Autonomic Nervous System Drugs Practice Questions

Q: Which of the following drugs should be given in a patient with acute angle closure glaucoma, except?

Pilocarpine. **Explanation:** Acute Angle-Closure Glaucoma (AACG) is an ophthalmic emergency characterized by a rapid increase in intraocular pressure (IOP) due to the blockage of the drainage angle. The primary goal of treatment is to induce **miosis** (pupillary constriction) to pull the iris away from the trabecular meshwork, thereby opening the angle and facilitating aqueous humor outflow. **Why Pilocarpine is the Correct Answer:** **Pilocarpine** is a direct-acting cholinergic agonist (miotic). It acts on the $M_3$ receptors of the sphincter pupillae muscle, causing miosis. This physical movement of the iris clears the iridocorneal angle, making it the drug of choice for the emergency management of AACG. **Analysis of Incorrect Options (Drugs to be avoided):** The other options are drugs with **anticholinergic (atropine-like) properties**, which are strictly contraindicated in AACG: * **Clozapine:** An atypical antipsychotic with significant muscarinic antagonist activity. * **Fluphenazine:** A typical antipsychotic (phenothiazine) that possesses anticholinergic side effects. * **Paroxetine:** An SSRI that, unlike others in its class, has mild but clinically relevant anticholinergic effects. * **Mechanism of Danger:** Anticholinergic drugs cause **mydriasis** (pupillary dilation). In a predisposed eye, dilation causes the iris to bunch up at the periphery, further narrowing the angle and potentially precipitating a crisis of acute glaucoma. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for AACG:** IV Acetazolamide (to reduce production) + Topical Pilocarpine (to increase drainage). * **Definitive Treatment:** Peripheral Iridotomy (Laser). * **Mydriatics to avoid in Glaucoma:** Atropine, Cyclopentolate, and Tricyclic Antidepressants (TCAs). * **Pilocarpine Side Effect:** Can cause "brow ache" due to ciliary muscle contraction (accommodative spasm).

Q: In oral poisoning with carbamate insecticide, which of the following may be hazardous?

Pralidoxime. **Explanation:** The correct answer is **A. Pralidoxime**. **1. Why Pralidoxime is hazardous in Carbamate poisoning:** Carbamates (e.g., Neostigmine, Physostigmine, Carbaryl) cause reversible inhibition of acetylcholinesterase (AChE) by carbamylation of the enzyme's esteratic site [1]. Unlike organophosphates (OP), carbamates do not undergo "aging." Pralidoxime (an oxime) is a cholinesterase reactivator designed to displace the phosphate group in OP poisoning [2]. However, in carbamate poisoning, the enzyme-carbamate bond is transient and dissociates spontaneously. Adding Pralidoxime can be hazardous because: * Oximes themselves have weak anticholinesterase activity, which can worsen the cholinergic crisis. * Specifically, in **Carbaryl** poisoning, oximes significantly increase the toxicity of the carbamate. **2. Why other options are incorrect:** * **B. Atropine:** This is the **drug of choice** for carbamate poisoning. It competitively antagonizes the muscarinic effects of accumulated acetylcholine. * **C. Magnesium sulfate purgative:** Used to hasten the elimination of the unabsorbed poison from the GI tract. It is a standard supportive measure. * **D. Gastric lavage with activated charcoal:** This is a standard decontamination procedure to prevent further absorption of the toxin if the patient presents within the "golden hour." **Clinical Pearls for NEET-PG:** * **Rule of Thumb:** "Atropine for all, Oximes for OP only." * **Exception:** While oximes are generally contraindicated in carbamates, some guidelines suggest they may be used if there is a **mixed poisoning** (OP + Carbamate) or if the specific toxin is unknown, provided Atropine is already administered. * **Key Difference:** Carbamates = Reversible inhibition (No aging); Organophosphates = Irreversible inhibition (Aging occurs).

Q: Which of the following can be blocked by atropine, a muscarinic receptor blocker?

Bradycardia caused by infusion of acetylcholine. **Explanation:** **1. Why Option C is Correct:** Atropine is a competitive antagonist of **muscarinic receptors (M1–M5)**. Acetylcholine (ACh) acts on M2 receptors located in the SA and AV nodes of the heart to cause a decrease in heart rate (bradycardia). Since atropine specifically blocks these muscarinic receptors, it prevents ACh from binding, thereby blocking the bradycardic effect. **2. Why Other Options are Incorrect:** * **Option A:** Nicotine increases blood pressure by stimulating **Nicotinic neuronal (Nn) receptors** in the autonomic ganglia and the adrenal medulla (releasing adrenaline). Atropine has no effect on nicotinic receptors; therefore, it cannot block nicotine-induced hypertension. * **Option B:** Neostigmine increases ACh levels at the neuromuscular junction. This ACh acts on **Nicotinic muscle (Nm) receptors** to increase skeletal muscle strength. Atropine does not block Nm receptors (which require neuromuscular blockers like d-tubocurarine). Thus, atropine does not reverse the skeletal muscle effects of cholinesterase inhibitors. * **Option D:** Since options A and B involve nicotinic receptors, this option is incorrect. **Clinical Pearls for NEET-PG:** * **Atropine Flush:** High doses of atropine cause cutaneous vasodilation (atropine flush), though the mechanism is not fully understood (likely non-cholinergic). * **Drug of Choice:** Atropine is the DOC for **symptomatic bradycardia** and **organophosphate poisoning** (to reverse muscarinic symptoms like salivation, lacrimation, and bronchoconstriction). * **Mnemonic for Atropine Toxicity:** "Hot as a hare, red as a beet, dry as a bone, blind as a bat, and mad as a hatter."

Q: Which of the following is an example of asymmetric mixed-onium chlorofumarate?

Gantacurium. **Explanation:** **Gantacurium** is the correct answer because it belongs to a new class of neuromuscular blocking agents known as **asymmetric mixed-onium chlorofumarates**. Chemically, it is a fumaric acid ester that contains two different (asymmetric) ammonium groups. It was developed to provide an ultra-short duration of action with a rapid onset, similar to Succinylcholine but without the side effects of depolarization. Its metabolism is unique, occurring via rapid non-enzymatic degradation (cysteine adduction) and ester hydrolysis. **Analysis of Incorrect Options:** * **Rocuronium:** An aminosteroid compound. It is an intermediate-acting non-depolarizing agent known for the fastest onset among non-depolarizing drugs, making it suitable for rapid sequence induction. * **Vecuronium:** Also an aminosteroid derivative. It is an intermediate-acting agent that does not cause significant histamine release or cardiovascular instability. * **Atracurium:** A benzylisoquinolinium compound. It is famous for undergoing **Hofmann elimination** (spontaneous molecular degradation), making it safe for patients with renal or hepatic failure. **High-Yield Clinical Pearls for NEET-PG:** * **Gantacurium's** ultra-short duration is its defining feature; it is currently being studied as a non-depolarizing alternative to Succinylcholine. * **Mivacurium** is the shortest-acting *currently used* non-depolarizing blocker, metabolized by plasma cholinesterase. * **Sugammadex** is a specific reversal agent for aminosteroids (Rocuronium > Vecuronium) but has **no effect** on Gantacurium or Atracurium. * **Laudanosine** is a toxic metabolite of Atracurium that can cross the BBB and potentially cause seizures.

Q: Beta 2 selective agonists are often effective in which of the following conditions?

Asthma. **Explanation:** **1. Why Option B is Correct:** Beta-2 ($\beta_2$) receptors are primarily located in the smooth muscles of the bronchi, blood vessels, and uterus. Activation of these G-protein coupled receptors leads to an increase in intracellular cAMP, which causes **smooth muscle relaxation**. In **Asthma**, $\beta_2$ selective agonists (like Salbutamol or Terbutaline) induce bronchodilation, rapidly relieving airway obstruction. This makes them the mainstay for treating acute bronchospasm. **2. Why Other Options are Incorrect:** * **Option A (Angina):** $\beta_2$ agonists are not used in angina. In fact, $\beta$-blockers (especially $\beta_1$ blockers) are the standard treatment for angina as they decrease myocardial oxygen demand. Non-selective $\beta$ agonists could potentially worsen angina by causing reflex tachycardia. * **Option C (Delayed Labor):** This is a common distractor. $\beta_2$ agonists (e.g., Ritodrine, Isoxsuprine) cause uterine relaxation (tocolysis). Therefore, they are used to **arrest premature labor**, not to treat "delayed labor." To treat delayed labor, one would use uterine stimulants like Oxytocin. **3. High-Yield Clinical Pearls for NEET-PG:** * **Tocolytics:** Ritodrine and Terbutaline are specific $\beta_2$ agonists used to delay preterm labor. * **Side Effects:** The most common side effect of $\beta_2$ agonists is **muscle tremors** (due to action on $\beta_2$ receptors in skeletal muscles). Other effects include tachycardia (due to $\beta_1$ cross-reactivity and reflex action) and **hypokalemia** (as they drive $K^+$ into cells). * **Classification:** * **SABA (Short-Acting):** Salbutamol, Levosalbutamol (Rescue therapy). * **LABA (Long-Acting):** Salmeterol, Formoterol (Maintenance therapy).

Q: Which of the following drugs is used in this test?

Tolazoline. ***Tolazoline*** - **Tolazoline** is an **alpha-adrenergic blocker** used as a pharmacological adjunct in **Meckel's diverticulum scintigraphy** to inhibit the release of **Tc-99m pertechnetate** from ectopic gastric mucosa. - By blocking gastric acid secretion, it enhances **visualization** of the Meckel's diverticulum by allowing greater accumulation of the radiotracer in the ectopic gastric tissue. *Clonidine* - **Clonidine** is an **alpha-2 agonist** used primarily for **hypertension** and **ADHD**, not for nuclear medicine imaging studies. - It has no role in **Meckel's diverticulum scintigraphy** and would not enhance visualization of ectopic gastric mucosa. *Bismuth* - **Bismuth** compounds are used for **H. pylori eradication** and as **antidiarrheal agents**, not in nuclear imaging procedures. - It would interfere with **Tc-99m pertechnetate** uptake rather than enhance visualization in Meckel's scan. *Oxymetazoline* - **Oxymetazoline** is an **alpha-1 agonist** used as a **nasal decongestant** with vasoconstrictor properties. - It has no application in **nuclear medicine** and would not be beneficial for enhancing Meckel's diverticulum visualization.

Q: Which of the following inhibits the rate-limiting step of norepinephrine synthesis?

Metyrosine. ### Explanation **Correct Answer: C. Metyrosine** The synthesis of norepinephrine (NE) follows a specific metabolic pathway: **Tyrosine → DOPA → Dopamine → Norepinephrine → Epinephrine.** The **rate-limiting step** in this sequence is the conversion of Tyrosine to DOPA, catalyzed by the enzyme **Tyrosine Hydroxylase**. **Metyrosine** (α-methyl-L-tyrosine) acts as a competitive inhibitor of this enzyme. By blocking the very first step, it effectively depletes the stores of catecholamines in the nerve endings. --- ### Analysis of Incorrect Options: * **A. Cocaine:** It does not inhibit synthesis. Instead, it inhibits **Uptake-1** (the neuronal reuptake transporter), leading to increased concentrations of NE in the synaptic cleft. * **B. Amphetamine:** It acts primarily as an **indirect sympathomimetic**. It displaces NE from storage vesicles into the cytosol and reverses the NET transporter, causing a massive release of NE into the synapse. * **C. Bretylium:** This is an **adrenergic neuron blocker**. It inhibits the release of NE from the nerve terminal into the synapse (similar to Guanethidine) and also has Class III antiarrhythmic properties. --- ### High-Yield NEET-PG Pearls: * **Clinical Use of Metyrosine:** It is primarily used for the preoperative management of **Pheochromocytoma** to reduce catecholamine production and prevent hypertensive crises during surgery. * **VMAT Inhibition:** While Metyrosine inhibits synthesis, **Reserpine** inhibits the storage of NE by blocking the Vesicular Monoamine Transporter (VMAT). * **Final Step:** The conversion of Dopamine to NE occurs *inside* the storage vesicles via **Dopamine β-hydroxylase**. * **Rate-limiting enzyme mnemonic:** Remember **T**yrosine **H**ydroxylase is the **T**op **H**urdle (Rate-limiting).

Question 1

Which of the following properties makes pyridostigmine different from neostigmine?

Accepted Answer

It is longer acting

Answer

It is more potent

Answer

It produces fewer muscarinic side effects

Answer

It has no direct action on neuromuscular receptors

Question 2

Which of the following H1 blockers has high anticholinergic activity?

Accepted Answer

Chlorpheniramine

Answer

Cetirizine

Answer

Fexofenadine

Answer

Astemizole

Question 3

Which of the following drugs should be given in a patient with acute angle closure glaucoma, except?

Accepted Answer

Pilocarpine

Answer

Clozapine

Answer

Fluphenazine

Answer

Paroxetine

Question 4

In oral poisoning with carbamate insecticide, which of the following may be hazardous?

Accepted Answer

Pralidoxime

Answer

Atropine

Answer

Magnesium sulfate purgative

Answer

Gastric lavage with activated charcoal

Question 5

Which of the following can be blocked by atropine, a muscarinic receptor blocker?

Accepted Answer

Bradycardia caused by infusion of acetylcholine

Answer

Increased blood pressure caused by nicotine

Answer

Increased skeletal muscle strength caused by neostigmine, an acetylcholinesterase inhibitor

Answer

All of these

Question 6

Which of the following is an example of asymmetric mixed-onium chlorofumarate?

Accepted Answer

Gantacurium

Answer

Rocuronium

Answer

Vecuronium

Answer

Atracurium

Question 7

Beta 2 selective agonists are often effective in which of the following conditions?

Accepted Answer

Asthma

Answer

Angina due to coronary insufficiency

Answer

Delayed labor

Answer

All the above

Question 8

Which of the following drugs is used in this test?

Accepted Answer

Tolazoline

Answer

Clonidine

Answer

Bismuth

Answer

Oxymetazoline

Question 9

What is the most important action of beta-blockers in glaucoma?

Accepted Answer

Decrease in the production of aqueous humor

Answer

Membrane stabilizing effect

Answer

Retinal neuron protecting effect

Answer

Pupillary constriction

Question 10

Which of the following inhibits the rate-limiting step of norepinephrine synthesis?

Accepted Answer

Metyrosine

Answer

Cocaine

Answer

Amphetamine

Answer

Bretylium

Autonomic Nervous System Drugs — MCQs

Autonomic Nervous System Drugs — MCQs

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