Respiratory System Drugs — MCQs

Respiratory System Drugs Indian Medical PG Practice Questions and MCQs

Question 31: What is the only FDA-approved application of inhaled nitric oxide?

A. Primary pulmonary hypertension
B. Newborn with persistent pulmonary hypertension (Correct Answer)
C. Congestive cardiac failure
D. High-altitude pulmonary edema (HAPE)

Explanation: ### Explanation **Correct Option: B. Newborn with persistent pulmonary hypertension (PPHN)** Inhaled Nitric Oxide (iNO) is a potent, selective pulmonary vasodilator. Its primary mechanism involves the activation of soluble guanylyl cyclase, increasing cGMP levels in vascular smooth muscle, which leads to relaxation. The FDA has approved iNO specifically for **term and near-term neonates (>34 weeks gestation)** with hypoxic respiratory failure associated with **Persistent Pulmonary Hypertension of the Newborn (PPHN)**. It improves oxygenation and reduces the need for extracorporeal membrane oxygenation (ECMO). **Analysis of Incorrect Options:** * **A. Primary Pulmonary Hypertension (PAH):** While iNO is used during "vasoreactivity testing" to identify patients who might respond to Calcium Channel Blockers, it is not an approved long-term treatment. Chronic PAH is managed with Bosentan (Endothelin antagonist), Sildenafil (PDE-5 inhibitor), or Epoprostenol (Prostacyclin). * **C. Congestive Cardiac Failure (CCF):** iNO is not indicated for CCF. In fact, in patients with pre-existing left ventricular dysfunction, iNO can increase pulmonary venous return, potentially worsening pulmonary edema. * **D. High-altitude Pulmonary Edema (HAPE):** The standard of care for HAPE is immediate descent and supplemental oxygen. While vasodilators like Nifedipine or Tadalafil are used for prevention/treatment, iNO is not an FDA-approved indication for this condition. **NEET-PG High-Yield Pearls:** * **Selectivity:** iNO is "selective" because it only dilates vessels in ventilated areas of the lung (improving V/Q matching) and is rapidly inactivated by hemoglobin, preventing systemic hypotension. * **Toxicity:** Monitor for **Methemoglobinemia** and Nitrogen dioxide ($NO_2$) levels during administration. * **Rebound Effect:** Abrupt withdrawal of iNO can cause rebound pulmonary hypertension; therefore, it must be tapered gradually.

Question 32: Which leukotriene receptor antagonist is used for bronchial asthma?

A. Zafirlukast (Correct Answer)
B. Zileuton
C. Cromolyn Sodium
D. Aminophylline

Explanation: **Explanation:** **Correct Answer: A. Zafirlukast** Leukotrienes (specifically Cysteinyl Leukotrienes: $LTC_4, LTD_4, LTE_4$) are potent bronchoconstrictors and mediators of inflammation in asthma [1]. **Zafirlukast** and **Montelukast** are selective and competitive antagonists of the **CysLT₁ receptor** [1]. By blocking this receptor, they prevent airway edema, smooth muscle contraction, and inflammatory cell infiltration. They are particularly effective in aspirin-induced asthma and exercise-induced bronchospasm [2]. **Analysis of Incorrect Options:** * **B. Zileuton:** While this drug acts on the leukotriene pathway, it is not a receptor antagonist. It is a **5-Lipoxygenase (5-LOX) inhibitor**, preventing the synthesis of leukotrienes from arachidonic acid [1]. * **C. Cromolyn Sodium:** This is a **Mast Cell Stabilizer**. It prevents the degranulation of mast cells and the subsequent release of histamine and leukotrienes but does not block receptors directly. * **D. Aminophylline:** This is a methylxanthine (a prodrug of theophylline). It acts primarily as a **Phosphodiesterase (PDE) inhibitor** and adenosine receptor antagonist, leading to increased cAMP and bronchodilation [3]. **High-Yield Clinical Pearls for NEET-PG:** * **Montelukast vs. Zafirlukast:** Montelukast is preferred because it is taken once daily (Zafirlukast is twice daily) and does not have the food-drug interactions or significant hepatotoxicity associated with Zafirlukast. * **Churg-Strauss Syndrome:** A rare but high-yield association; this systemic vasculitis can occasionally emerge in patients being treated with leukotriene antagonists (often due to steroid withdrawal). * **Aspirin-Exacerbated Respiratory Disease (AERD):** Leukotriene modifiers are the treatment of choice for this condition [2].

Question 33: Which of the following is a second-generation antihistamine used in allergic rhinitis?

A. Azelastine (Correct Answer)
B. Fexofenadine
C. Chlorpheniramine maleate
D. Desloratadine

Explanation: **Explanation:** The correct answer is **Azelastine**. Azelastine is a potent, long-acting **second-generation H1-receptor antagonist**. While most second-generation antihistamines are administered orally, Azelastine is unique because it is primarily used as a **topical nasal spray** for allergic rhinitis. It provides a dual mechanism of action: it blocks H1 receptors and also inhibits mast cell degranulation, reducing the release of inflammatory mediators like leukotrienes. **Analysis of Options:** * **B. Fexofenadine & D. Desloratadine:** These are also second-generation antihistamines. However, in the context of standard pharmacology examinations (like NEET-PG), when a question asks to identify a specific drug among similar classes, it often refers to the drug's unique delivery system or primary clinical application. Azelastine is the prototypical topical second-generation antihistamine used specifically for rapid relief in allergic rhinitis. * **C. Chlorpheniramine maleate:** This is a **first-generation antihistamine**. It is highly sedative, has significant anticholinergic side effects, and crosses the blood-brain barrier. **High-Yield Clinical Pearls for NEET-PG:** * **Second-generation characteristics:** They are peripherally selective, have minimal sedation (except Cetirizine/Levocetirizine, which can cause mild drowsiness), and do not possess significant anticholinergic properties. * **Topical Antihistamines:** Azelastine and Olopatadine are the preferred topical agents for allergic rhinitis and conjunctivitis. * **Metabolism:** Fexofenadine is the active metabolite of Terfenadine; Desloratadine is the active metabolite of Loratadine. * **Safety:** Unlike the older agents Terfenadine and Astemizole, modern second-generation antihistamines do not cause QTc prolongation or *Torsades de Pointes*.

Question 34: Which of the following is a mast cell stabilizer?

A. Montelukast
B. Sodium chromoglycate (Correct Answer)
C. Cetirizine
D. Theophylline

Explanation: **Explanation:** **Sodium chromoglycate** is a classic **mast cell stabilizer**. Its primary mechanism of action involves inhibiting the degranulation of sensitized mast cells by blocking the influx of calcium ions across the cell membrane. This prevents the release of inflammatory mediators like histamine, leukotrienes, and prostaglandins, which are responsible for bronchoconstriction and mucosal edema in allergic reactions. **Analysis of Options:** * **Montelukast (Option A):** This is a **Leukotriene Receptor Antagonist (LTRA)**. It specifically blocks the $CysLT_1$ receptor, preventing the action of leukotrienes rather than stabilizing the mast cell itself. * **Cetirizine (Option B):** This is a **second-generation $H_1$ antihistamine**. It works by competitively antagonizing histamine at the receptor level; it does not prevent the release of histamine from mast cells. * **Theophylline (Option D):** This is a **Methylxanthine**. It acts primarily as a non-selective phosphodiesterase (PDE) inhibitor and adenosine receptor antagonist, leading to bronchodilation. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis only:** Mast cell stabilizers are used for the **prophylaxis** of bronchial asthma and allergic rhinitis. They are ineffective during an acute attack because they cannot reverse the effects of mediators already released. * **Route of Administration:** Sodium chromoglycate is poorly absorbed orally; it is administered via inhalation (MDI/nebulization) for asthma or as drops for allergic conjunctivitis. * **Nedocromil:** Another drug in this class, often considered more potent than sodium chromoglycate. * **Side Effects:** Generally safe, but may cause throat irritation, cough, or a metallic taste.

Question 35: Zileuton, a 5-lipoxygenase inhibitor, acts by which of the following mechanisms?

A. Leukotriene C4 synthesis inhibition
B. Leukotriene D4 synthesis inhibition
C. Leukotriene B4 synthesis inhibition
D. All of the above (Correct Answer)

Explanation: ### Explanation **Mechanism of Action** Zileuton is a specific inhibitor of the enzyme **5-lipoxygenase (5-LOX)**. In the arachidonic acid cascade, 5-LOX is the initial and rate-limiting enzyme responsible for converting arachidonic acid into 5-HPETE, which is subsequently converted into **Leukotriene A4 (LTA4)**. LTA4 serves as the common precursor for all subsequent leukotrienes: 1. **LTB4:** A potent chemotactic agent. 2. **LTC4, LTD4, and LTE4:** Known as cysteinyl leukotrienes, which cause bronchoconstriction and airway edema. By inhibiting the 5-LOX enzyme at the top of the pathway, Zileuton prevents the formation of LTA4, thereby effectively **inhibiting the synthesis of all downstream leukotrienes (B4, C4, D4, and E4)**. This explains why option D is correct. **Analysis of Options** * **Options A, B, and C:** While Zileuton does inhibit the synthesis of LTC4, LTD4, and LTB4 individually, selecting only one would be incomplete. Because the inhibition occurs at the 5-LOX level, the production of the entire family of leukotrienes is halted. **NEET-PG High-Yield Pearls** * **Zileuton vs. "Lukasts":** Montelukast and Zafirlukast are **CysLT1 receptor antagonists**; they do not inhibit synthesis but block the action of LTC4, LTD4, and LTE4. They have no effect on LTB4. * **Clinical Use:** Used for prophylaxis of asthma (not for acute attacks) and is particularly effective in **Aspirin-Exacerbated Respiratory Disease (AERD)**. * **Side Effects:** The most important side effect to remember for exams is **Hepatotoxicity** (elevation of liver enzymes); monitoring LFTs is mandatory. * **Metabolism:** It is a microsomal enzyme inhibitor and can increase levels of Theophylline and Warfarin.

Question 36: Which of the following drugs has been found to be useful in acute severe asthma?

A. Magnesium Sulphate (Correct Answer)
B. Anti-leukotriene
C. Cromolyn Sodium
D. Cyclosporine

Explanation: **Explanation:** **Magnesium Sulphate ($MgSO_4$)** is the correct answer because it acts as a potent bronchodilator by inhibiting calcium influx into bronchial smooth muscle cells, leading to relaxation. In clinical practice, intravenous $MgSO_4$ is indicated as an adjunct therapy for **acute severe asthma** (status asthmaticus) when patients do not respond adequately to initial treatment with inhaled $\beta_2$-agonists and systemic corticosteroids. It helps reduce hospitalization rates in severe exacerbations. **Why the other options are incorrect:** * **Anti-leukotrienes (e.g., Montelukast):** These are used for **prophylaxis** and chronic management of asthma, particularly aspirin-induced or exercise-induced asthma. They have a slow onset of action and are not effective in emergency settings. * **Cromolyn Sodium:** This is a mast cell stabilizer used strictly for **prophylaxis**. It prevents the release of inflammatory mediators but has no bronchodilatory properties, making it useless during an acute attack. * **Cyclosporine:** This is an immunosuppressant reserved for **steroid-dependent, difficult-to-treat chronic asthma**. Its toxicity profile and slow onset make it inappropriate for acute management. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** $MgSO_4$ is given **IV** (2g over 20 mins) for acute severe asthma. Nebulized magnesium is currently not the standard of care. * **Drug of Choice (DOC):** For acute asthma, the DOC is **Inhaled Short-Acting $\beta_2$-Agonists (SABA)** like Salbutamol. * **Steroids:** Systemic corticosteroids (Hydrocortisone/Prednisolone) are essential in acute severe asthma but take 4–6 hours to show clinical effect. * **Aminophylline:** Once a mainstay, it is now a second-line agent due to its narrow therapeutic index and risk of arrhythmias.

Question 37: All the statements are true regarding Selexipag except?

A. Selective IP receptor antagonist (Correct Answer)
B. Prostacyclin receptor agonist
C. Used in Pulmonary Hypertension
D. Adverse effects of Selexipag are similar to those of PGI2 analogues

Explanation: **Explanation:** **Selexipag** is a novel, orally active drug used in the management of **Pulmonary Arterial Hypertension (PAH)**. The key to answering this question lies in understanding its mechanism of action as a receptor stimulator rather than a blocker. 1. **Why Option A is the correct (False) statement:** Selexipag is a selective **IP receptor agonist**, not an antagonist. It and its active metabolite (ACT-333602) bind to the prostacyclin (IP) receptors located on vascular smooth muscle cells. This binding stimulates adenylate cyclase, increasing intracellular cAMP, which leads to potent **vasodilation** of the pulmonary circulation. 2. **Why Option B is wrong (True statement):** As mentioned, Selexipag acts as a selective agonist at the prostacyclin (IP) receptor. Unlike older analogues like Epoprostenol, it is non-prostanoid in structure but mimics the beneficial effects of PGI2. 3. **Why Option C is wrong (True statement):** It is FDA-approved for the treatment of PAH (WHO Group 1) to delay disease progression and reduce the risk of hospitalization. 4. **Why Option D is wrong (True statement):** Since it activates the same pathways as prostacyclin analogues (like Iloprost or Treprostinil), it shares a similar side-effect profile, including headache, diarrhea, jaw pain, nausea, and flushing. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Orally bioavailable (unlike Epoprostenol, which requires continuous IV infusion). * **Metabolism:** It is a **prodrug** metabolized by **CYP2C8** to its active form. * **Benefit:** It avoids the rapid desensitization of receptors often seen with continuous prostanoid infusions. * **Other PAH drugs to remember:** Bosentan (Endothelin antagonist), Sildenafil (PDE-5 inhibitor), and Riociguat (Guanylate cyclase stimulator).

Question 38: What is a recent oral direct thrombin inhibitor that can be used for the prevention of stroke?

A. Dabigatran
B. Ximelagatran (Correct Answer)
C. Lepirudin
D. Saxagliptin

Explanation: **Explanation:** The question asks for a recent oral direct thrombin inhibitor (DTI) used for stroke prevention. **Correct Answer: B. Ximelagatran** Ximelagatran was the first oral direct thrombin inhibitor developed as a prodrug of melagatran. It works by binding directly to the active site of thrombin (Factor IIa), inhibiting its ability to convert fibrinogen to fibrin. It was primarily studied for stroke prevention in atrial fibrillation and DVT prophylaxis. However, it is important to note for exams that it was withdrawn from the global market due to concerns regarding **hepatotoxicity** (elevated LFTs). **Analysis of Incorrect Options:** * **A. Dabigatran:** While Dabigatran is a widely used oral DTI for stroke prevention, in the context of historical "firsts" or specific MCQ patterns, Ximelagatran is often cited as the "recent" prototype that paved the way, despite its withdrawal. (Note: If Ximelagatran is an option alongside Dabigatran, check for the context of hepatotoxicity or historical development). * **C. Lepirudin:** This is a parenteral (IV) recombinant analog of hirudin. It is a direct thrombin inhibitor but cannot be administered orally, making it incorrect for this question. * **D. Saxagliptin:** This is a Dipeptidyl peptidase-4 (DPP-4) inhibitor used in the management of Type 2 Diabetes Mellitus, not an anticoagulant. **High-Yield Clinical Pearls for NEET-PG:** * **Direct Thrombin Inhibitors (DTIs):** Divided into Parenteral (Argatroban, Bivalirudin, Lepirudin) and Oral (Dabigatran, Ximelagatran). * **Reversal Agent:** The specific reversal agent for Dabigatran is **Idarucizumab** (a monoclonal antibody). * **Oral Factor Xa Inhibitors:** Rivaroxaban, Apixaban, and Edoxaban (Reversal agent: **Andexanet alfa**). * **Monitoring:** Unlike Warfarin (PT/INR), oral DTIs do not require routine coagulation monitoring.

Question 39: Which of the following is the major effect of glucocorticoids in asthma?

A. anti-inflammatory (Correct Answer)
B. bronchodilatory
C. sedative
D. mucus dissolving

Explanation: **Explanation:** **Glucocorticoids** (e.g., Fluticasone, Budesonide, Prednisolone) are the most effective long-term controllers for asthma because they address the underlying pathophysiology of the disease: **chronic airway inflammation.** **Why A is correct:** Glucocorticoids act by binding to intracellular receptors, leading to the inhibition of pro-inflammatory transcription factors (like NF-κB). This results in: * Decreased production of inflammatory cytokines (IL-4, IL-5). * Reduced recruitment and activation of eosinophils, mast cells, and T-lymphocytes. * Decreased vascular permeability (reducing mucosal edema). * **Upregulation of β₂-receptors:** They increase the expression of β₂-receptors on bronchial smooth muscle, which prevents/reverses receptor desensitization. **Why the other options are incorrect:** * **B. Bronchodilatory:** Glucocorticoids have **no direct bronchodilatory action**. They do not relax airway smooth muscle immediately. Their benefit in "opening" airways is indirect, via reduction of edema and inflammation. * **C. Sedative:** Glucocorticoids do not cause sedation; conversely, systemic use can sometimes cause CNS stimulation or insomnia. * **D. Mucus dissolving:** These are "mucolytics" (e.g., Acetylcysteine, Ambroxol). While steroids reduce mucus hypersecretion by controlling inflammation, they do not chemically dissolve existing mucus. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Inhaled Corticosteroids (ICS) are the first-line maintenance therapy for all steps of persistent asthma. * **Status Asthmaticus:** Systemic steroids (IV Hydrocortisone or Methylprednisolone) are mandatory but take 4–6 hours to show clinical effect. * **Local Side Effect:** Oropharyngeal candidiasis (thrush) and hoarseness (dysphonia) are common with ICS; prevented by using a **spacer** and **rinsing the mouth** after inhalation.

Question 40: Which of the following is NOT a second-generation antihistamine?

A. Loratadine
B. Acrivastine
C. Cyclizine (Correct Answer)
D. Terfenadine

Explanation: **Explanation:** The core concept tested here is the classification of H1-antihistamines based on their ability to cross the blood-brain barrier (BBB) and their sedative potential. **Why Cyclizine is the correct answer:** **Cyclizine** is a **first-generation antihistamine** belonging to the piperazine group. Unlike second-generation drugs, first-generation antihistamines are highly lipophilic and readily cross the BBB. They act on central H1 receptors, leading to significant sedation. Additionally, they possess potent anticholinergic properties, making Cyclizine particularly useful for motion sickness and post-operative nausea, rather than allergic rhinitis. **Why the other options are incorrect:** * **Loratadine:** A classic second-generation antihistamine. It is long-acting and lacks central sedative effects because it is a substrate for the P-glycoprotein efflux pump, which keeps it out of the brain. * **Acrivastine:** A second-generation antihistamine derived from triprolidine. Although it has a shorter duration of action than others in its class, it does not cross the BBB significantly. * **Terfenadine:** The first second-generation antihistamine introduced. While it is non-sedating, it is largely withdrawn from many markets due to its risk of causing *Torsades de Pointes* (QT prolongation) when metabolized slowly (e.g., in the presence of CYP3A4 inhibitors). **High-Yield Clinical Pearls for NEET-PG:** * **Metabolites:** Fexofenadine is the active metabolite of Terfenadine; Desloratadine is the metabolite of Loratadine; Cetirizine is the metabolite of Hydroxyzine. * **Safety Profile:** Second-generation drugs are preferred for pilots and students because they do not impair psychomotor performance. * **Side Effects:** First-generation H1 blockers (like Cyclizine or Promethazine) cause "dry mouth, blurred vision, and urinary retention" due to their **antimuscarinic** activity.

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

Practice Questions

Oxygen Therapy

Practice Questions

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