Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs Indian Medical PG Practice Questions and MCQs

Question 51: What is the treatment of choice for a cheese reaction?

A. Prazocin
B. Pentazocine
C. Phentolamine (Correct Answer)
D. Phenoxybenzamine

Explanation: **Explanation:** The **Cheese Reaction** is a hypertensive crisis that occurs when individuals taking **MAO inhibitors** (specifically non-selective MAO-A inhibitors) consume foods rich in **Tyramine** (e.g., aged cheese, red wine, pickled fish). Tyramine is a sympathomimetic amine that normally undergoes oxidative deamination by MAO-A in the gut and liver. When MAO-A is inhibited, tyramine enters the systemic circulation and displaces massive amounts of norepinephrine from sympathetic nerve endings, leading to severe vasoconstriction and a dangerous rise in blood pressure. **Why Phentolamine is the Correct Choice:** Phentolamine is a **non-selective, short-acting alpha-blocker**. It is the drug of choice because it rapidly antagonizes the alpha-1 receptors responsible for tyramine-induced vasoconstriction, thereby lowering blood pressure quickly in an emergency setting. **Analysis of Incorrect Options:** * **Prazocin:** While it is an alpha-1 blocker, it is primarily used for chronic hypertension and BPH. It has a slower onset of action compared to intravenous phentolamine, making it less suitable for an acute hypertensive crisis. * **Pentazocine:** This is an opioid agonist-antagonist used for pain relief; it has no role in managing hypertensive emergencies. * **Phenoxybenzamine:** This is an **irreversible** non-selective alpha-blocker. Because its effects are long-lasting and difficult to reverse, it is used for the preoperative management of Pheochromocytoma rather than acute hypertensive episodes. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Pheochromocytoma (Pre-op):** Phenoxybenzamine. * **Drug of Choice for Pheochromocytoma (Intra-op crisis):** Phentolamine. * **Clonidine Withdrawal Hypertension:** Also treated with Phentolamine. * **MAO-B Inhibitors (e.g., Selegiline):** These do not typically cause the cheese reaction at low doses because they spare intestinal MAO-A.

Question 52: Ergot derivatives are used in all of the following conditions except:

A. Uterine contraction
B. Vasoconstrictive disorders (Correct Answer)
C. Migraine
D. Dementia

Explanation: **Explanation:** The correct answer is **B. Vasoconstrictive disorders**. Ergot alkaloids (like Ergotamine and Ergonovine) act as partial agonists at **alpha-adrenergic receptors** and **5-HT receptors**. Their primary vascular effect is **potent vasoconstriction**. Therefore, they are strictly **contraindicated** in vasoconstrictive disorders (e.g., Raynaud’s phenomenon, Buerger’s disease, or Peripheral Vascular Disease) as they would worsen ischemia and potentially lead to gangrene. **Analysis of other options:** * **A. Uterine contraction:** Ergot derivatives like **Methylergonovine** are used in Postpartum Hemorrhage (PPH) because they cause forceful, tetanic uterine contractions (oxytocic effect) to control bleeding. * **C. Migraine:** **Ergotamine** and **Dihydroergotamine (DHE)** are used in acute migraine attacks. They work by constricting dilated cerebral vessels and inhibiting neurogenic inflammation via 5-HT1B/1D receptors. * **D. Dementia:** **Dihydroergotoxine (Codergocrine)** is a mixture of hydrogenated ergot alkaloids used as a nootropic to improve cognitive function in senile dementia by increasing cerebral blood flow and metabolism. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for PPH:** Oxytocin is preferred over Ergometrine because Ergometrine can cause hypertension and is contraindicated in pre-eclampsia. * **Ergotism (St. Anthony’s Fire):** Chronic poisoning characterized by intense vasoconstriction leading to dry gangrene and hallucinations. * **Bromocriptine:** A dopamine agonist ergot derivative used in Parkinson’s disease, Prolactinoma, and Type 2 Diabetes. * **Cabergoline:** Preferred over Bromocriptine for hyperprolactinemia due to its longer half-life and better tolerability.

Question 53: Which alpha-2 agonist is used in the management of glaucoma?

A. Brimonidine (Correct Answer)
B. Timolol
C. Phenylephrine
D. Reserpine

Explanation: **Brimonidine** is a highly selective **alpha-2 (α2) adrenergic agonist** used in the management of open-angle glaucoma [1]. Its mechanism of action is unique because it provides a dual effect: 1. **Decreases aqueous humor production** by causing vasoconstriction of the ciliary body blood vessels [1]. 2. **Increases uveoscleral outflow** (the alternative drainage pathway). Additionally, Brimonidine is noted for its potential **neuroprotective** properties on retinal ganglion cells, making it a high-yield choice for exam questions. **Analysis of Incorrect Options:** * **B. Timolol:** While it is a first-line treatment for glaucoma, it is a **non-selective beta-blocker**, not an alpha-2 agonist [1]. It works solely by reducing aqueous humor production. * **C. Phenylephrine:** This is a selective **alpha-1 agonist**. It is used as a mydriatic (to dilate the pupil) but is generally avoided in glaucoma (especially closed-angle) as it can precipitate an acute attack [1]. * **D. Reserpine:** This is an older antihypertensive that acts as a **vesicular monoamine transporter (VMAT) inhibitor**, depleting catecholamines. It has no role in the topical management of glaucoma. **High-Yield Clinical Pearls for NEET-PG:** * **Apraclonidine** is another α2 agonist used in glaucoma, primarily to prevent post-laser intraocular pressure (IOP) spikes [1]. * **Side Effects:** Brimonidine can cause **follicular conjunctivitis** (allergic reaction) and, in children, it can cross the blood-brain barrier causing **CNS depression and apnea** (Contraindicated in infants). * **Mnemonic:** "Alpha-2 Agonists **A**dd to drainage (**A**praclonidine/**B**rimonidine) and **A**rrest production."

Question 54: Which of the following is a tocolytic agent?

A. Prazosin
B. Ritodrine (Correct Answer)
C. Yohimbine
D. Propranolol

Explanation: **Explanation:** **Correct Option: B. Ritodrine** Tocolytics are drugs used to inhibit uterine contractions to delay premature labor. The uterus contains **$\beta_2$ receptors**, which, when stimulated, lead to smooth muscle relaxation (bronchodilation, vasodilation, and uterine relaxation). **Ritodrine** and **Terbutaline** are selective $\beta_2$ agonists specifically used for their tocolytic effect. By increasing intracellular cAMP, they decrease calcium sensitivity in the myometrium, effectively "quieting" the uterus. **Incorrect Options:** * **A. Prazosin:** This is a selective **$\alpha_1$ blocker** used primarily in the treatment of hypertension and Benign Prostatic Hyperplasia (BPH). It causes vasodilation but has no significant effect on uterine relaxation. * **C. Yohimbine:** This is a selective **$\alpha_2$ blocker**. It was historically used for erectile dysfunction and has no role in managing labor. * **D. Propranolol:** This is a **non-selective $\beta$ blocker**. Since $\beta_2$ stimulation relaxes the uterus, a $\beta$ blocker would theoretically increase uterine tone or interfere with the action of tocolytics, making it contraindicated for this purpose. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Tocolytics:** *"It’s Not My Time"* (**I**ndomethacin, **N**ifedipine, **M**agnesium sulfate, **T**erbutaline/Ritodrine). * **Side Effects of $\beta_2$ Tocolytics:** Maternal tachycardia, palpitations, hypokalemia, and hyperglycemia (due to cross-stimulation of $\beta_1$ and metabolic $\beta_2$ effects). * **Current Trend:** While Ritodrine is the classic textbook answer, **Nifedipine** (Calcium Channel Blocker) and **Atosiban** (Oxytocin antagonist) are now often preferred clinically due to a better side-effect profile.

Question 55: Atropine is used in all of the following conditions EXCEPT:

A. Glaucoma (Correct Answer)
B. Mushroom poisoning
C. Malathion poisoning
D. Organophosphorous poisoning

Explanation: **Explanation:** The correct answer is **A. Glaucoma**. **Why Glaucoma is the Correct Answer:** Atropine is a potent **muscarinic antagonist**. In the eye, it causes **mydriasis** (dilation of the pupil) by blocking the sphincter pupillae and **cycloplegia** (paralysis of accommodation) by blocking the ciliary muscle. In patients with narrow-angle glaucoma, mydriasis causes the iris tissue to bunch up and block the canal of Schlemm, preventing the drainage of aqueous humor. This leads to a dangerous increase in intraocular pressure (IOP). Therefore, Atropine is strictly **contraindicated** in glaucoma. **Analysis of Incorrect Options:** * **B. Mushroom Poisoning:** Certain mushrooms (e.g., *Amanita muscaria*) contain high levels of muscarine, leading to severe cholinergic crisis. Atropine is the specific physiological antagonist used to block these effects. * **C & D. Malathion and Organophosphorous (OP) Poisoning:** Malathion is a type of OP compound. These substances inhibit acetylcholinesterase, leading to an accumulation of acetylcholine. Atropine is the **drug of choice** to reverse the life-threatening muscarinic effects (bradycardia, bronchospasm, and excessive secretions). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Atropine is the DOC for symptomatic sinus bradycardia and OP poisoning. * **Monitoring in OP Poisoning:** Atropine is titrated until "Atropinization" occurs (clearing of chest secretions and heart rate >80 bpm), *not* just pupil dilation. * **Mnemonic for Atropine Toxicity:** "Mad as a hatter (delirium), Red as a beet (flushing), Blind as a bat (mydriasis), Hot as a hare (hyperthermia), and Dry as a bone (decreased secretions)." * **Alternative in Glaucoma:** If a fundus examination is needed in a glaucoma patient, short-acting sympathomimetics like Phenylephrine are preferred over Atropine.

Question 56: Which drug is used to counter the central anticholinergic effect?

A. Physostigmine (Correct Answer)
B. Atropine
C. Neostigmine
D. Hyoscine

Explanation: **Explanation:** The core concept in this question is the ability of a drug to cross the **blood-brain barrier (BBB)**. To counter central anticholinergic effects (such as delirium, hallucinations, or seizures caused by atropine overdose), a drug must be able to enter the Central Nervous System (CNS). **1. Why Physostigmine is Correct:** Physostigmine is a reversible acetylcholinesterase inhibitor. Chemically, it is a **tertiary amine**, which makes it lipid-soluble. This property allows it to cross the BBB and increase acetylcholine levels in the brain, effectively reversing both peripheral and central symptoms of anticholinergic toxicity (the "Antidote of choice"). **2. Why the other options are incorrect:** * **Neostigmine:** Unlike physostigmine, neostigmine is a **quaternary ammonium compound**. It is polar/ionized and cannot cross the BBB. Therefore, it can only reverse peripheral effects (like myasthenia gravis or neuromuscular blockade) but has no effect on central toxicity. * **Atropine:** This is a muscarinic antagonist. Giving atropine would worsen anticholinergic toxicity rather than counter it. * **Hyoscine (Scopolamine):** Like atropine, this is a belladonna alkaloid with potent central anticholinergic properties. It is used to treat motion sickness but would exacerbate toxicity in this context. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** "Tertiary (Physostigmine) goes to the Top (Brain); Quaternary (Neostigmine) stays in the Quarters (Peripheral)." * **Specific Indication:** Physostigmine is specifically used for **Datura poisoning** and **Atropine poisoning**. * **Caution:** Rapid IV administration of physostigmine can cause bradycardia or seizures; it should be administered slowly. * **Other Tertiary Amines:** Rivastigmine and Donepezil (used in Alzheimer’s) also cross the BBB.

Question 57: Which of the following receptors are inotropic?

A. GABAa
B. Nm
C. Nn
D. All of the above (Correct Answer)

Explanation: **Explanation:** The question tests the fundamental classification of receptors into **ionotropic** (ligand-gated ion channels) and **metabotropic** (G-protein coupled receptors). **Ionotropic receptors** are membrane-bound protein complexes that form an ion-conducting pore. When a ligand binds, the channel opens immediately, allowing the flux of ions (like $Na^+$, $K^+$, or $Cl^-$) across the membrane, resulting in rapid excitatory or inhibitory effects. 1. **GABA$_A$:** This is a ligand-gated **chloride ($Cl^-$) channel**. Binding of GABA leads to chloride influx, causing hyperpolarization and rapid neuronal inhibition. (Note: GABA$_B$ is metabotropic/GPCR). 2. **N$_m$ (Muscle-type Nicotinic):** Located at the neuromuscular junction. It is a pentameric ligand-gated **cation channel**. Activation leads to $Na^+$ influx, causing depolarization and skeletal muscle contraction. 3. **N$_n$ (Neuronal-type Nicotinic):** Located in autonomic ganglia and the adrenal medulla. Like N$_m$, it is a ligand-gated **cation channel** that mediates rapid synaptic transmission. Since all three options function via direct ion channel gating, **Option D (All of the above)** is correct. **High-Yield Clinical Pearls for NEET-PG:** * **Speed of Action:** Ionotropic receptors act within milliseconds, whereas metabotropic receptors (GPCRs) take seconds to minutes. * **Other Ionotropic Receptors:** 5-HT$_3$ (the only ionotropic serotonin receptor) and NMDA/AMPA/Kainate (Glutamate receptors). * **Mnemonic:** Remember "**N**icotinic, **G**ABA$_A$, **G**lutamate, and **S**erotonin (5-HT$_3$)" as the primary ionotropic families (**N-G-G-S**). * **GABA$_A$ Pharmacology:** Benzodiazepines and Barbiturates act on the GABA$_A$ receptor to increase the frequency and duration of channel opening, respectively.

Question 58: Which of the following is an anticholinergic used in all EXCEPT?

A. Uveitis
B. Fundus examination
C. Organophosphate poisoning
D. Glaucoma (Correct Answer)

Explanation: Explanation: Anticholinergics (Muscarinic antagonists) like Atropine, Tropicamide [1], and Cyclopentolate are generally **contraindicated in Glaucoma**, particularly Angle-Closure Glaucoma [1], [2]. **1. Why Glaucoma is the Correct Answer:** Anticholinergics cause **Mydriasis** (dilation of the pupil) by blocking the M3 receptors on the sphincter pupillae muscle. In individuals with narrow anterior chamber angles, the iris tissue bunches up toward the periphery during dilation, further obstructing the trabecular meshwork. This prevents the drainage of aqueous humor, leading to a dangerous increase in Intraocular Pressure (IOP) [1], [2]. Additionally, they cause **Cycloplegia** (paralysis of the ciliary muscle), which reduces the tension on the trabecular meshwork, further decreasing drainage. **2. Analysis of Incorrect Options:** * **Uveitis:** Anticholinergics (e.g., Atropine) are used to provide rest to the inflamed ciliary body and to prevent the formation of **synechiae** (adhesions between the iris and lens) by keeping the pupil dilated. * **Fundus Examination:** Short-acting mydriatics like **Tropicamide** [1] are routinely used to dilate the pupil to allow a clear view of the retina and optic disc. * **Organophosphate (OP) Poisoning:** Atropine is the **specific antidote** [1] for the muscarinic effects of OP poisoning (salivation, lacrimation, bradycardia, bronchoconstriction). It is life-saving in this context. **Clinical Pearls for NEET-PG:** * **Drug of choice for Fundus exam:** Tropicamide (fastest onset, shortest duration). * **Drug of choice for Iridocyclitis:** Atropine (long-acting, prevents synechiae). * **Miotics (e.g., Pilocarpine)** are used in Glaucoma, while **Mydriatics** are contraindicated. * **Atropine Flush:** Cutaneous vasodilation seen in atropine overdose (Red as a beet).

Question 59: Which of the following is an alpha 1a selective blocker?

A. Tamsulosin (Correct Answer)
B. Prazosin
C. Yohimbine
D. Idazoxan

Explanation: **Explanation:** The correct answer is **Tamsulosin**. **1. Why Tamsulosin is correct:** Alpha-1 receptors are further divided into subtypes: **$\alpha_{1A}$**, $\alpha_{1B}$, and $\alpha_{1D}$. The $\alpha_{1A}$ subtype is predominantly located in the **smooth muscles of the bladder neck and prostate** [1]. Tamsulosin (and Silodosin) are highly selective $\alpha_{1A}$ blockers [2]. By targeting these specific receptors, they cause relaxation of the prostatic urethra without significantly affecting the $\alpha_{1B}$ receptors found in vascular smooth muscle [1]. This makes them "uroselective," providing relief in **Benign Prostatic Hyperplasia (BPH)** with a minimal risk of orthostatic hypotension [2]. **2. Why the other options are incorrect:** * **Prazosin:** It is a **non-selective $\alpha_1$ blocker** (blocks $\alpha_{1A}$, $\alpha_{1B}$, and $\alpha_{1D}$ equally) [3]. While it can be used for BPH, its primary side effect is the "first-dose phenomenon" (severe postural hypotension) due to its effect on vascular $\alpha_{1B}$ receptors [2]. * **Yohimbine:** It is a selective **$\alpha_2$ blocker** [3]. It was historically used for erectile dysfunction but is rarely used clinically today. * **Idazoxan:** It is also a selective **$\alpha_2$ blocker** primarily used in research settings to study adrenergic neurotransmission. **3. NEET-PG High-Yield Pearls:** * **Silodosin** is even more $\alpha_{1A}$ selective than Tamsulosin but is associated with a higher incidence of **retrograde ejaculation** [2]. * **Floppy Iris Syndrome:** A critical surgical complication during cataract surgery associated with Tamsulosin use; surgeons must be informed if a patient is on this drug. * **Drug of choice for BPH:** Selective $\alpha_{1A}$ blockers are preferred for rapid symptom relief, whereas **5-alpha reductase inhibitors** (e.g., Finasteride) are used to reduce the actual size of the prostate over months.

Question 60: Therapeutic uses of Prostaglandin E1 include all of the following except?

A. Medical termination of pregnancy
B. Erectile dysfunction
C. Primary pulmonary hypertension (Correct Answer)
D. Maintenance of patent ductus arteriosus (PDA)

Explanation: ### Explanation **Correct Option: C. Primary pulmonary hypertension** **Why it is the correct answer:** Prostaglandin E1 (PGE1), also known as **Alprostadil**, is not the drug of choice for Primary Pulmonary Hypertension (PPH). The prostaglandin used for PPH is **Prostacyclin (PGI2)** or its analogs like **Epoprostenol, Iloprost, or Treprostinil**. These agents act as potent pulmonary vasodilators and inhibitors of platelet aggregation, whereas PGE1 is primarily utilized for its effects on smooth muscles in the ductus arteriosus and the corpus cavernosum. **Analysis of Incorrect Options:** * **A. Medical termination of pregnancy (MTP):** **Misoprostol** is a synthetic PGE1 analog. It is used in combination with Mifepristone for MTP because it causes cervical ripening and uterine contractions. * **B. Erectile dysfunction:** **Alprostadil (PGE1)** can be administered via intracavernosal injection or intraurethral suppository. It induces vasodilation and relaxation of the trabecular smooth muscle of the corpus cavernosum, facilitating an erection. * **D. Maintenance of patent ductus arteriosus (PDA):** In neonates with cyanotic heart disease (e.g., Transposition of Great Arteries), **Alprostadil** is used to keep the ductus arteriosus open to maintain systemic or pulmonary blood flow until surgery. **High-Yield Clinical Pearls for NEET-PG:** * **PGE1 (Alprostadil):** Used for PDA maintenance and ED. **Misoprostol** (PGE1 analog) is used for NSAID-induced peptic ulcers and MTP. * **PGE2 (Dinoprostone):** Primarily used for cervical ripening and induction of labor. * **PGF2α (Latanoprost/Carboprost):** Latanoprost is used in Glaucoma; Carboprost is used for Postpartum Hemorrhage (PPH). * **PGI2 (Epoprostenol):** Used in Pulmonary Hypertension and during hemodialysis to prevent clotting.

Practice by Chapter

Cholinergic Agonists

Practice Questions

Cholinergic Antagonists

Practice Questions

Adrenergic Agonists

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Adrenergic Antagonists

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Ganglionic Agents

Practice Questions

Neuromuscular Blocking Agents

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Autonomic Drugs in Ophthalmology

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Autonomic Drugs in Cardiovascular Disease

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Autonomic Drugs in Respiratory Disease

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Autonomic Drugs in Urological Disorders

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