Autonomic Nervous System Drugs Practice Questions

Q: Which of the following is a contraindication for the use of beta blockers?

Asthma. ***Asthma*** - Beta-blockers can cause **bronchoconstriction** by blocking beta-2 adrenergic receptors in the lungs, worsening asthma symptoms. - This effect can precipitate or exacerbate an **asthma attack**, making it a significant contraindication, especially for non-selective beta-blockers. *Myocardial infarction* - Beta-blockers are often **indicated** in the post-myocardial infarction setting to reduce myocardial oxygen demand, heart rate, and risk of future events. - They improve survival by preventing remodeling and reducing the incidence of **ventricular arrhythmias**. *Hypertension* - Beta-blockers are a common and effective treatment for **hypertension**, lowering blood pressure by reducing heart rate and cardiac output. - They are particularly useful when hypertension is accompanied by **angina** or **migraines**. *Arrhythmia* - Beta-blockers are frequently used to treat various **arrhythmias**, such as **atrial fibrillation** and **supraventricular tachycardia**. - They decrease the heart rate and conduction velocity through the AV node, helping to **control ventricular response**.

Q: Mirabegron is a:

Beta-3 adrenergic agonist. Mirabegron is a: ***Beta-3 adrenergic agonist*** - **Mirabegron** selectively stimulates **beta-3 adrenergic receptors** in the bladder [1]. - This activation leads to **relaxation of the detrusor muscle**, increasing bladder capacity and reducing urgency. *Beta-3 antagonist* - An **antagonist** would block the beta-3 receptors, which would constrict the detrusor muscle and worsen symptoms of overactive bladder. - This mechanism of action is opposite to the therapeutic effect of mirabegron. *Beta-1 agonist* - **Beta-1 agonists** primarily affect the heart, increasing heart rate and contractility. - Mirabegron has very low affinity for beta-1 receptors, making this an incorrect classification. *Beta-1 antagonist* - **Beta-1 antagonists** (beta-blockers) are used to decrease heart rate and blood pressure. - This is an entirely different pharmacological class with no direct relevance to mirabegron's mechanism of action on the bladder.

Q: Which of the following is a depolarizing muscle relaxant?

Succinylcholine. ***Succinylcholine*** - **Succinylcholine** is the only **depolarizing neuromuscular blocker** used clinically [1], [2]. - It works by acting as an **acetylcholine receptor agonist**, causing initial muscle fasciculations followed by sustained depolarization and paralysis [3], [4]. - Characterized by Phase I block (not reversed by anticholinesterases) [4]. *Vecuronium* - **Vecuronium** is a **non-depolarizing neuromuscular blocker** (competitive antagonist). - It acts by competitively blocking acetylcholine at the neuromuscular junction without causing depolarization. - Can be reversed by anticholinesterases like neostigmine. *Rocuronium* - **Rocuronium** is a **non-depolarizing muscle relaxant** with rapid onset of action [1]. - It competitively blocks nicotinic receptors at the neuromuscular junction. - Can be reversed by sugammadex (specific reversal agent) or anticholinesterases. *Atracurium* - **Atracurium** is a **non-depolarizing neuromuscular blocker** with intermediate duration. - Undergoes Hofmann elimination and ester hydrolysis, making it useful in renal/hepatic failure. - Does not cause depolarization; acts as a competitive antagonist at the nicotinic receptor.

Q: All are true regarding prazosin, except which of the following?

Impaired glucose tolerance. ***Impaired glucose tolerance*** - Prazosin, an **alpha-1-adrenergic blocker**, does not typically cause impaired glucose tolerance [1]. - Unlike **beta-blockers**, alpha-blockers generally have a neutral or even slightly beneficial effect on glucose metabolism [1]. *First dose effect* - This is a well-known side effect of prazosin, characterized by **marked hypotension** and **syncope** after the initial dose. - It occurs due to sudden **peripheral vasodilation** following alpha-1 blockade [1]. *Selective alpha-1 blocker* - Prazosin specifically and selectively blocks **alpha-1 adrenergic receptors**, leading to arterial and venous dilation [1]. - This selectivity differentiates it from non-selective alpha-blockers. *Is an antihypertensive drug* - Prazosin is indeed used as an **antihypertensive drug** due to its ability to reduce peripheral vascular resistance by blocking alpha-1 receptors on blood vessels [1]. - This action leads to a decrease in **blood pressure** [1].

Q: Which of the following drugs is known to cross the blood-brain barrier?

Physostigmine. ***Physostigmine*** - **Physostigmine** is a **tertiary amine** that is uncharged at physiological pH, allowing it to readily cross the **lipophilic blood-brain barrier**. - Its ability to enter the central nervous system makes it useful for treating **central anticholinergic toxicity**, as it can inhibit acetylcholinesterase in the brain. *Glycopyrrolate* - **Glycopyrrolate** is a **quaternary ammonium compound**, meaning it carries a permanent positive charge. - This charge prevents it from crossing the **blood-brain barrier** effectively, limiting its effects to the peripheral nervous system. *Neostigmine* - **Neostigmine** is also a **quaternary ammonium compound**, similar to glycopyrrolate, making it highly ionized. - Due to its poor lipid solubility and charge, **neostigmine** has very limited penetration into the **central nervous system**. *All of the options* - This option is incorrect because both **glycopyrrolate** and **neostigmine** are charged molecules that do not readily cross the **blood-brain barrier**. - Only **physostigmine** among the listed drugs possesses the necessary lipophilicity to enter the central nervous system.

Q: Which of the following effects of adrenaline would be blocked by phentolamine but not by propranolol?

Contraction of radial smooth muscle in the iris. ***Contraction of radial smooth muscle in the iris*** - This effect is mediated by **α1-adrenergic receptors**. **Phentolamine** is a non-selective **α-blocker** and would block this effect. - **Propranolol** is a **non-selective β-blocker** and would not block α1-mediated effects. *Cardiac stimulation* - This effect is primarily mediated by **β1-adrenergic receptors** in the heart. - **Propranolol** is a non-selective **β-blocker** and would block this effect, while phentolamine (an **α-blocker**) would not. *Relaxation of bronchial smooth muscle* - This effect is mediated by **β2-adrenergic receptors** in the bronchi. - **Propranolol**, a non-selective **β-blocker**, would block this effect, potentially causing bronchoconstriction in susceptible individuals. Phentolamine would not. *Relaxation of uterus* - This effect is mediated by **β2-adrenergic receptors** in the uterus. - **Propranolol** would block this β2-mediated relaxation, while **phentolamine** (an α-blocker) would not.

Q: Cholinomimetic is not used for:

Bradycardia. ***Bradycardia*** - **Cholinomimetics** generally cause **bradycardia** (slowing of heart rate) due to their parasympathomimetic effects. Therefore, they are contraindicated in cases of existing bradycardia. - Using them in a patient with bradycardia would further decrease heart rate, potentially leading to adverse cardiovascular events. *Open angle glaucoma* - **Cholinomimetics** (e.g., pilocarpine) are used in open-angle glaucoma to cause **miosis** (pupil constriction) and **ciliary muscle contraction**. - This action increases the outflow of **aqueous humor** through the trabecular meshwork, thus reducing intraocular pressure. *Cobra bite* - **Neurotoxic snake venoms**, such as from a cobra, contain toxins that block acetylcholine receptors at the **neuromuscular junction**. - **Cholinomimetics** (specifically acetylcholinesterase inhibitors like neostigmine) can be used as an adjunct treatment to overcome this block by increasing the concentration of acetylcholine in the synaptic cleft. *Myasthenia gravis* - **Myasthenia gravis** is an autoimmune disease where antibodies block or destroy **nicotinic acetylcholine receptors** at the neuromuscular junction, leading to muscle weakness. - **Cholinomimetics** (specifically acetylcholinesterase inhibitors like pyridostigmine) are a cornerstone of treatment as they increase the amount of acetylcholine available to bind to the remaining functional receptors, improving muscle strength.

Q: Which substance reduces the regional arterial resistance of the mesentery and kidney vessels?

A) Dopamine. **Dopamine** - **Low doses of dopamine** activate **D1 receptors** in the renal and mesenteric vascular beds, leading to **vasodilation** and increased blood flow. - This specific action makes dopamine useful in situations where improved renal and mesenteric perfusion is desired, such as in certain types of **shock** [1]. *Dobutamine* - Primarily acts as a **beta-1 adrenergic agonist**, increasing myocardial contractility and heart rate. - It has **minimal effect** on mesenteric or renal vascular resistance at therapeutic doses. *Noradrenaline* - Also known as **norepinephrine**, it is a potent **alpha-1 adrenergic agonist** that causes **vasoconstriction** in most vascular beds, including the mesenteric and renal arteries [1]. - This action would increase, not decrease, regional arterial resistance. *Isoprenaline* - Primarily a **non-selective beta-adrenergic agonist** with significant **beta-1** and **beta-2** effects. - While it causes vasodilation in some vascular beds (due to beta-2 activation), it does not specifically target and reduce resistance in the mesenteric and renal vessels in the same way as low-dose dopamine.

Q: A patient on atracurium develops seizures due to accumulation of which substance?

Laudanosine. ***Laudanosine*** - Atracurium is metabolized into **laudanosine**, a **neurotoxic metabolite** that can accumulate, particularly in patients with renal or hepatic dysfunction, leading to **seizures** and central nervous system excitation. - Due to its potential for neurotoxicity, atracurium is often replaced by **cisatracurium**, which produces less laudanosine. *Cisatracurium* - **Cisatracurium** is an isomer of atracurium that is also metabolized via **Hofmann elimination** but produces significantly **less laudanosine**. - It is preferred in patients with **renal or hepatic impairment** due to its reduced potential for metabolite accumulation and neurotoxicity. *Atracurium acid* - Atracurium acid is one of the **inactive metabolites** of atracurium, along with laudanosine. - Unlike laudanosine, atracurium acid is **not neurotoxic** and does not contribute to seizure activity. *Histamine* - Atracurium can cause an **immediate release of histamine**, leading to transient hypotension, flushing, and bronchospasm, especially with rapid bolus injection. - While histamine release is an adverse effect of atracurium, it is **not directly responsible for seizure activity**.

Q: Which beta blocker is considered safer for use in patients with hepatic disease?

Esmolol. **Correct: Esmolol** - **Esmolol** is primarily metabolized by **plasma esterases** (red blood cell esterases), not the liver, making it the safest beta-blocker for patients with **hepatic impairment**. - Its **ultra-short half-life** (approximately 9 minutes) and rapid extrahepatic metabolism minimize drug accumulation and adverse effects in liver disease. - Commonly used in acute settings (ICU, perioperative) where rapid titration is needed. *Incorrect: Betaxolol* - **Betaxolol** is primarily metabolized by the **liver**, and its half-life can be significantly prolonged in patients with hepatic dysfunction. - This increased half-life can lead to **drug accumulation** and an elevated risk of adverse effects such as bradycardia and hypotension. *Incorrect: Bisoprolol* - **Bisoprolol** is eliminated by both **hepatic metabolism** (50%) and **renal excretion** (50%); however, significant liver impairment can still affect its clearance. - While it has a dual elimination pathway providing some safety margin, dose adjustments are often required in severe hepatic dysfunction. *Incorrect: Carvedilol* - **Carvedilol** is extensively metabolized by the **liver**, primarily through CYP2D6 and CYP2C9, leading to significantly altered pharmacokinetics in hepatic disease. - It should be **used with caution in hepatic impairment** due to substantial increase in bioavailability (up to 4-fold) and risk of adverse events including severe hypotension.

Question 1

Which of the following is a contraindication for the use of beta blockers?

Accepted Answer

Asthma

Answer

Myocardial infarction

Answer

Arrhythmia

Answer

Hypertension

Question 2

Mirabegron is a:

Accepted Answer

Beta-3 adrenergic agonist

Answer

Beta-3 antagonist

Answer

Beta-1 agonist

Answer

Beta-1 antagonist

Question 3

Which of the following is a depolarizing muscle relaxant?

Accepted Answer

Succinylcholine

Answer

Rocuronium

Answer

Vecuronium

Answer

Atracurium

Question 4

All are true regarding prazosin, except which of the following?

Accepted Answer

Impaired glucose tolerance

Answer

Selective alpha-1 blocker

Answer

Is an antihypertensive drug

Answer

First dose effect

Question 5

Which of the following drugs is known to cross the blood-brain barrier?

Accepted Answer

Physostigmine

Answer

Glycopyrrolate

Answer

Neostigmine

Answer

All of the options

Question 6

Which of the following effects of adrenaline would be blocked by phentolamine but not by propranolol?

Accepted Answer

Contraction of radial smooth muscle in the iris

Answer

Cardiac stimulation

Answer

Relaxation of bronchial smooth muscle

Answer

Relaxation of uterus

Question 7

Cholinomimetic is not used for:

Accepted Answer

Bradycardia

Answer

Cobra bite

Answer

Myasthenia gravis

Answer

Open angle glaucoma

Question 8

Which substance reduces the regional arterial resistance of the mesentery and kidney vessels?

Accepted Answer

A) Dopamine

Answer

B) Dobutamine

Answer

D) Isoprenaline

Answer

C) Noradrenaline

Question 9

A patient on atracurium develops seizures due to accumulation of which substance?

Accepted Answer

Laudanosine

Answer

Atracurium acid

Answer

Cisatracurium

Answer

Histamine

Question 10

Which beta blocker is considered safer for use in patients with hepatic disease?

Accepted Answer

Esmolol

Answer

Betaxolol

Answer

Bisoprolol

Answer

Carvedilol

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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