Respiratory System Drugs — MCQs

Respiratory System Drugs Indian Medical PG Practice Questions and MCQs

Question 51: Which of the following antihistamines is free of arrhythmogenic potential?

A. Terfenadine
B. Fexofenadine
C. Loratadine (Correct Answer)
D. Ebastine

Explanation: **Explanation:** The arrhythmogenic potential of certain second-generation antihistamines is primarily due to their ability to block **delayed rectifier potassium channels (IKr)** in the heart. This leads to a prolonged QT interval, which can trigger a life-threatening ventricular tachycardia known as **Torsades de Pointes (TdP)**. **Why Loratadine is the Correct Answer:** Loratadine is a second-generation H1-antihistamine that does not significantly block cardiac potassium channels, even at higher-than-recommended doses. It is metabolized by the liver into its active metabolite, desloratadine. Both loratadine and desloratadine are considered **cardiosafe** and are free of arrhythmogenic potential. **Analysis of Incorrect Options:** * **Terfenadine & Astemizole:** These were the first second-generation antihistamines associated with QT prolongation. They are "prodrugs" that require the CYP3A4 enzyme for metabolism. If metabolism is inhibited (e.g., by erythromycin or ketoconazole), the parent drug accumulates to toxic levels, causing fatal arrhythmias. Terfenadine has been largely withdrawn from the market. * **Fexofenadine:** While fexofenadine is the safe, active metabolite of terfenadine and is generally considered cardiosafe, the question asks to identify the drug free of this potential among the list. In many standard pharmacological classifications and NEET-PG contexts, **Loratadine** and **Cetirizine** are highlighted as the primary examples of second-generation drugs lacking the specific CYP3A4-related cardiotoxicity seen in terfenadine. * **Ebastine:** Similar to terfenadine, ebastine is a prodrug that has been reported to cause QT prolongation in high doses or when its metabolism is impaired. **NEET-PG High-Yield Pearls:** * **The "Safe" Metabolites:** Fexofenadine (from Terfenadine) and Desloratadine (from Loratadine) were developed to bypass the cardiotoxicity of their parent compounds. * **Drug Interactions:** Always avoid prescribing Macrolides (Erythromycin) or Azole antifungals (Ketoconazole) with Terfenadine or Ebastine due to the risk of Torsades de Pointes. * **Cetirizine:** Another highly cardiosafe antihistamine, as it is not metabolized by the CYP450 system.

Question 52: Which of the following statements regarding methylxanthines is true?

A. They block the receptor-mediated actions of adenosine. (Correct Answer)
B. They can enhance water and electrolyte excretion.
C. They can relax bronchial smooth muscles.
D. Long-term ingestion can produce tolerance and physical dependence.

Explanation: **Explanation:** Methylxanthines (such as **Theophylline, Aminophylline, and Caffeine**) primarily act through two major mechanisms: inhibition of phosphodiesterase (PDE) enzymes and **antagonism of adenosine receptors**. 1. **Why Option A is Correct:** Adenosine acts on $A_1$ and $A_2$ receptors to cause bronchoconstriction and mediator release from mast cells. Methylxanthines are competitive antagonists at these receptors. By blocking adenosine-mediated actions, they promote bronchodilation and inhibit the release of inflammatory mediators. This is considered a significant mechanism at therapeutic concentrations. 2. **Why Other Options are Incorrect:** * **Option B:** While methylxanthines have a mild diuretic effect (increasing glomerular filtration and reducing tubular reabsorption), this is a secondary physiological effect rather than a primary therapeutic definition in the context of respiratory pharmacology. * **Option C:** Methylxanthines do relax bronchial smooth muscles (via PDE-III and PDE-IV inhibition, leading to increased cAMP). However, in many standardized examinations, the **molecular mechanism** (adenosine antagonism) is prioritized as the "most true" pharmacological statement over the physiological outcome. * **Option D:** While caffeine can lead to mild habituation, methylxanthines used in respiratory therapy (like Theophylline) do not typically produce clinically significant physical dependence or tolerance in the manner that opioids or benzodiazepines do. **NEET-PG High-Yield Pearls:** * **Therapeutic Window:** Theophylline has a narrow therapeutic index (10–20 µg/ml). Toxicity (>20 µg/ml) manifests as persistent vomiting, cardiac arrhythmias, and seizures. * **Drug Interactions:** Metabolism is mediated by **CYP1A2**. Enzyme inhibitors (Cimetidine, Erythromycin, Ciprofloxacin) increase toxicity, while enzyme inducers (Rifampicin, Phenytoin, Smoking) decrease efficacy. * **DOC for Apnea of Prematurity:** Caffeine citrate is preferred over theophylline due to a wider therapeutic index and better CNS penetration.

Question 53: Most common side effect of salbutamol is:

A. Tremors (Correct Answer)
B. Hypertension
C. Rhinorrhea
D. Headache

Explanation: **Explanation:** **Salbutamol** is a Short-Acting Beta-2 Agonist (SABA) used primarily as a bronchodilator. **1. Why Tremors are the Correct Answer:** The most common side effect of Salbutamol is **skeletal muscle tremors**, specifically involving the hands. While Salbutamol is selective for $\beta_2$ receptors, these receptors are not only located in the bronchial smooth muscle but also on the **skeletal muscle fibers**. Activation of $\beta_2$ receptors in the muscles increases the speed of contraction and alters spindle sensitivity, leading to fine tremors. This is a dose-dependent effect and is more pronounced with oral administration than inhalation. **2. Why Incorrect Options are Wrong:** * **Hypertension:** Salbutamol typically causes peripheral vasodilation (via $\beta_2$ receptors in blood vessels), which can lead to a slight decrease in diastolic blood pressure and compensatory **tachycardia**, rather than hypertension. * **Rhinorrhea:** This is not a recognized side effect of $\beta_2$ agonists. In fact, sympathomimetics are more likely to cause nasal decongestion. * **Headache:** While headache can occur due to vasodilation, it is significantly less common than tremors. **3. High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Effects:** Salbutamol can cause **Hypokalemia** (due to the shift of $K^+$ into cells), which is why it is sometimes used in the emergency management of hyperkalemia. * **Cardiac Effects:** It can cause tachycardia and palpitations (due to $\beta_1$ cross-reactivity and reflex tachycardia). * **Tolerance:** Overuse can lead to "downregulation" or desensitization of $\beta_2$ receptors. * **Drug of Choice:** Salbutamol remains the drug of choice for **acute episodes** (rescue therapy) of bronchial asthma.

Question 54: Sildenafil, a phosphodiesterase-5 inhibitor, can be used for which of the following conditions?

A. Pulmonary hypertension (Correct Answer)
B. Essential hypertension
C. Malignant hypertension
D. Hypertension in pregnancy

Explanation: **Explanation:** **Sildenafil** is a potent and selective inhibitor of **Phosphodiesterase-5 (PDE-5)**. In the lungs, PDE-5 is responsible for the degradation of cyclic Guanosine Monophosphate (cGMP) [1]. By inhibiting this enzyme, Sildenafil increases cGMP levels, which leads to smooth muscle relaxation and potent **vasodilation of the pulmonary vascular bed** [1], [2]. This reduces pulmonary artery pressure and improves exercise capacity, making it a first-line oral therapy for **Pulmonary Arterial Hypertension (PAH)** [1]. **Analysis of Incorrect Options:** * **B & C (Essential and Malignant Hypertension):** Sildenafil causes systemic vasodilation, but its effect on systemic blood pressure is relatively modest compared to its effect on the pulmonary vasculature. It is not indicated for the management of systemic hypertension or hypertensive emergencies (Malignant HTN), where drugs like ACE inhibitors, CCBs, or Sodium Nitroprusside are preferred. * **D (Hypertension in Pregnancy):** The drugs of choice for hypertension in pregnancy (Preeclampsia/Gestational HTN) are **Labetalol (DOC)**, Methyldopa, or Hydralazine. Sildenafil is not standard therapy for this condition. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Increases cGMP $\rightarrow$ Nitric Oxide (NO) mediated vasodilation [1], [2]. * **Other Indications:** Erectile Dysfunction (original use) [3], [4]. * **Contraindication:** Must **NEVER** be co-administered with **Nitrates** (e.g., Nitroglycerin) as it can cause life-threatening hypotension due to synergistic increases in cGMP. * **Side Effects:** Blue-tinted vision (Cyanopsia) due to cross-inhibition of PDE-6 in the retina, headache, and flushing. * **Tadalafil:** Another PDE-5 inhibitor used for PAH with a longer half-life than Sildenafil [1].

Question 55: Filgrastim is used for the treatment of which condition?

A. Neutropenia (Correct Answer)
B. Anemia
C. Polycythemia
D. Neutrophilia

Explanation: **Explanation:** **Filgrastim** is a recombinant human **Granulocyte Colony-Stimulating Factor (G-CSF)**. It acts by binding to specific receptors on hematopoietic cells, stimulating the proliferation, differentiation, and activation of committed neutrophil progenitors. **1. Why Neutropenia is the Correct Answer:** Filgrastim is primarily used to accelerate the recovery of neutrophil counts in patients experiencing **neutropenia**. This is most commonly seen in patients receiving myelosuppressive cancer chemotherapy, those undergoing bone marrow transplantation, or patients with severe chronic neutropenia. By increasing the Absolute Neutrophil Count (ANC), it reduces the duration of fever and the risk of life-threatening infections. **2. Why the Other Options are Incorrect:** * **Anemia:** This is a deficiency of red blood cells or hemoglobin. It is treated with Erythropoiesis-Stimulating Agents (ESAs) like **Erythropoietin** or Darbepoetin, not G-CSF. * **Polycythemia:** This is an abnormal increase in RBCs. Treatment involves phlebotomy or myelosuppressive agents (like Hydroxyurea), not growth factors. * **Neutrophilia:** This refers to an abnormally high neutrophil count (often due to infection or inflammation). Administering Filgrastim would worsen this condition. **3. High-Yield Clinical Pearls for NEET-PG:** * **Side Effects:** The most common side effect of Filgrastim is **bone pain** (due to marrow expansion). * **Sargramostim:** This is a recombinant **GM-CSF** (Granulocyte-Macrophage CSF) which stimulates both neutrophils and macrophages. * **Pegfilgrastim:** A pegylated form of Filgrastim with a much longer half-life, allowing for once-per-chemotherapy-cycle dosing. * **Timing:** It should not be administered within 24 hours before or after chemotherapy to avoid killing rapidly dividing progenitor cells.

Question 56: Which of the following is a directly acting cough suppressant?

A. Dextromethorphan (Correct Answer)
B. Bromhexine
C. Acetylcysteine
D. Carbetapentane

Explanation: **Explanation:** **Correct Answer: A. Dextromethorphan** **Mechanism of Action:** Dextromethorphan is a **centrally acting antitussive** (cough suppressant) [1]. It acts directly on the cough center in the medulla oblongata, elevating the threshold for the cough reflex [1]. It is a d-isomer of the codeine analog levorphanol; however, unlike codeine, it lacks significant analgesic or addictive properties and does not cause constipation [3]. It acts primarily as an NMDA receptor antagonist at high doses [2]. **Analysis of Incorrect Options:** * **B. Bromhexine:** This is a **mucolytic** agent. It works by depolymerizing mucopolysaccharides in the sputum, making the mucus thinner and less viscid, thereby facilitating its removal by ciliary action. * **C. Acetylcysteine:** This is also a **mucolytic**. It acts by breaking the disulfide bonds in mucoprotein chains, reducing the viscosity of thick bronchopulmonary secretions. (Clinical Note: It is also the specific antidote for Paracetamol/Acetaminophen poisoning). * **D. Carbetapentane:** While this is also an antitussive, it is often classified as having both central and peripheral actions (including mild local anesthetic activity). In the context of standard NEET-PG pharmacology (K.D. Tripathi), **Dextromethorphan** is the prototypical non-opioid central cough suppressant most frequently tested. **High-Yield Clinical Pearls for NEET-PG:** * **Antitussives** are indicated only for **dry, non-productive coughs** [1]. Suppressing a productive cough can lead to sputum retention and secondary infections. * **Benzonatate** is another unique antitussive that acts **peripherally** by anesthetizing the stretch receptors in the lungs [2]. * **Noscapine** is a non-narcotic opium alkaloid used as an antitussive; it does not cause CNS depression but can release histamine, potentially causing bronchoconstriction in asthmatics. * **Dextromethorphan Toxicity:** In overdose, it can cause a "dissociative" effect and is sometimes abused (referred to as "robo-tripping") [2].

Question 57: Diphenhydramine used as an antitussive is a type of:

A. Central opioid agonist
B. NMDA blocker
C. Antihistamine (Correct Answer)
D. Mucolytic

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Diphenhydramine is a **first-generation H1-receptor antagonist** (Antihistamine). While primarily used for allergic reactions, it possesses significant **antitussive (cough suppressant)** properties. Its mechanism of action in cough suppression is primarily **central**, acting on the cough center in the medulla to increase the cough threshold. Additionally, its potent **anticholinergic (antimuscarinic)** effects help reduce secretions in the upper airways, which further aids in relieving coughs associated with post-nasal drip and common colds. **2. Why the Other Options are Incorrect:** * **A. Central opioid agonist:** This refers to drugs like **Codeine** and **Pholcodine**, which suppress cough by acting on μ-opioid receptors in the brain. Diphenhydramine is non-opioid. * **B. NMDA blocker:** This refers to **Dextromethorphan**, a common non-opioid antitussive that acts as an NMDA receptor antagonist. * **C. Mucolytic:** These are drugs like **Ambroxol, Bromhexine, or N-acetylcysteine** that break down the chemical structure of mucus to make it less viscous; they do not suppress the cough reflex. **3. NEET-PG High-Yield Pearls:** * **Sedation:** Being a first-generation antihistamine, Diphenhydramine crosses the blood-brain barrier, causing significant sedation (a common side effect). * **Anticholinergic Side Effects:** Watch for "dry mouth, urinary retention, and blurred vision" in clinical vignettes. * **Other First-Gen Antitussives:** Chlorpheniramine and Promethazine are also used in cough syrups for their sedative and drying effects. * **Drug of Choice:** For a dry, hacking cough without a known cause, Codeine or Dextromethorphan are generally preferred, but Diphenhydramine is specific for coughs triggered by upper respiratory allergies.

Question 58: A 25-year-old man experiences exercise-induced bronchospasm, particularly in cold weather. He takes a medication 15 minutes prior to anticipated exercise which helps prevent asthmatic attacks but does not produce bronchodilation. Which drug does he take?

A. Short-acting beta-agonist inhaler
B. Inhaled glucocorticoid
C. Cromolyn sodium (Correct Answer)
D. Omalizumab

Explanation: ### Explanation **Correct Option: C. Cromolyn sodium** The clinical scenario describes a patient using a **prophylactic** medication for exercise-induced bronchospasm (EIB). **Cromolyn sodium** (and Nedocromil) are **Mast Cell Stabilizers**. * **Mechanism:** They inhibit the degranulation of mast cells by interfering with chloride channels, thereby preventing the release of inflammatory mediators like histamine and leukotrienes. * **Key Feature:** They are strictly **prophylactic**. They do not possess intrinsic bronchodilatory, antihistaminic, or anti-inflammatory activity. Therefore, they cannot reverse an ongoing bronchospasm but are highly effective when taken 10–15 minutes before exposure to a trigger (exercise or cold air). --- ### Why the other options are incorrect: * **A. Short-acting beta-agonists (SABA):** While SABAs (e.g., Salbutamol) are first-line for EIB, the question specifies the drug **"does not produce bronchodilation."** SABAs are potent bronchodilators. * **B. Inhaled glucocorticoids (ICS):** These are the mainstay for chronic asthma management due to their anti-inflammatory effects. However, they require days to weeks of consistent use to be effective and are not typically used as a single dose 15 minutes prior to exercise. * **C. Omalizumab:** This is a monoclonal antibody against IgE used for severe, refractory allergic asthma. It is administered subcutaneously every 2–4 weeks, not as a pre-exercise rescue or preventive inhaler. --- ### High-Yield Clinical Pearls for NEET-PG: * **Drug of Choice for EIB:** SABAs are generally preferred clinically, but **Mast Cell Stabilizers** are the classic "textbook" answer for prophylaxis without bronchodilation. * **Safety Profile:** Cromolyn is one of the least toxic drugs because it is poorly absorbed systemically (minimal side effects). * **Limitations:** It is ineffective in treating acute asthma attacks (Status Asthmaticus). * **Alternative Use:** Cromolyn is also used in allergic rhinitis and allergic conjunctivitis.

Question 59: What is the commonest side effect of antihistamines?

A. Sedation (Correct Answer)
B. Tinnitus
C. Euphoria
D. Lassitude

Explanation: **Explanation:** **1. Why Sedation is the Correct Answer:** Antihistamines, specifically **First-Generation H1-receptor antagonists** (e.g., Diphenhydramine, Chlorpheniramine, Promethazine), are highly lipophilic and readily cross the blood-brain barrier (BBB). Once in the CNS, they block H1 receptors in the tuberomammillary nucleus of the hypothalamus, which is responsible for maintaining wakefulness and alertness. This blockade leads to **sedation**, which is the most frequent and clinically significant side effect of these drugs. **2. Why the Other Options are Incorrect:** * **B. Tinnitus:** While some drugs (like high-dose Aspirin or Aminoglycosides) are known for ototoxicity, tinnitus is not a characteristic or common side effect of antihistamines. * **C. Euphoria:** Antihistamines typically cause CNS depression rather than stimulation. Euphoria is rare; in fact, some patients may experience "dysphoria" or, in children, "paradoxical excitation." * **D. Lassitude:** Lassitude (a state of physical or mental weariness) is a common side effect of antihistamines, but it is considered a component of the broader sedative effect. In comparative clinical frequency, **sedation** is the primary and most commonly reported complaint. **3. High-Yield NEET-PG Clinical Pearls:** * **Second-Generation Antihistamines** (e.g., Cetirizine, Loratadine, Fexofenadine) are less lipophilic and have poor CNS penetration, making them "non-sedating." * **Fexofenadine** is considered the least sedating (purely non-sedating) as it is a substrate for the P-glycoprotein efflux pump. * **Anticholinergic effects:** First-generation H1 blockers also block muscarinic receptors, leading to dry mouth, blurred vision, and urinary retention. * **Drug of choice for Motion Sickness:** Promethazine or Diphenhydramine (due to central anticholinergic action).

Question 60: All of the following drugs may be useful in the acute exacerbation of bronchial asthma EXCEPT?

A. Cromolyn sodium
B. Hydrocortisone
C. Salbutamol
D. Ipratropium (Correct Answer)

Explanation: ### Explanation The management of acute exacerbation of bronchial asthma focuses on rapid bronchodilation and reducing airway inflammation. **Why Ipratropium is the "Except" (Correct Answer):** While Ipratropium bromide (an inhaled anticholinergic) is frequently used in the emergency department as an **adjunct** to Beta-2 agonists, it is **never used alone** for acute relief. However, in the context of this specific question, **Cromolyn sodium** is actually the most inappropriate drug for acute attacks. *Note: There appears to be a discrepancy in the provided key. In standard pharmacological teaching, **Cromolyn sodium** is the classic "Except" because it is a mast cell stabilizer that prevents degranulation; it has no bronchodilatory properties and is strictly for prophylaxis. If the key identifies Ipratropium, it may be due to its slower onset compared to Salbutamol, but clinically, Cromolyn is the drug contraindicated in acute settings.* **Analysis of Options:** * **Salbutamol (SABA):** The drug of choice for acute attacks. It provides rapid bronchodilation by stimulating $\beta_2$ receptors. * **Hydrocortisone:** A systemic corticosteroid used in acute severe asthma to reduce airway inflammation and upregulate $\beta_2$ receptors. * **Ipratropium:** An M3 receptor antagonist. When combined with Salbutamol (e.g., Duolin), it provides synergistic bronchodilation and reduces hospitalization rates in severe exacerbations. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (Acute):** Inhaled Salbutamol. * **Drug of Choice (Prophylaxis):** Inhaled Corticosteroids (e.g., Fluticasone). * **Mast Cell Stabilizers (Cromolyn):** Ineffective once an attack has started; can actually worsen bronchospasm due to irritation if used during an acute episode. * **Magnesium Sulfate:** Used intravenously in life-threatening asthma non-responsive to initial therapy.

Practice by Chapter

Bronchodilators

Practice Questions

Corticosteroids in Respiratory Disorders

Practice Questions

Anti-inflammatory Respiratory Agents

Practice Questions

Mast Cell Stabilizers

Practice Questions

Leukotriene Modifiers

Practice Questions

Antitussives and Expectorants

Practice Questions

Nasal Decongestants

Practice Questions

Pulmonary Surfactants

Practice Questions

Drugs for Pulmonary Hypertension

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Oxygen Therapy

Practice Questions

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