Autonomic Nervous System Drugs Practice Questions

Q: Which sympathomimetic drug acts on D1, D2, and beta-1 receptors, but not on beta-2 receptors?

Dopamine. ### Explanation **Correct Answer: C. Dopamine** **Mechanism and Concept:** Dopamine is a unique catecholamine that exhibits **dose-dependent receptor selectivity**. At different infusion rates, it acts on specific receptors: 1. **Low dose ( 10 µg/kg/min):** Acts on **Alpha-1 ($\alpha_1$)** receptors (causing vasoconstriction). Crucially, Dopamine has **no significant action on Beta-2 ($\beta_2$)** receptors, which distinguishes it from other inotropes like dobutamine or dopexamine. **Why other options are incorrect:** * **Dobutamine:** Primarily a $\beta_1$ agonist with some $\beta_2$ and $\alpha_1$ activity. It lacks dopaminergic (D1/D2) activity. * **Dopexamine:** A synthetic analog that acts on **D1, D2, and $\beta_2$** receptors. It lacks significant $\beta_1$ and $\alpha_1$ activity. * **Isoprenaline:** A pure, non-selective Beta agonist ($\beta_1 + \beta_2$). It has no effect on Alpha or Dopamine receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Fenoldopam:** A selective **D1 agonist** used in hypertensive emergencies to maintain renal perfusion. * **Drug of Choice:** Dopamine was historically used for cardiogenic shock with oliguria, though Norepinephrine is now preferred in many protocols. * **Renal Dose Myth:** While low-dose dopamine increases renal blood flow via D1 receptors, clinical trials (like the SOAP II trial) have shown it does not prevent acute renal failure. * **Adverse Effect:** Can cause tachycardia and arrhythmias due to $\beta_1$ stimulation.

Q: All of the following are seen in atropine poisoning EXCEPT?

Hypothermia. **Explanation:** Atropine is a competitive antagonist of muscarinic acetylcholine receptors. The correct answer is **Hypothermia** because atropine poisoning actually causes **Hyperthermia** [1]. **1. Why Hypothermia is the Correct Answer (The Exception):** Atropine blocks $M_3$ receptors on sweat glands, leading to **anhidrosis** (suppression of sweating). Since sweating is the body's primary mechanism for heat dissipation, blockade results in a rise in body temperature [1]. This is especially dangerous in children and is often referred to as "Atropine fever." **2. Analysis of Incorrect Options:** * **Mydriasis (Option A):** Atropine blocks $M_3$ receptors on the pupillary sphincter muscle, leading to passive mydriasis (dilated pupils) and cycloplegia (loss of accommodation). * **Hallucination (Option B):** Atropine is a tertiary amine that crosses the blood-brain barrier. Toxic doses cause central anticholinergic effects, including restlessness, disorientation, and vivid visual hallucinations. * **Coma (Option C):** In severe poisoning, the initial central nervous system stimulation is followed by depression, leading to circulatory collapse, respiratory failure, and coma. **Clinical Pearls for NEET-PG:** To remember the clinical features of atropine poisoning, use the classic mnemonic: * **Red as a beet:** Cutaneous vasodilation (Atropine flush). * **Dry as a bone:** Anhidrosis and dry mouth [1]. * **Hot as a hare:** Hyperthermia [1]. * **Blind as a bat:** Mydriasis and cycloplegia. * **Mad as a hatter:** Delirium and hallucinations. * **Full as a flask:** Urinary retention [1]. **High-Yield Fact:** The specific antidote for atropine poisoning is **Physostigmine** (a tertiary carbamate) because it crosses the blood-brain barrier to reverse both peripheral and central symptoms.

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: Which one of the following is NOT an ergot alkaloid?

Ketanserin. **Explanation:** The correct answer is **Ketanserin (Option C)**. **Why Ketanserin is the correct answer:** Ketanserin is a selective **5-HT₂ receptor antagonist** with additional $\alpha_1$-blocking properties. Unlike the other options, it is a synthetic quinazoline derivative, not an ergot alkaloid. It is primarily used clinically as an antihypertensive agent (though rarely now) and to treat vasospastic conditions like Raynaud’s phenomenon. **Analysis of Incorrect Options:** * **Bromocriptine (Option A):** A semisynthetic ergot alkaloid that acts as a potent **D2 receptor agonist**. It is high-yield for its use in Hyperprolactinemia, Acromegaly, and Parkinson’s disease. * **Lysergic acid diethylamide (LSD) (Option B):** A potent semisynthetic ergot derivative known for its hallucinogenic properties. It acts primarily as an agonist at 5-HT$_{2A}$ receptors in the CNS. * **Methysergide (Option D):** A semisynthetic ergot alkaloid used historically for migraine prophylaxis. It is a 5-HT$_{2A/2C}$ antagonist. **High-Yield Clinical Pearls for NEET-PG:** 1. **Ergot Alkaloids Source:** Derived from the fungus *Claviceps purpurea*. 2. **The "Ergot" Side Effect:** Methysergide is notorious for causing **retroperitoneal, pleural, and endocardial fibrosis** with prolonged use. 3. **Specific Ergot Uses:** * **Ergotamine:** Acute migraine attack (vasoconstrictor). * **Ergonovine (Ergometrine):** Postpartum hemorrhage (PPH) due to its strong oxytocic effect (contraindicated in pregnancy before delivery). 4. **Ergotism (St. Anthony’s Fire):** Poisoning characterized by severe peripheral vasoconstriction leading to gangrene and CNS hallucinations.

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.

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 sympathomimetic drug acts on D1, D2, and beta-1 receptors, but not on beta-2 receptors?

Accepted Answer

Dopamine

Answer

Dobutamine

Answer

Dopexamine

Answer

Isoprenaline

Question 3

All of the following are seen in atropine poisoning EXCEPT?

Accepted Answer

Hypothermia

Answer

Mydriasis

Answer

Hallucination

Answer

Coma

Question 4

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 5

Which one of the following is NOT an ergot alkaloid?

Accepted Answer

Ketanserin

Answer

Bromocriptine

Answer

Lysergic acid diethylamide (LSD)

Answer

Methysergide

Question 6

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

Accepted Answer

Phenylephrine

Answer

Histamine

Answer

Methoxamine

Answer

Dopamine

Question 7

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

Accepted Answer

Scopolamine

Answer

Dexmedetomidine

Answer

Atropine

Answer

Homatropine

Question 8

Neostigmine is used for reversing the adverse effect of which of the following?

Accepted Answer

Nondepolarizing neuromuscular blockers

Answer

Depolarizing neuromuscular blockers only

Answer

Alcuronium only

Answer

Ketamine complication

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

Diagnosis of Myasthenia gravis is typically done by using which of the following tests?

Accepted Answer

Edrophonium test

Answer

Neostigmine test

Answer

Succinylcholine administration

Answer

Atropine challenge

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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