Autonomic Nervous System Drugs Practice Questions

Q: Which muscle relaxant is primarily excreted by the kidneys?

Gallamine. Everything in nature is balanced. ***Gallamine*** - **Gallamine** is predominantly cleared from the body through **renal excretion** (>90%), with very low hepatic metabolism. - Due to its high reliance on kidney function for elimination, **gallamine** is contraindicated in patients with **renal impairment**. [2] - **Note**: Gallamine has limited current clinical use and has been withdrawn from many markets, but remains important for understanding muscle relaxant pharmacokinetics. *Pancuronium* - **Pancuronium** has significant renal elimination (~40-50%), along with hepatic metabolism and biliary excretion. - While renal excretion is clinically important for **pancuronium** (making dose adjustment necessary in renal impairment), gallamine has a higher percentage of renal excretion. - Among **currently used** muscle relaxants, pancuronium shows the greatest dependence on renal function. *Vecuronium* - **Vecuronium** is mainly eliminated by **hepatic metabolism** (60-80%) and **biliary excretion**, with only a small fraction (10-25%) excreted renally. [1] - Its intermediate duration of action is attributed to rapid redistribution and hepatic metabolism, making it relatively safer for patients with renal dysfunction. [1] *Atracurium* - **Atracurium** undergoes unique elimination via **Hofmann degradation** (non-enzymatic chemical breakdown at physiological pH and temperature) and **ester hydrolysis**, independent of organ function. [3] - This makes it the preferred choice in patients with **renal** or **hepatic failure** as its metabolism does not rely on these organs. [3]

Q: Side effects of Pilocarpine include:

Ciliary spasm. ***Ciliary spasm*** - **Pilocarpine** is a **direct-acting cholinergic agonist** that stimulates muscarinic receptors, leading to **ciliary muscle contraction**. - This contraction causes **accommodation spasm** (ciliary spasm), resulting in blurry vision, particularly at a distance. *Decreased lacrimation* - **Pilocarpine** actually **increases lacrimation** (tear production) due to its parasympathomimetic effects on the lacrimal glands. - Decreased lacrimation would be an anticholinergic effect, the opposite of pilocarpine's action. *Cycloplegia* - **Cycloplegia** refers to the **paralysis of the ciliary muscle**, leading to loss of accommodation, and is caused by **anticholinergic agents**. - **Pilocarpine**, as a cholinergic agonist, causes **ciliary muscle contraction**, which is the opposite of cycloplegia. *Mydriasis* - **Mydriasis** is the **dilation of the pupil** and is caused by **sympathomimetics** or **anticholinergics**. - **Pilocarpine** causes **miosis** (pupil constriction) through the contraction of the iris sphincter muscle.

Q: Beta blockers mask all effects of hypoglycemia except?

Sweating. ***Sweating*** - **Sweating** is a **cholinergic symptom** mediated by the sympathetic nervous system acting on **muscarinic receptors** (via acetylcholine), NOT beta-adrenergic receptors. - Beta-blockers act on **adrenergic receptors only** and therefore **do not mask sweating**. - This makes **sweating the most reliable clinical sign** of hypoglycemia in patients on beta-blocker therapy. - Sweating remains the classic teaching point for symptoms that persist despite beta-blockade. *Palpitations* - **Palpitations** are an **adrenergic symptom** resulting from increased heart rate and contractility, mediated by **beta-1 adrenergic receptors**. - Beta-blockers effectively **mask** this symptom by blocking these receptors, preventing the cardiovascular response to hypoglycemia. *Dizziness* - **Dizziness** is a **neuroglycopenic symptom** resulting from insufficient glucose supply to the brain. - While technically not masked by beta-blockers (as it's not mediated by beta receptors), dizziness represents a **late and dangerous sign** of severe hypoglycemia. - Sweating is the more reliable and **earlier warning sign** that remains detectable in beta-blocked patients. *Tremors* - **Tremors** are an **adrenergic symptom** caused by stimulation of **beta-2 adrenergic receptors** in skeletal muscle. - Beta-blockers, especially non-selective ones, effectively **mask this symptom** by blocking these receptors.

Q: Ocular effects that include mydriasis are characteristic of which of the following drugs?

phenylephrine (alpha agonist). ***phenylephrine (alpha agonist)*** - **Phenylephrine** is a direct-acting **alpha-1 adrenergic agonist** that causes contraction of the **pupillary dilator muscle**, leading to **mydriasis** (pupil dilation). [1] - It is frequently used clinically to dilate pupils for **ophthalmologic examinations** due to its selective action on alpha-1 receptors in the eye. [2] *neostigmine (cholinesterase inhibitor)* - **Neostigmine** inhibits acetylcholinesterase, increasing acetylcholine at the neuromuscular junction and muscarinic receptors. This leads to **miosis** (pupil constriction), not mydriasis. - Its ophthalmic use is primarily for treating **glaucoma** by improving aqueous humor outflow through cholinergic effects on the ciliary muscle. *phentolamine (alpha blocker)* - **Phentolamine** is a **non-selective alpha-adrenergic antagonist** that blocks both alpha-1 and alpha-2 receptors. - Alpha-1 receptor blockade in the eye would relax the pupillary dilator muscle, leading to **miosis** or prevention of mydriasis, not its induction. *mecamylamine (ganglionic blocker)* - **Mecamylamine** is a **ganglionic blocker** that antagonizes nicotinic receptors in both sympathetic and parasympathetic ganglia. - Blocking parasympathetic ganglia can cause some mydriasis, but ganglionic blockers have widespread, non-selective autonomic effects and are not primarily used for isolated mydriasis.

Q: Shortest-acting non-depolarizing muscle relaxant is:

Mivacurium. ***Mivacurium*** - **Mivacurium** is an intermediate-acting **non-depolarizing** neuromuscular blocker due to its rapid metabolism by **plasma cholinesterases**, making it the shortest-acting among the non-depolarizing agents available [1, 2]. - Its short duration of action (12-18 minutes) allows for quicker recovery of muscle function, which can be advantageous for **short surgical procedures** or for rapid control of muscle relaxation when precise timing is crucial [2]. *Succinylcholine* - **Succinylcholine** is a **depolarizing** neuromuscular blocker, not non-depolarizing, and has a very rapid onset and ultra-short duration of action (5-10 minutes) but acts through a different mechanism by mimicking acetylcholine. - Its use is associated with several side effects, including **malignant hyperthermia**, **hyperkalemia**, and **muscle pain**, which differ from those of non-depolarizing agents. *Atracurium* - **Atracurium** is an intermediate-acting non-depolarizing muscle relaxant that undergoes **Hofmann elimination** and **ester hydrolysis** for metabolism, giving it a duration of action of approximately 20-35 minutes, which is longer than mivacurium [1]. - While suitable for patients with renal or hepatic impairment due to its unique metabolism, it can cause **histamine release**, leading to hypotension or bronchospasm [2]. *Vecuronium* - **Vecuronium** is an intermediate-acting non-depolarizing muscle relaxant with a duration of action of about 25-40 minutes and is primarily eliminated by the liver and kidneys. - It is known for its **cardiovascular stability** as it does not cause histamine release or significant hemodynamic changes, but its longer duration makes it less ideal when very short-acting relaxation is needed.

Q: Which of the following is the shortest-acting competitive neuromuscular blocking agent?

Mivacurium. ***Mivacurium*** - Mivacurium is characterized by its **rapid onset** and **ultrashort duration** of action, primarily due to its hydrolysis by plasma pseudocholinesterase [3]. - This rapid metabolism makes it highly suitable for procedures requiring **brief neuromuscular blockade** or when rapid recovery is desirable. *Atracurium* - Atracurium has an **intermediate duration** of action and is primarily metabolized by **Hofmann elimination**, a non-enzymatic chemical degradation, and ester hydrolysis [3]. - While it's useful in patients with renal or hepatic dysfunction, its duration is significantly longer than mivacurium [4]. *Rocuronium* - Rocuronium is an **intermediate-acting** neuromuscular blocking agent known for its **rapid onset** of action, making it a common choice for **rapid sequence induction** [1]. - Its duration of action is longer than mivacurium and it is primarily eliminated by the kidneys and liver [2]. *Cisatracurium* - Cisatracurium is an **intermediate-acting** neuromuscular blocker that is an isomer of atracurium [3]. - It also undergoes **Hofmann elimination**, but it is more potent and produces fewer histamine release issues than atracurium, yet its duration is still longer than mivacurium [3].

Q: The α2 agonist used in glaucoma is:

Brimonidine. ***Correct: Brimonidine*** - **Brimonidine** is an **α2-adrenergic agonist** commonly used in the treatment of glaucoma - It works by reducing **aqueous humor production** and increasing **uveoscleral outflow**, thereby lowering intraocular pressure - Available as eye drops (0.1%, 0.15%, 0.2% concentrations) *Incorrect: Guanfacine* - **Guanfacine** is an **α2A-adrenergic agonist** primarily used to treat **attention deficit hyperactivity disorder (ADHD)** and **hypertension** - It does not have a primary role in glaucoma treatment *Incorrect: Guanabenz* - **Guanabenz** is an **α2-adrenergic agonist** that acts centrally to reduce **sympathetic outflow**, used mainly as an **antihypertensive agent** - It is not indicated for the treatment of glaucoma *Incorrect: Tizanidine* - **Tizanidine** is an **α2-adrenergic agonist** primarily used as a **muscle relaxant** to manage spasticity - It is not used for glaucoma

Q: Which of the following acts on the trabecular meshwork and increases aqueous outflow?

Pilocarpine. ***Pilocarpine*** - As a **muscarinic agonist**, pilocarpine contracts the **ciliary muscle**, which pulls on the scleral spur. - This action widens the spacing within the **trabecular meshwork**, increasing aqueous humor outflow. *Timolol* - Timolol is a **beta-blocker** that reduces the production of aqueous humor by the ciliary body. - It does not directly affect the structure or function of the trabecular meshwork to enhance outflow. *Brimonidine* - Brimonidine is an **alpha-2 adrenergic agonist** that reduces aqueous humor production and increases uveoscleral outflow. - It does not primarily act on the trabecular meshwork to facilitate outflow. *Brinzolamide* - Brinzolamide is a **carbonic anhydrase inhibitor** that decreases aqueous humor production by the ciliary body. - Its mechanism of action does not involve directly affecting the trabecular meshwork's outflow capacity.

Q: In an animal model, the phenomenon of vasomotor reversal of Dale can be demonstrated by which of the following?

Blocking alpha-1 followed by stimulation of beta-2. ***Blocking alpha-1 followed by stimulation of beta-2*** - **Dale's vasomotor reversal** occurs when the typical pressor response to epinephrine is converted to a depressor (vasodilator) response. This phenomenon is demonstrated by first blocking **alpha-1 adrenergic receptors** (e.g., with phenoxybenzamine or phentolamine), and then administering **epinephrine**. - With alpha-1 receptors blocked, epinephrine cannot cause vasoconstriction. Instead, its stimulation of **beta-2 receptors** is unmasked, leading to vasodilation and a drop in blood pressure—the opposite of the usual pressor response. - This is the classic demonstration of Dale's vasomotor reversal in animal models. *Stimulation of alpha-1 followed by stimulation of beta-2* - Simultaneous stimulation of **alpha-1** and **beta-2 receptors** (as occurs with endogenous epinephrine without any blockade) typically results in a net **vasoconstrictor effect** due to the dominance of alpha-1 signaling in most vascular beds. - This scenario represents the normal response to epinephrine, not a reversal phenomenon. *Stimulation of alpha-1 followed by block of beta-2* - Stimulating **alpha-1 receptors** while blocking **beta-2 receptors** would enhance **vasoconstriction**, as the vasodilatory effects of beta-2 activation would be removed. - This would intensify the normal pressor effect, which is opposite to Dale's reversal. *Stimulation of beta-1 receptor followed by block of beta-2 receptor* - Stimulation of **beta-1 receptors** primarily affects the heart (increasing heart rate and contractility), while blocking **beta-2 receptors** would remove peripheral vasodilation. - Neither action directly relates to the **vasomotor reversal phenomenon**, which specifically involves reversing the vascular response to adrenergic agonists from vasoconstriction to vasodilation.

Q: Action of dopamine at a dose of 1-2 mcg/kg/min is

Enhances renal blood flow. ***Enhances renal blood flow*** - At low doses (1-2 mcg/kg/min), dopamine primarily activates **dopamine D1 receptors** in the renal, mesenteric, and coronary vascular beds. - This activation leads to **vasodilation** in these areas, specifically increasing renal blood flow, glomerular filtration rate, and sodium excretion. *Causes vasoconstriction* - **Vasoconstriction** occurs at higher doses of dopamine (10 mcg/kg/min and above) due to stimulation of **alpha-1 adrenergic receptors**. - This effect is generally undesirable for renal perfusion and can lead to increased systemic vascular resistance. *Increases myocardial contractility* - **Increased myocardial contractility** is observed at moderate doses of dopamine (5-10 mcg/kg/min) due to stimulation of **beta-1 adrenergic receptors** in the heart. - This is a common indication for dopamine in cardiogenic shock but does not occur at the low 1-2 mcg/kg/min dose. *Elevates systemic blood pressure* - A significant **elevation in systemic blood pressure** is primarily seen at higher doses of dopamine (greater than 10 mcg/kg/min) due to the combined effects of **vasoconstriction (alpha-1 stimulation)** and increased cardiac output (beta-1 stimulation). - At 1-2 mcg/kg/min, the vasodilatory effects in some vascular beds might even cause a slight decrease or no significant change in systemic blood pressure unless other factors are at play.

Question 1

Which muscle relaxant is primarily excreted by the kidneys?

Accepted Answer

Gallamine

Answer

Vecuronium

Answer

Pancuronium

Answer

Atracurium

Question 2

Side effects of Pilocarpine include:

Accepted Answer

Ciliary spasm

Answer

Cycloplegia

Answer

Decreased lacrimation

Answer

Mydriasis

Question 3

Beta blockers mask all effects of hypoglycemia except?

Accepted Answer

Sweating

Answer

Palpitations

Answer

Dizziness

Answer

Tremors

Question 4

Ocular effects that include mydriasis are characteristic of which of the following drugs?

Accepted Answer

phenylephrine (alpha agonist)

Answer

neostigmine (cholinesterase inhibitor)

Answer

phentolamine (alpha blocker)

Answer

mecamylamine (ganglionic blocker)

Question 5

Shortest-acting non-depolarizing muscle relaxant is:

Accepted Answer

Mivacurium

Answer

Atracurium

Answer

Succinylcholine

Answer

Vecuronium

Question 6

Which of the following is the shortest-acting competitive neuromuscular blocking agent?

Accepted Answer

Mivacurium

Answer

Atracurium

Answer

Rocuronium

Answer

Cisatracurium

Question 7

The α2 agonist used in glaucoma is:

Accepted Answer

Brimonidine

Answer

Guanabenz

Answer

Guanfacine

Answer

Tizanidine

Question 8

Which of the following acts on the trabecular meshwork and increases aqueous outflow?

Accepted Answer

Pilocarpine

Answer

Timolol

Answer

Brimonidine

Answer

Brinzolamide

Question 9

In an animal model, the phenomenon of vasomotor reversal of Dale can be demonstrated by which of the following?

Accepted Answer

Blocking alpha-1 followed by stimulation of beta-2

Answer

Stimulation of alpha-1 followed by stimulation of beta-2

Answer

Stimulation of alpha-1 followed by block of beta-2

Answer

Stimulation of beta-1 receptor followed by block of beta-2 receptor

Question 10

Action of dopamine at a dose of 1-2 mcg/kg/min is

Accepted Answer

Enhances renal blood flow

Answer

Causes vasoconstriction

Answer

Increases myocardial contractility

Answer

Elevates systemic blood pressure

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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