Neuromuscular Blocking Agents — MCQs
A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery?
Non-depolarizing neuromuscular blocker is characterized by
The anaesthesia of choice in renal disease is which one of the following:
In pseudocholinesterase deficiency, which drug should be used cautiously?
The reversal by sugammadex is possible with all the following neuromuscular blocker except-
Which drug can exhibit Phase II neuromuscular block:
Mechanism of action of curare-like drugs?
Hippus occurs in which poisoning?
Which of the following is not a recognized use of alpha-2-agonists?
Which sympathomimetic drug is primarily known to increase heart rate?
Neuromuscular Blocking Agents Indian Medical PG Practice Questions and MCQs
Question 1: A person was given a muscle relaxant that competitively blocks nicotinic receptors. Which of the following drugs is used for reversal of muscle relaxation after surgery?
- A. Carbachol
- B. Succinylcholine
- C. Physostigmine
- D. Neostigmine (Correct Answer)
Explanation: ***Neostigmine*** - **Neostigmine** is an **acetylcholinesterase inhibitor** that increases the amount of acetylcholine at the neuromuscular junction, thereby overcoming the competitive block at nicotinic receptors [1], [4]. - This increase in acetylcholine effectively reverses the paralysis caused by **nondepolarizing muscle relaxants**, making it useful for post-surgical recovery [2]. *Carbachol* - **Carbachol** is a **direct-acting cholinergic agonist** that stimulates both muscarinic and nicotinic receptors and is not typically used for reversing competitive neuromuscular blockade. - Its primary use is for glaucoma and to stimulate the bladder or bowels, not to counteract muscle relaxants. *Succinylcholine* - **Succinylcholine** is a **depolarizing muscle relaxant** and would prolong, rather than reverse, muscle blockade if administered after a competitive blocker [3]. - It works by initially causing depolarization and then preventing further muscle contraction, leading to paralysis. *Physostigmine* - **Physostigmine** is an **acetylcholinesterase inhibitor** that crosses the blood-brain barrier, making it more suitable for treating central anticholinergic toxicity rather than peripheral neuromuscular blockade. - While it inhibits acetylcholinesterase, its central effects and potential for seizures limit its use for reversing surgical muscle relaxation.
Question 2: Non-depolarizing neuromuscular blocker is characterized by
- A. Non competitive neuromuscular blocker
- B. Reversed by neostigmine (Correct Answer)
- C. Induces fasciculations
- D. Persistent stimulator of nicotinic cholinergic receptors
Explanation: ***Reversed by neostigmine*** - **Non-depolarizing neuromuscular blockers** are **competitive antagonists** at the **nicotinic acetylcholine receptors** at the neuromuscular junction. - **Neostigmine** is an **acetylcholinesterase inhibitor** that increases the concentration of acetylcholine in the synaptic cleft, thereby overcoming the competitive blockade. *Non competitive neuromuscular blocker* - Non-depolarizing neuromuscular blockers are, by definition, **competitive antagonists** at the **nicotinic acetylcholine receptors**. - A non-competitive blocker would bind to a different site on the receptor or an allosteric site to produce its effect. *Induces fasciculations* - **Fasciculations** (visible muscle twitching) are characteristic of **depolarizing neuromuscular blockers** like **succinylcholine**, as they initially activate the receptors before causing prolonged depolarization and paralysis. - Non-depolarizing blockers do not typically cause fasciculations because they prevent acetylcholine from binding and activating the receptors. *Persistent stimulator of nicotinic cholinergic receptors* - This describes the mechanism of action of **depolarizing neuromuscular blockers** like **succinylcholine**, which persistently activate the receptor, leading to initial fasciculations followed by sustained depolarization and paralysis. - **Non-depolarizing blockers** act as **antagonists**, preventing activation of the receptors.
Question 3: The anaesthesia of choice in renal disease is which one of the following:
- A. Atracurium
- B. Cisatracurium (Correct Answer)
- C. Vecuronium
- D. Rocuronium
Explanation: ***Cisatracurium*** - **Cisatracurium** is preferred in renal disease because it undergoes **Hofmann elimination**, a chemical breakdown independent of renal or hepatic function. - Its metabolism generates **laudanosine**, a metabolite that can accumulate in renal failure but has minimal clinical significance at typical doses. *Atracurium* - **Atracurium** also undergoes **Hofmann elimination** and ester hydrolysis, making it suitable for renal patients, but it produces more **laudanosine** than cisatracurium. - Higher levels of **laudanosine** can potentially cause central nervous system excitation (seizures) with prolonged use or in very high doses, although this is rare in clinical practice. *Vecuronium* - **Vecuronium** is primarily eliminated by the **liver** and, to a lesser extent, by the kidneys, so its duration of action can be prolonged in renal failure. - Its active metabolites, particularly **3-desacetylvecuronium**, accumulate significantly in renal insufficiency, leading to prolonged neuromuscular blockade. *Rocuronium* - **Rocuronium** is mainly eliminated by the **liver** (approximately 70-80%), with a smaller portion excreted renally. - In patients with renal failure, its duration of action can be significantly prolonged due to reduced renal clearance and potential alterations in hepatic elimination.
Question 4: In pseudocholinesterase deficiency, which drug should be used cautiously?
- A. Succinylcholine (Correct Answer)
- B. Barbiturates
- C. Gallamine
- D. Halothane
Explanation: ***Succinylcholine*** - **Succinylcholine** is primarily metabolized by **pseudocholinesterase** (also known as butyrylcholinesterase). - In individuals with **pseudocholinesterase deficiency**, the metabolism of succinylcholine is significantly delayed, leading to **prolonged neuromuscular blockade** and extended paralysis. *Barbiturates* - **Barbiturates** are mainly metabolized by the **hepatic cytochrome P450 system** and do not depend on pseudocholinesterase for their breakdown. - Their metabolism would not be significantly affected by pseudocholinesterase deficiency. *Halothane (an inhalational anesthetic)* - **Halothane** is primarily metabolized by the **hepatic cytochrome P450 system** and excreted via the lungs. - Its metabolism is unrelated to **pseudocholinesterase activity**. *Gallamine (a neuromuscular blocker)* - **Gallamine** is a **nondepolarizing neuromuscular blocker** that is primarily eliminated by **renal excretion** as an unchanged drug. - Its metabolism and elimination are independent of **pseudocholinesterase**.
Question 5: The reversal by sugammadex is possible with all the following neuromuscular blocker except-
- A. Vecuronium
- B. Atracurium (Correct Answer)
- C. Pancuronium
- D. Rocuronium
Explanation: ***Atracurium*** - **Sugammadex** is a modified gamma-cyclodextrin that specifically encapsulates and inactivates **aminosteroid neuromuscular blocking agents**. - **Atracurium** is a **benzylisoquinolinium** agent, not an aminosteroid, therefore it cannot be reversed by sugammadex. *Vecuronium* - **Vecuronium** is an **aminosteroid neuromuscular blocker**, which means it can be effectively encapsulated and reversed by **sugammadex**. - Its chemical structure allows for a high affinity binding with sugammadex, leading to rapid reversal of neuromuscular blockade. *Pancuronium* - **Pancuronium** is an **aminosteroid neuromuscular blocker** that can be effectively reversed by **sugammadex**. - Although sugammadex has a lower affinity for pancuronium compared to rocuronium, it can still effectively reverse its blockade. *Rocuronium* - **Rocuronium** is an **aminosteroid neuromuscular blocker** with the **highest affinity for sugammadex**, making it the most rapidly and effectively reversed by this agent. - The strong, non-covalent binding between sugammadex and rocuronium forms a stable complex, preventing rocuronium from interacting with acetylcholine receptors.
Question 6: Which drug can exhibit Phase II neuromuscular block:
- A. Scoline (Correct Answer)
- B. Cocaine
- C. D-TC
- D. Vencuronium, ether, N2O
Explanation: ***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.
Question 7: Mechanism of action of curare-like drugs?
- A. Blocks ACh receptors (Correct Answer)
- B. Agonistic with ACh receptors
- C. Inhibits ACh synthesis
- D. Causes persistent depolarization
Explanation: ***Blocks ACh receptors*** - Curare-like drugs are **competitive antagonists** at the **nicotinic acetylcholine receptors (nAChRs)** found at the neuromuscular junction. - By binding to these receptors, they prevent acetylcholine (ACh) from binding and activating the receptors, thereby **inhibiting muscle contraction**. *Inhibits ACh synthesis* - Drugs that inhibit ACh synthesis typically target enzymes like **choline acetyltransferase**. - This mechanism would reduce the amount of ACh available, but curare acts directly at the *receptor level*. *Causes persistent depolarization* - This is the mechanism of action of **depolarizing neuromuscular blockers** like succinylcholine. - They initially activate the receptor, causing a brief depolarization, followed by a sustained depolarization that renders the muscle unresponsive. *Agonistic with ACh receptors* - An agonist binds to and activates a receptor, mimicking the effect of the natural ligand (acetylcholine in this case). - Curare-like drugs are **antagonists**; they bind to the receptor but do not activate it, instead blocking ACh binding.
Question 8: Hippus occurs in which poisoning?
- A. Aconite poisoning (Correct Answer)
- B. Opioid poisoning
- C. Neuromuscular blocking agent poisoning
- D. Belladonna poisoning
Explanation: ***Aconite poisoning*** - **Hippus**, characterized by alternating **pupillary constriction and dilation**, is a hallmark of aconite poisoning. - This unusual pupil activity results from the **neurotoxic effects** of aconite on the autonomic nervous system. *Opioid poisoning* - Opioid poisoning typically causes characteristic **pinpoint pupils (miosis)** due to parasympathetic overstimulation. - Hippus is not a feature of opioid toxicity. *Neuromuscular blocking agent poisoning* - Neuromuscular blocking agents primarily affect the **skeletal muscles**, leading to **paralysis** but generally do not directly impact pupil size or reactivity. - Pupils usually remain **mid-dilated and fixed** in severe paralysis, but not hippus. *Belladonna poisoning* - Belladonna (atropine) poisoning causes **mydriasis (dilated pupils)** due to its anticholinergic effect, blocking parasympathetic activity. - The pupils are typically fixed and dilated, not exhibiting hippus.
Question 9: Which of the following is not a recognized use of alpha-2-agonists?
- A. Glaucoma
- B. Hypertension
- C. Sedation
- D. Benign Hyperplasia of prostate (Correct Answer)
Explanation: ***Correct Answer: Benign Hyperplasia of prostate*** - Alpha-2-agonists are **NOT** used to treat **benign prostatic hyperplasia (BPH)**; this condition is typically managed with **alpha-1-blockers** (e.g., tamsulosin, alfuzosin) or 5-alpha-reductase inhibitors. - Alpha-1-blockers relax the smooth muscle in the prostate and bladder neck, improving urine flow, which involves a different receptor mechanism than alpha-2-agonists. - Alpha-2-agonists would not provide therapeutic benefit for BPH. *Incorrect: Glaucoma* - Alpha-2-agonists (e.g., **brimonidine**, **apraclonidine**) **are** used to treat **glaucoma** by reducing aqueous humor production and increasing uveoscleral outflow. - This action helps to **lower intraocular pressure**, a primary goal in glaucoma management. *Incorrect: Hypertension* - Central-acting alpha-2-agonists (e.g., **clonidine**, **methyldopa**) **are** used as **antihypertensive agents**. - They reduce sympathetic outflow from the central nervous system, leading to decreased heart rate, vasodilation, and consequently, **lower blood pressure**. *Incorrect: Sedation* - Alpha-2-agonists like **dexmedetomidine** and **clonidine** **are** commonly used for **sedation** in critically ill patients, especially in intensive care units. - They produce sedation, analgesia, and anxiolysis without causing significant respiratory depression, making them valuable in certain clinical settings.
Question 10: Which sympathomimetic drug is primarily known to increase heart rate?
- A. Isoprenaline (Correct Answer)
- B. Phenylephrine
- C. Noradrenaline
- D. Adrenaline
Explanation: ***Isoprenaline*** - **Isoprenaline** (isoproterenol) is a non-selective beta-adrenergic agonist, with a strong affinity for **β1 and β2 receptors** [1]. - Its activation of **β1 receptors** in the heart leads to a significant increase in **heart rate (positive chronotropy)** and contractility (positive inotropy) [1]. - It is the **most potent chronotropic agent** among sympathomimetics and is primarily known for increasing heart rate [2]. *Phenylephrine* - **Phenylephrine** is a selective **α1 adrenergic agonist** that causes vasoconstriction [4]. - It increases blood pressure but typically causes **reflex bradycardia** (decreased heart rate) due to baroreceptor activation. - Does NOT directly increase heart rate. *Noradrenaline* - **Noradrenaline** (norepinephrine) primarily acts on **α1 receptors** causing vasoconstriction, and to a lesser extent on **β1 receptors** [3]. - While it can stimulate β1 receptors, its predominant effect is to increase **mean arterial pressure** through vasoconstriction, often causing **reflex bradycardia** [3]. *Adrenaline* - **Adrenaline** (epinephrine) acts on **α1, β1, and β2 receptors** [4]. While it does increase heart rate via **β1 receptor** stimulation, it also causes significant **vasoconstriction** (via α1) and **vasodilation** (via β2). - Its cardiovascular effects are more complex and dose-dependent compared to isoprenaline's specific chronotropic action.
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