Autonomic Nervous System Drugs Practice Questions

Q: Which of the following statements is incorrect regarding prazosin?

It is an alpha-2 presynaptic blocker.. **Explanation:** Prazosin is a prototype **selective alpha-1 (α₁)** adrenergic receptor antagonist. Understanding its selectivity is crucial for NEET-PG pharmacology. **1. Why Option A is Incorrect (The Correct Answer):** Prazosin is highly selective for **postsynaptic α₁ receptors** and has negligible affinity for α₂ receptors. By sparing the presynaptic α₂ receptors, it does not interfere with the negative feedback loop of norepinephrine release. In contrast, non-selective blockers like Phenoxybenzamine block α₂ receptors, leading to increased norepinephrine release and significant reflex tachycardia—a side effect that is much less prominent with Prazosin. **2. Analysis of Other Options:** * **Option B (Orally effective):** Prazosin is well-absorbed from the gastrointestinal tract and is administered orally, typically 2–3 times daily due to its relatively short half-life. * **Option C (Metabolized in the liver):** It undergoes extensive hepatic metabolism (primarily via demethylation and conjugation). Dosage adjustment may be necessary in patients with severe liver dysfunction. * **Option D (First-dose effect):** This is a classic side effect of Prazosin. Patients may experience sudden, severe orthostatic hypotension and syncope shortly after the initial dose. To mitigate this, the "start low, go slow" approach is used, often administering the first dose at bedtime. **High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Hypertension, Raynaud’s phenomenon, and Benign Prostatic Hyperplasia (BPH) (though tamsulosin is more uro-selective). * **Specific Use:** It is the drug of choice for treating **scorpion sting** (Mesobuthus tamulus) induced hypertension and pulmonary edema. * **Comparison:** Unlike non-selective blockers, Prazosin improves the lipid profile by decreasing LDL and triglycerides while increasing HDL.

Q: All of the following beta blockers have intrinsic sympathomimetic activity EXCEPT:

Propranolol. **Explanation:** The question tests the knowledge of **Intrinsic Sympathomimetic Activity (ISA)**, also known as partial agonist activity. Beta-blockers with ISA do not cause a complete blockade of beta-receptors; instead, they stimulate them weakly while preventing the binding of more potent endogenous catecholamines. **1. Why Propranolol is the correct answer:** Propranolol is a **pure beta-antagonist** (non-selective). It lacks ISA, meaning it provides a complete blockade of $\beta_1$ and $\beta_2$ receptors. This results in a more significant reduction in resting heart rate and cardiac output compared to drugs with ISA. Because it lacks ISA, it is more likely to cause profound bradycardia and is the gold standard for conditions requiring strict heart rate control. **2. Analysis of incorrect options (Drugs WITH ISA):** * **Pindolol:** A non-selective beta-blocker with the highest degree of ISA. It is the classic example used in exams. * **Acebutolol:** A cardioselective ($\beta_1$) blocker that possesses significant ISA. * **Celiprolol:** A unique third-generation cardioselective blocker that has ISA at $\beta_2$ receptors (causing bronchodilation) and antagonist activity at $\beta_1$ receptors. **3. High-Yield Clinical Pearls for NEET-PG:** * **Benefit of ISA:** These drugs cause less resting bradycardia and less coldness of extremities (Raynaud's-like symptoms) because they maintain a basal level of receptor stimulation. * **Contraindication:** Drugs with ISA are generally **avoided** in the immediate post-MI period and in patients with severe angina because they do not reduce the myocardial oxygen demand as effectively as pure antagonists like Propranolol or Atenolol. * **Mnemonic for ISA:** "**P**apa **A**nd **C**hild **L**ove **O**ats" (**P**indolol, **A**cebutolol, **C**eliprolol, **L**abetalol, **O**xprenolol).

Q: Which of the following drugs is used for nasal decongestion both orally and topically?

Phenylephrine. **Explanation:** **Phenylephrine** is a potent, selective **$\alpha_1$-adrenergic agonist**. Its primary mechanism for nasal decongestion involves the stimulation of $\alpha_1$ receptors on the vascular smooth muscle of the nasal mucosa. This leads to **vasoconstriction**, which reduces edema, decreases mucus secretion, and shrinks swollen turbinates, thereby opening the airway. Phenylephrine is unique among common decongestants because it is effective through two routes: * **Topical:** Administered as nasal drops or sprays for rapid, localized action. * **Oral:** Found in many over-the-counter "cold and flu" formulations (though it has low systemic bioavailability due to first-pass metabolism). **Analysis of Incorrect Options:** * **Histamine (B):** Histamine is a mediator of inflammation and allergy. It causes vasodilation and increased capillary permeability, which actually **worsens** nasal congestion and rhinorrhea. * **Methoxamine (C):** While it is a selective $\alpha_1$ agonist, it is primarily used parenterally to treat paroxysmal supraventricular tachycardia (PSVT) or hypotension during anesthesia. It is not used as a nasal decongestant. * **Dopamine (D):** This is a precursor to norepinephrine that acts on D1, $\beta_1$, and $\alpha_1$ receptors (dose-dependent). It is used intravenously for hemodynamic support in shock, not for localized mucosal effects. **High-Yield NEET-PG Pearls:** * **Rhinitis Medicamentosa:** Prolonged use of topical decongestants (usually >3–5 days) like Phenylephrine or Oxymetazoline can lead to **rebound congestion** due to down-regulation of alpha receptors. * **Systemic Effects:** Even when used topically, Phenylephrine can cause systemic vasoconstriction; it should be used with caution in patients with **hypertension** or **BPH** (can cause urinary retention). * **Comparison:** **Pseudoephedrine** is another oral decongestant, but unlike Phenylephrine, it is not used topically.

Q: Which of the following drugs is available in the form of a transdermal patch?

Scopolamine. **Explanation:** **Scopolamine (Hyoscine)** is the correct answer because it is a highly lipid-soluble belladonna alkaloid that can be effectively absorbed through the skin. The **transdermal scopolamine patch** (applied behind the ear in the post-auricular area) is the gold standard for the prevention of **motion sickness**. It works by blocking muscarinic receptors in the vestibular apparatus and the vomiting center. The patch formulation provides a sustained release of the drug over 72 hours, minimizing the systemic side effects (like sedation and dry mouth) associated with oral administration. **Analysis of Incorrect Options:** * **Dexmedetomidine (Option A):** This is a highly selective $\alpha_2$-adrenergic agonist used primarily for sedation in intensive care settings or procedural sedation. It is administered via **intravenous infusion**, not as a patch. * **Atropine (Option B):** While it is the prototype antimuscarinic, it is typically administered IV, IM, or as ophthalmic drops. It lacks the specific pharmacokinetic profile required for effective transdermal delivery in routine clinical practice. * **Homatropine (Option D):** This is a semi-synthetic derivative of atropine used almost exclusively as **mydriatic and cycloplegic eye drops**. It has a shorter duration of action than atropine but is not available as a patch. **High-Yield Clinical Pearls for NEET-PG:** * **Application Timing:** For motion sickness, the scopolamine patch should be applied **4 hours before** the journey begins. * **Other Transdermal Drugs in Pharmacology:** Remember the mnemonic **"FENTANYL"** or simply list: Fentanyl, Nitroglycerin, Nicotine, Testosterone, Estrogen, Clonidine, and Rivastigmine. * **Drug of Choice:** While Scopolamine is the DOC for *prophylaxis* of motion sickness, **Promethazine** or **Dimenhydrinate** are often used for treatment.

Q: Which of the following is a selective beta 2 agonist?

Pirbuterol. The question asks to identify a selective $\beta_2$ agonist. These agents primarily act on $\beta_2$ receptors located in the bronchial smooth muscle, uterus, and blood vessels, leading to bronchodilation and vasodilation. **Why Pirbuterol is correct:** **Pirbuterol** is a short-acting $\beta_2$-selective agonist (SABA). It is chemically related to albuterol and is used via inhalation for the relief of bronchospasm in conditions like asthma and COPD. Its selectivity for $\beta_2$ over $\beta_1$ receptors minimizes cardiac side effects like tachycardia. **Analysis of Incorrect Options:** * **A. Isoprenaline:** This is a **non-selective** $\beta$ agonist ($\beta_1 = \beta_2$). It stimulates both the heart ($\beta_1$) and relaxes bronchial smooth muscle ($\beta_2$), making it unsuitable for selective respiratory therapy. * **C. Dobutamine:** This is a relatively selective **$\beta_1$ agonist**. It is primarily used as an inotropic agent in acute heart failure and cardiogenic shock to increase cardiac output. * **D. Mirabegron:** This is a selective **$\beta_3$ agonist**. It is used clinically for the treatment of overactive bladder (OAB) by relaxing the detrusor muscle. **High-Yield Clinical Pearls for NEET-PG:** * **SABAs (Short-Acting):** Salbutamol (Albuterol), Terbutaline, Pirbuterol. (Drug of choice for acute asthma attacks). * **LABAs (Long-Acting):** Salmeterol, Formoterol. (Used for maintenance, never for acute relief). * **Ultra-LABAs:** Indacaterol, Vilanterol (once-daily dosing). * **Side Effects:** Muscle tremors (most common), palpitations, and hypokalemia (due to stimulation of Na+/K+ ATPase pump driving potassium into cells).

Q: Location of beta 3 receptors include:

Bladder. ### Explanation **Correct Answer: C. Bladder** **Underlying Medical Concept:** Beta-3 ($\beta_3$) adrenergic receptors are primarily located in **adipose tissue** and the **detrusor muscle** of the urinary bladder [1]. When stimulated by norepinephrine or selective agonists, $\beta_3$ receptors induce relaxation of the detrusor muscle. This increases the bladder's functional capacity and facilitates urine storage [1]. **Analysis of Options:** * **A. Bronchial muscle:** These are predominantly populated by **$\beta_2$ receptors**. Stimulation leads to bronchodilation (the basis for using Salbutamol in asthma). * **B. Vascular muscle:** Vascular smooth muscle contains **$\alpha_1$ receptors** (vasoconstriction) and **$\beta_2$ receptors** (vasodilation, especially in skeletal muscle vessels). $\beta_3$ receptors do not play a primary role here. * **C. Bladder (Correct):** The detrusor muscle contains $\beta_3$ receptors. Their activation promotes bladder filling [1]. * **D. Uterus:** The myometrium is dominated by **$\beta_2$ receptors**. Stimulation causes uterine relaxation (tocolysis), which is why $\beta_2$ agonists like Ritodrine or Isoxsuprine are used to delay premature labor. **Clinical Pearls for NEET-PG:** 1. **Mirabegron:** A selective $\beta_3$ agonist used clinically for the treatment of **Overactive Bladder (OAB)** and urge incontinence. It works by relaxing the detrusor during the storage phase. 2. **Lipolysis:** $\beta_3$ receptors in adipose tissue mediate thermogenesis and lipolysis (breakdown of fats). 3. **Mnemonic for Beta Receptors:** * $\beta_1$: **1 Heart** (Increases HR/Contractility) * $\beta_2$: **2 Lungs** (Bronchodilation + Uterine/Vascular relaxation) * $\beta_3$: **3 "B"s** (Bladder, Brown fat, Body fat)

Q: What is the treatment of hypertensive crisis in pheochromocytoma?

Phentolamine. **Explanation:** **1. Why Phentolamine is Correct:** Pheochromocytoma is a catecholamine-secreting tumor (epinephrine and norepinephrine) that causes severe hypertension via massive stimulation of **alpha-1 receptors**. **Phentolamine** is a potent, non-selective, competitive **alpha-adrenergic blocker**. It directly antagonizes the effects of circulating catecholamines on blood vessels, leading to rapid vasodilation and a decrease in blood pressure. It is the drug of choice for managing hypertensive crises during surgery or whenever catecholamine excess is suspected. **2. Why the Other Options are Incorrect:** * **Hydralazine:** While it is a direct vasodilator used in hypertensive emergencies (especially in pregnancy), it does not address the underlying catecholamine surge in pheochromocytoma and can cause reflex tachycardia. * **Guanethidine:** This is a post-ganglionic adrenergic neuron blocker. It is contraindicated because it initially causes a release of stored norepinephrine, which would dangerously worsen a pheochromocytoma crisis. * **Salmeterol:** This is a long-acting beta-2 agonist (LABA) used for asthma and COPD. It has no role in blood pressure management and could potentially worsen tachycardia. **3. NEET-PG High-Yield Pearls:** * **The "Alpha-First" Rule:** In pheochromocytoma, **always** give an alpha-blocker (e.g., Phenoxybenzamine for long-term, Phentolamine for crisis) *before* a beta-blocker. Giving a beta-blocker first leads to "unopposed alpha stimulation," causing a catastrophic rise in blood pressure. * **Phenoxybenzamine:** The preferred drug for preoperative management (irreversible alpha-blocker). * **Diagnosis:** Best initial screening test is urinary or plasma **metanephrines**.

Q: Which of the following is NOT true about succinylcholine (scoline)?

Is a non-depolarizing neuromuscular blocker. **Explanation:** Succinylcholine (Scoline) is the only **depolarizing neuromuscular blocker** used clinically. It works by mimicking acetylcholine at the nicotinic receptors of the motor endplate, causing persistent depolarization that prevents further muscle contraction. Therefore, Option C is incorrect (and the right answer) because it is not a non-depolarizing agent (like vecuronium or rocuronium). **Analysis of other options:** * **Option A (Fasciculations):** Before causing paralysis, succinylcholine causes disorganized muscle contractions known as fasciculations. This is a hallmark of depolarizing blocks. * **Option B (Increased Pressures):** Succinylcholine transiently increases **Intraocular Pressure (IOP)**, Intragastric Pressure, and Intracranial Pressure (ICP). This makes its use controversial in penetrating eye injuries or severe head trauma. * **Option D (Short-acting):** It has the fastest onset (30–60 seconds) and the shortest duration of action (5–10 minutes) among all relaxants, making it the drug of choice for **Rapid Sequence Induction (RSI)**. **High-Yield Clinical Pearls for NEET-PG:** 1. **Metabolism:** It is metabolized by **Pseudocholinesterase** (Plasma cholinesterase). Deficiency of this enzyme leads to prolonged apnea (Scoline Apnea). 2. **Hyperkalemia:** It can cause a rise in serum potassium (~0.5 mEq/L). It is strictly contraindicated in patients with burns, massive trauma, or upper motor neuron lesions due to the risk of fatal hyperkalemia. 3. **Malignant Hyperthermia:** Succinylcholine is a potent trigger for Malignant Hyperthermia (Treatment: Dantrolene). 4. **Side Effects:** Post-operative myalgia is a common complaint following its use.

Question 1

Acetylcholine is not used commercially because:

Accepted Answer

It is rapidly destroyed in the body.

Answer

It has a long duration of action.

Answer

It is costly to produce.

Answer

It crosses the blood-brain barrier.

Question 2

Which of the following statements is incorrect regarding prazosin?

Accepted Answer

It is an alpha-2 presynaptic blocker.

Answer

It is orally effective.

Answer

It is metabolized in the liver.

Answer

A first-dose effect may occur.

Question 3

All of the following beta blockers have intrinsic sympathomimetic activity EXCEPT:

Accepted Answer

Propranolol

Answer

Celiprolol

Answer

Pindolol

Answer

Acebutalol

Question 4

Which of the following drugs is used for nasal decongestion both orally and topically?

Accepted Answer

Phenylephrine

Answer

Histamine

Answer

Methoxamine

Answer

Dopamine

Question 5

Which of the following drugs is available in the form of a transdermal patch?

Accepted Answer

Scopolamine

Answer

Dexmedetomidine

Answer

Atropine

Answer

Homatropine

Question 6

Which of the following is a selective beta 2 agonist?

Accepted Answer

Pirbuterol

Answer

Isoprenaline

Answer

Dobutamine

Answer

Mirabegron

Question 7

Location of beta 3 receptors include:

Accepted Answer

Bladder

Answer

Bronchial muscle

Answer

Vascular muscle

Answer

Uterus

Question 8

What is the treatment of hypertensive crisis in pheochromocytoma?

Accepted Answer

Phentolamine

Answer

Hydralazine

Answer

Guanethidine

Answer

Salmeterol

Question 9

Several children at a summer camp were hospitalized with symptoms thought to be due to ingestion of food containing botulinum toxin. The effects of botulinum toxin are likely to include:

Accepted Answer

Cycloplegia

Answer

Bronchospasm

Answer

Diarrhea

Answer

Skeletal muscle spasms

Question 10

Which of the following is NOT true about succinylcholine (scoline)?

Accepted Answer

Is a non-depolarizing neuromuscular blocker

Answer

Causes fasciculations

Answer

Increases intraocular pressure (ICT)

Answer

Is a short-acting muscle relaxant

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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