block** with prolonged or high-dose administration. - In a Phase II block, the neuromuscular junction becomes desensitized to acetylcholine, leading to a block that resembles a **non-depolarizing block**, including fade and post-tetanic potentiation. *Cocaine* - **Cocaine** is a local anesthetic and a stimulant; it primarily acts by blocking the reuptake of **norepinephrine**, **dopamine**, and **serotonin** in the central nervous system. - It does not directly affect the neuromuscular junction to cause a depolarizing or Phase II block. *Vencuronium, ether, N2O* - **Vencuronium** is a **non-depolarizing neuromuscular blocker** that produces a competitive block at the neuromuscular junction, which is distinct from a Phase II block. - **Ether** is an inhaled anesthetic that can cause muscle relaxation but does not typically induce a Phase II neuromuscular block. **N2O** (nitrous oxide) is a weak anesthetic with no significant neuromuscular blocking properties. *D-TC* - **d-tubocurarine (d-TC)** is a **non-depolarizing neuromuscular blocker** that competitively antagonizes acetylcholine at the nicotinic receptors. - Unlike scoline, it does not cause initial depolarization or a subsequent Phase II block.

Q: You are in the eye OPD and wish to use a topical Beta blocker in a patient. The chosen drug by you should have all the following properties except

Strong local anaesthetic activity. ***Strong local anaesthetic activity*** - Topical beta blockers for glaucoma should **not possess significant local anesthetic activity** as this property is not related to their mechanism of action in lowering intraocular pressure and could lead to unwanted corneal effects or masking of pain. - Their primary role is to **reduce aqueous humor production** by blocking beta-adrenergic receptors on the ciliary epithelium. *High ocular capture* - **High ocular capture** (good penetration into the eye) is a desirable property for topical eye medications, ensuring sufficient drug concentration at the target tissues (e.g., ciliary body) to exert its therapeutic effect. - This property allows the drug to effectively inhibit aqueous humor production and **lower intraocular pressure**. *High lipophilicity* - **High lipophilicity** is beneficial for topical ophthalmic drugs as it enhances their ability to **cross lipid-rich corneal barriers** and reach the aqueous humor and ciliary body. - This property contributes to improved drug penetration and overall **ocular bioavailability**. *Low Systemic activity* - **Low systemic activity** is a crucial characteristic for topical ophthalmic drugs, especially beta blockers, to minimize systemic side effects such as **bradycardia**, **bronchospasm**, or **hypotension**. - Systemic absorption is reduced by limiting drug access to the general circulation, for example, by **nasolacrimal occlusion**.

Q: Which of the following is false about drugs given in urinary incontinence

Tolterodine can be given as transdermal patch. ***Tolterodine can be given as transdermal patch*** - This statement is **false**. While tolterodine is available in oral forms, such as extended-release capsules, it is **not available as a transdermal patch**. - **Oxybutynin** is the muscarinic antagonist commonly available and administered as a transdermal patch for urinary incontinence. *Oxybutynin, Tolterodine, and Solifenacin are muscarinic receptor blockers used to decrease detrusor muscle contraction* - This statement is **true**; these drugs are indeed anticholinergics that block muscarinic receptors (primarily M3) on the detrusor muscle. - By blocking these receptors, they reduce the involuntary contractions of the detrusor, thereby alleviating symptoms of **overactive bladder** and urgency incontinence. *Darifenacin is a selective M3 antagonist* - This statement is **true**; **darifenacin** is known for its high selectivity for the **M3 muscarinic receptor**. - This selectivity makes it effective in treating **overactive bladder** with potentially fewer side effects in other organ systems compared to less selective anticholinergics. *Trospium is a quaternary amine with no CNS side effects* - This statement is **true**; **trospium** is a **quaternary amine**, which means it has a permanent positive charge. - Due to its charge, it has **poor lipid solubility** and does not readily cross the **blood-brain barrier**, resulting in a significantly lower incidence of central nervous system (CNS) side effects compared to tertiary amines.

Q: All of the following drugs are used for the treatment of urinary incontinence except:

Ipratropium. ***Ipratropium*** - **Ipratropium** is a short-acting muscarinic antagonist primarily used as a **bronchodilator** in obstructive lung diseases. - While it has anticholinergic properties, it is not typically used for **urinary incontinence** due to its limited systemic absorption and short duration of action, making it less effective for bladder control compared to other agents. *Oxybutynin* - **Oxybutynin** is a commonly prescribed **muscarinic antagonist** that acts by relaxing the bladder detrusor muscle, increasing bladder capacity and reducing involuntary contractions. - It is effective in treating **overactive bladder** and urge incontinence. *Tolterodine* - **Tolterodine** is a **muscarinic receptor antagonist** that specifically targets M2 and M3 receptors in the bladder, reducing bladder hyperreactivity. - It is used for the symptomatic treatment of **urge incontinence** and overactive bladder. *Darifenacin* - **Darifenacin** is a highly M3-selective muscarinic receptor antagonist, which means it primarily blocks the M3 receptors responsible for **detrusor muscle contraction**. - Its selectivity helps minimize side effects common to less selective anticholinergics and is used for the treatment of **overactive bladder** with symptoms of urgency, frequency, and urge incontinence.

Q: An elderly male on ventilator has received atracurium infusion for 3 days. He now develops epileptic fits. Probable cause for his epilepsy is:

Accumulation of Laudanosine. Accumulation of Laudanosine\n - Atracurium is metabolized in the body via Hofmann elimination and ester hydrolysis into laudanosine and other inactive metabolites.\n - Laudanosine is a tertiary amine that can cross the blood-brain barrier and, at high concentrations, is a CNS stimulant, potentially inducing seizures.\n\nVentilator failure\n - Ventilator failure would lead to respiratory distress and potentially hypoxia, which can cause seizures, but it's not a direct pharmacological effect of atracurium or its metabolites.\n - The question implies a drug-related cause due to prolonged atracurium infusion, making ventilator failure less likely as the probable cause for drug-induced epilepsy.\n\nAccumulation of Atracurium\n - While prolonged infusion of atracurium means continuous drug administration, atracurium itself does not typically accumulate to toxic levels in the same way as its metabolites, especially in patients with normal organ function, due to its organ-independent elimination.\n - Atracurium is a neuromuscular blocker and its accumulation would primarily lead to prolonged paralysis, not directly to epileptic fits.\n\nAllergy to drug\n - An allergic reaction to a drug typically manifests as rash, anaphylaxis, or bronchospasm, not primarily as epileptic fits, unless severe anaphylaxis leads to cerebral hypoperfusion and secondary seizure.\n - While possible, it is not the most common or direct cause of seizures associated with atracurium administration.

Q: All of the following drugs cross the blood-brain barrier, EXCEPT:

Neostigmine. ***Neostigmine*** - As a **quaternary ammonium compound**, neostigmine carries a permanent positive charge, making it highly **hydrophilic** and unable to readily cross the **blood-brain barrier (BBB)**. - Its inability to cross the BBB means its effects are primarily limited to the **peripheral nervous system**, particularly at the neuromuscular junction for conditions like myasthenia gravis, or in the gut for paralytic ileus. *Physostigmine* - Physostigmine is a **tertiary amine** that is **lipid-soluble** at physiological pH, allowing it to easily cross the **blood-brain barrier** and exert central nervous system effects. - It is used to treat **central anticholinergic syndrome** because it can reverse the central effects of anticholinergic drugs. *Atropine* - Atropine is a **tertiary amine** that is also **lipid-soluble** and readily crosses the **blood-brain barrier**, leading to significant central nervous system effects such as sedation, excitation, or even delirium at higher doses. - Its ability to cross the BBB contributes to its wide range of systemic anticholinergic effects, including those on the brain. *Lignocaine* - Lignocaine (lidocaine) is a **tertiary amine local anesthetic** that is highly **lipid-soluble** and can readily cross the **blood-brain barrier**. - Its entry into the CNS is responsible for its potential side effects such as **seizures, dizziness, and central nervous system depression** when absorbed systemically.

Q: Succinylcholine causes hyperkalemia in patients with -

All of the options. ***All of the options*** - **Succinylcholine** can cause dangerous **hyperkalemia** due to upregulation of **extrajunctional acetylcholine receptors** on muscle cell membranes, leading to exaggerated potassium efflux upon depolarization [1]. - This occurs in conditions causing **muscle denervation** or **prolonged disuse** [1], [2]. *Major trauma with crush injury* - Patients with **severe trauma** involving **crush injuries** or extensive muscle damage develop receptor upregulation within 24-48 hours [1]. - The trauma causes muscle **denervation** and damage, leading to proliferation of acetylcholine receptors across the muscle membrane [1]. - Risk persists for weeks to months after injury. *Burns* - Patients with **major burns** (typically >10% total body surface area) develop marked upregulation of **extrajunctional acetylcholine receptors** in damaged and regenerating muscle tissue [1], [2]. - Risk begins **24-48 hours post-burn** and can persist for **months to years**. - This is one of the **most well-established contraindications** to succinylcholine use [2]. *Prolonged immobilization* - **Extended bed rest**, **ICU immobilization**, or **prolonged casting** leads to disuse-induced upregulation of acetylcholine receptors. - Risk typically develops after **5-7 days** of immobilization and persists throughout the immobilization period [2]. - Includes patients with paraplegia, quadriplegia, or prolonged mechanical ventilation [2].

Q: Which is the shortest-acting mydriatic?

Tropicamide. ***Tropicamide*** - It is an **anticholinergic drug** that produces **mydriasis** (pupil dilation) due to its blocking effect on **muscarinic receptors** in the iris sphincter muscle. - Tropicamide has the **shortest duration of action** among the listed mydriatic agents, typically lasting 4-6 hours. *Homatropine* - Homatropine is an **anticholinergic drug** with a longer duration of action than tropicamide, typically lasting 1-3 days. - It is commonly used for **cycloplegia** and mydriasis in ophthalmology, but not as the shortest-acting agent. *Atropine* - Atropine is a potent **anticholinergic drug** with the **longest duration of action**, causing mydriasis and cycloplegia that can last for 7-14 days. - Due to its prolonged effects, it is less commonly used for routine pupil dilation and more for therapeutic purposes like treating **anterior uveitis**. *Cyclopentolate* - Cyclopentolate is an **anticholinergic agent** that causes mydriasis and cycloplegia with a duration of action of approximately 6-24 hours. - While faster acting than atropine and homatropine, it is still longer-acting than tropicamide.

Q: Which of the following is not a side effect of topical beta blockers?

Heterochromia iridis. ***Heterochromia iridis*** - **Heterochromia iridis** (different colored irises) is a well-known side effect of **prostaglandin analogs** (e.g., latanoprost, bimatoprost), not topical beta blockers. - This change in eye color occurs due to increased **melanin production** in melanocytes. *Asthma* - Topical beta blockers can be absorbed systemically and block **beta-2 receptors** in the lungs, leading to **bronchoconstriction** and exacerbating **asthma**. - This side effect is particularly concerning in patients with a history of **reactive airway disease**. *Hypoglycemia* - Topical beta blockers are listed as a concern for **hypoglycemia risk** because they **mask the adrenergic symptoms of hypoglycemia** (tremor, palpitations, tachycardia). - While they don't directly cause hypoglycemia, masking these warning symptoms can lead to **delayed recognition and treatment**, particularly dangerous in **diabetic patients on insulin or sulfonylureas**. *Bradycardia* - Systemic absorption of topical beta blockers can lead to a decrease in **heart rate** (bradycardia) by blocking **beta-1 receptors** in the heart. - This effect is a significant concern for patients with pre-existing **cardiac conduction disorders** or those taking other medications that lower heart rate.

Q: All of the following are cycloplegics except :

Phenylephrine. ***Phenylephrine*** - **Phenylephrine** is a **sympathomimetic** agent that primarily acts as a **mydriatic** (dilates the pupil) by stimulating the **alpha-1 adrenergic receptors** in the iris dilator muscle [1], [2]. - It has **absolutely no cycloplegic effect**, meaning it does not paralyze the ciliary muscle or affect accommodation at all [1]. - This makes it the **only pure mydriatic** among the options, with zero cycloplegic action [3]. *Atropine* - **Atropine** is a potent **anticholinergic** agent that blocks **muscarinic receptors** in the ciliary body, causing **strong cycloplegia** (paralysis of accommodation) [1], [4]. - Duration of cycloplegia: **7-14 days**, making it the longest-acting cycloplegic. - Also causes mydriasis by paralyzing the iris sphincter muscle. *Cocaine* - **Cocaine** is a **local anesthetic** and **sympathomimetic** that inhibits norepinephrine reuptake, causing **mydriasis** [2]. - Unlike phenylephrine, cocaine can produce **weak cycloplegic effects** through its local anesthetic action and sympathetic stimulation, though much less than anticholinergics. - Primarily used diagnostically in ophthalmology (e.g., Horner's syndrome testing) [2]. - Since it does have some cycloplegic effect (albeit minimal), it is technically a cycloplegic, making **phenylephrine the correct answer** as the only drug with no cycloplegia at all. *Homatropine* - **Homatropine** is an **anticholinergic** agent with **moderate cycloplegic** potency. - Duration: **1-3 days** (shorter than atropine, longer than tropicamide). - Blocks **muscarinic receptors** in the ciliary body, causing cycloplegia and mydriasis.

Question 1

Which drug can exhibit Phase II neuromuscular block:

Accepted Answer

Scoline

Answer

Cocaine

Answer

D-TC

Answer

Vencuronium, ether, N2O

Question 2

You are in the eye OPD and wish to use a topical Beta blocker in a patient. The chosen drug by you should have all the following properties except

Accepted Answer

Strong local anaesthetic activity

Answer

High ocular capture

Answer

High lipophilicity

Answer

Low Systemic activity

Question 3

Which of the following is false about drugs given in urinary incontinence

Accepted Answer

Tolterodine can be given as transdermal patch

Answer

Oxybutynin, Tolterodine, and Solifenacin are muscarinic receptor blockers used to decrease detrusor muscle contraction

Answer

Darifenacin is a selective M3 antagonist

Answer

Trospium is a quaternary amine with no CNS side effects

Question 4

All of the following drugs are used for the treatment of urinary incontinence except:

Accepted Answer

Ipratropium

Answer

Oxybutynin

Answer

Tolterodine

Answer

Darifenacin

Question 5

An elderly male on ventilator has received atracurium infusion for 3 days. He now develops epileptic fits. Probable cause for his epilepsy is:

Accepted Answer

Accumulation of Laudanosine

Answer

Ventilator failure

Answer

Accumulation of Atracurium

Answer

Allergy to drug

Question 6

All of the following drugs cross the blood-brain barrier, EXCEPT:

Accepted Answer

Neostigmine

Answer

Physostigmine

Answer

Atropine

Answer

Lignocaine

Question 7

Succinylcholine causes hyperkalemia in patients with -

Accepted Answer

All of the options

Answer

Major trauma with crush injury

Answer

Burns

Answer

Prolonged immobilization

Question 8

Which is the shortest-acting mydriatic?

Accepted Answer

Tropicamide

Answer

Homatropine

Answer

Atropine

Answer

Cyclopentolate

Question 9

Which of the following is not a side effect of topical beta blockers?

Accepted Answer

Heterochromia iridis

Answer

Asthma

Answer

Hypoglycemia

Answer

Bradycardia

Question 10

All of the following are cycloplegics except :

Accepted Answer

Phenylephrine

Answer

Atropine

Answer

Cocaine

Answer

Homatropine

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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