Respiratory System Drugs — MCQs

Respiratory System Drugs Indian Medical PG Practice Questions and MCQs

Question 161: A patient with a known history of COPD is being treated with theophylline. Which of the following side effects is commonly observed due to the drug's inhibition of phosphodiesterase 4 (PDE4)?

A. Headache (Correct Answer)
B. Diuresis
C. Cardiac arrhythmias
D. Epileptic seizures

Explanation: **Explanation:** Theophylline is a methylxanthine derivative used in COPD and asthma. It has a multi-modal mechanism of action: non-selective inhibition of **phosphodiesterase (PDE) enzymes** (increasing cAMP), antagonism of **adenosine receptors**, and enhancement of **histone deacetylation**. **1. Why Headache is Correct:** Theophylline inhibits **PDE4**, the primary PDE isoform in airway smooth muscle and inflammatory cells. However, PDE4 is also found in the central nervous system and vascular smooth muscle. Inhibition of PDE4 leads to an accumulation of cAMP, which causes **vasodilation of cerebral blood vessels**. This vasodilation is the primary trigger for the common side effect of **headaches**. **2. Analysis of Incorrect Options:** * **B. Diuresis:** This is primarily caused by the **antagonism of Adenosine A1 receptors** in the kidneys, which increases glomerular filtration and inhibits sodium reabsorption. * **C. Cardiac Arrhythmias:** These occur at high serum concentrations due to **Adenosine A1 receptor antagonism** (which increases heart rate) and inhibition of **PDE3** (which increases cardiac contractility and heart rate). * **D. Epileptic Seizures:** These are a sign of severe toxicity and are largely attributed to the **antagonism of Adenosine A1 receptors** in the brain, which removes the natural inhibitory effect of adenosine on neuronal firing. **Clinical Pearls for NEET-PG:** * **Therapeutic Window:** Narrow (10–20 µg/ml). Monitoring is essential. * **Metabolism:** Metabolized by **CYP1A2**. Enzyme inhibitors like Ciprofloxacin or Erythromycin can precipitate toxicity. * **PDE4 Specificity:** While Theophylline is non-selective, **Roflumilast** is a selective PDE4 inhibitor used in COPD, also frequently causing headache and weight loss.

Question 162: As a nasal decongestant, pseudoephedrine should be used cautiously in patients with which of the following conditions?

A. Hypertension
B. Hyperthyroidism
C. Ischemic heart disease
D. Urinary incontinence (Correct Answer)

Explanation: **Explanation:** **Mechanism of Action:** Pseudoephedrine is a sympathomimetic amine that acts as an agonist on both **$\alpha_1$ and $\beta$-adrenergic receptors**. Its primary use as a nasal decongestant stems from $\alpha_1$-mediated vasoconstriction of the nasal mucosa. **Why Urinary Incontinence is the Correct Answer:** The internal sphincter of the urinary bladder is rich in **$\alpha_1$-adrenergic receptors**. Stimulation of these receptors by pseudoephedrine causes **contraction of the internal sphincter** and increased urethral resistance. In patients with urinary incontinence (specifically overflow or associated with BPH), this can lead to **acute urinary retention**. Therefore, it must be used with extreme caution. (Note: While it may technically "improve" stress incontinence, it is a contraindication in patients prone to retention). **Analysis of Incorrect Options:** * **A, B, and C (Hypertension, Hyperthyroidism, Ischemic Heart Disease):** These are actually **standard contraindications/precautions** for pseudoephedrine due to its systemic sympathomimetic effects (tachycardia, increased peripheral resistance). However, in the context of this specific question (often sourced from standard textbooks like KD Tripathi), the focus is on the specific $\alpha_1$ effect on the bladder neck, which is a frequently tested "niche" side effect in PG exams. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For allergic rhinitis with congestion, intranasal corticosteroids are preferred over long-term decongestants. * **Rhinitis Medicamentosa:** Prolonged use (>3-5 days) of topical decongestants (like oxymetazoline) leads to rebound congestion; pseudoephedrine (oral) has a lower risk but higher systemic side effects. * **Precursor:** Pseudoephedrine is a precursor in the illicit manufacture of methamphetamine, leading to regulated sales in many regions. * **Mnemonic:** "Pseudoephedrine Pushes the Plug" (Constricts the bladder neck).

Question 163: Which of the following is not a bronchodilator?

A. Beta 2 agonists
B. Methylxanthines
C. Steroids (Correct Answer)
D. Anticholinergics

Explanation: **Explanation:** The core concept in respiratory pharmacology is distinguishing between **bronchodilators** (which provide symptomatic relief by relaxing airway smooth muscle) and **anti-inflammatory agents** (which treat the underlying disease process). **Why Steroids are the correct answer:** Corticosteroids (e.g., Fluticasone, Prednisolone) are **not bronchodilators**. They do not cause immediate relaxation of the airway smooth muscle. Instead, they act as **anti-inflammatory agents** by inhibiting the recruitment of inflammatory cells, reducing mucosal edema, and decreasing capillary permeability. Their primary role is "control" rather than "rescue," and they take several hours to days to show clinical effects. **Why the other options are incorrect:** * **Beta-2 Agonists (e.g., Salbutamol, Salmeterol):** These are the most potent bronchodilators. They stimulate $\beta_2$ receptors, increasing intracellular cAMP, which leads to direct relaxation of bronchial smooth muscle. * **Methylxanthines (e.g., Theophylline, Aminophylline):** These act by inhibiting the enzyme phosphodiesterase (PDE), preventing the breakdown of cAMP, and by antagonizing adenosine receptors, resulting in bronchodilation. * **Anticholinergics (e.g., Ipratropium, Tiotropium):** These block $M_3$ muscarinic receptors in the bronchial smooth muscle, inhibiting the bronchoconstrictor effect of acetylcholine. **High-Yield Clinical Pearls for NEET-PG:** * **Synergy:** While steroids aren't bronchodilators, they **upregulate $\beta_2$ receptors**, making the airways more responsive to $\beta_2$ agonists. * **Drug of Choice (DOC):** In acute asthma attacks, the DOC is a **SABA** (Short-Acting Beta Agonist). For chronic maintenance of persistent asthma, the DOC is **Inhaled Corticosteroids (ICS)**. * **Side Effect:** A common side effect of ICS is oropharyngeal candidiasis; patients should be advised to rinse their mouth after use.

Question 164: Long-term use of which of the following drugs is most likely associated with the development of tremors?

A. Propofol
B. Salbutamol (Correct Answer)
C. Betaxolol
D. Timolol

Explanation: **Explanation:** **Salbutamol** is a short-acting **Beta-2 ($\beta_2$) agonist** used primarily as a bronchodilator in asthma and COPD. The development of tremors is the most common dose-related side effect of $\beta_2$ agonists. This occurs because $\beta_2$ receptors are present on the **skeletal muscle fibers**. Stimulation of these receptors causes an increase in the speed of muscle contraction and an imbalance in muscle spindle activity, leading to fine muscle tremors (typically in the hands). **Analysis of Incorrect Options:** * **Propofol (A):** An intravenous anesthetic agent. While it can rarely cause excitatory phenomena (myoclonus) during induction, it is not associated with chronic tremors. * **Betaxolol (C) & Timolol (D):** These are **Beta-blockers**. Betaxolol is $\beta_1$-selective, while Timolol is non-selective. Beta-blockers are actually used clinically to *treat* tremors (e.g., essential tremors or physiological tremors) by blocking the $\beta_2$ receptors on skeletal muscles. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Tremor:** Direct stimulation of $\beta_2$ receptors on skeletal muscles (not a CNS effect). * **Other Side Effects of Salbutamol:** Hypokalemia (due to $K^+$ shift into cells), tachycardia (direct $\beta_2$ and reflex $\beta_1$ stimulation), and hyperglycemia. * **Tolerance:** Continuous use of $\beta_2$ agonists can lead to **downregulation (tachyphylaxis)** of receptors, though tremors often diminish over time as the body adapts. * **Drug of Choice:** Salbutamol remains the drug of choice for acute episodes of bronchospasm (Rescue inhaler).

Question 165: Dextromethorphan is an:

A. Antihistaminic
B. Antitussive (Correct Answer)
C. Expectorant
D. Antiallergic

Explanation: **Explanation:** **Dextromethorphan** is a synthetic derivative of morphine (specifically the d-isomer of the codeine analog levorphanol). Unlike other opioids, it lacks significant analgesic or addictive properties at standard doses. 1. **Why it is an Antitussive:** Dextromethorphan acts centrally by **elevating the cough threshold** in the medulla oblongata. It is a NMDA receptor antagonist and a sigma-1 receptor agonist. It is highly effective for the symptomatic relief of dry, non-productive coughs. Unlike codeine, it does not cause significant constipation or respiratory depression at therapeutic doses. 2. **Why the other options are incorrect:** * **Antihistaminic/Antiallergic (A & D):** While some first-generation antihistamines (like Diphenhydramine) are used in cough syrups for their sedative and anticholinergic effects, Dextromethorphan does not block histamine receptors. * **Expectorant (C):** Expectorants (e.g., Guaifenesin) work by increasing the volume and reducing the viscosity of airway secretions to help "clear" mucus. Dextromethorphan *suppresses* the cough reflex rather than facilitating the expulsion of mucus. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Central cough suppressant; NMDA receptor antagonist. * **Side Effects:** Dizziness, nausea, and drowsiness. In massive doses, it can cause hallucinations (dissociative state) and is sometimes abused ("Robo-tripping"). * **Drug Interaction:** It should **not** be given to patients on **MAO inhibitors**, as it can precipitate **Serotonin Syndrome** (hyperpyrexia, tremors, and hypertension). * **Contraindication:** It is generally avoided in children under 6 years and in patients with chronic bronchitis or asthma where cough suppression might lead to secretion retention.

Question 166: Which of the following is a long-acting sympathomimetic used in bronchial asthma?

A. Salbutamol
B. Terbutaline
C. Bambuterol
D. Salmeterol (Correct Answer)

Explanation: **Explanation:** The question tests the classification of $\beta_2$-agonists based on their duration of action. **1. Why Salmeterol is Correct:** Salmeterol is a **Long-Acting Beta-2 Agonist (LABA)**. It possesses a long, lipophilic side chain that anchors the molecule into the cell membrane near the $\beta_2$ receptor, allowing it to repeatedly engage the receptor. This results in a prolonged duration of action (**>12 hours**). LABAs are used for the maintenance treatment of asthma and COPD but are **not** used for acute relief due to their slow onset of action. **2. Why the Other Options are Incorrect:** * **Salbutamol (Albuterol) & Terbutaline:** These are **Short-Acting Beta-2 Agonists (SABA)**. They have a rapid onset (5–15 mins) but a short duration of action (2–6 hours). They are the "rescue medications" of choice for acute bronchospasm. * **Bambuterol:** While Bambuterol is a long-acting prodrug of terbutaline (taken once daily), it is technically a **prodrug** and not the primary sympathomimetic molecule itself. In the context of standard pharmacological classification for NEET-PG, Salmeterol and Formoterol are the prototypical LABAs. **3. High-Yield Clinical Pearls for NEET-PG:** * **Formoterol vs. Salmeterol:** Formoterol is a LABA with a **fast onset**, making it unique as it can be used for both maintenance and "SMART" therapy (Single Maintenance and Reliever Therapy). Salmeterol has a slow onset. * **Black Box Warning:** LABAs should **never** be used as monotherapy in asthma (increased risk of asthma-related deaths); they must always be combined with an Inhaled Corticosteroid (ICS). * **Ultra-LABAs:** Indacaterol, Vilanterol, and Olodaterol have a 24-hour duration, used primarily in COPD. * **Side Effects:** Muscle tremors (most common), tachycardia, and hypokalemia.

Question 167: A 50-year-old male, on anti-tuberculosis medication for two months, presents with hearing problems. Which of the following mechanisms of action is most likely responsible for these symptoms?

A. Binds to the 30S ribosome subunit and inhibits the initiation complex (Correct Answer)
B. Inhibits DNA-dependent RNA polymerase
C. Inhibits the synthesis of mycolic acid
D. Inhibits the synthesis of arabinoglycan subunits

Explanation: ### Explanation **Clinical Correlation:** The patient is presenting with ototoxicity (hearing problems) after starting anti-tuberculosis therapy (ATT). Among the first-line ATT drugs, **Streptomycin** is the only one known to cause vestibulocochlear nerve damage (Cranial Nerve VIII). Streptomycin is an **Aminoglycoside**. **Why Option A is Correct:** Aminoglycosides like Streptomycin exert their bactericidal action by crossing the bacterial cell membrane and irreversibly binding to the **30S ribosomal subunit**. This binding results in: 1. Interference with the formation of the **initiation complex**. 2. Misreading of the mRNA code. 3. Induction of premature termination of protein synthesis. **Why the Other Options are Incorrect:** * **Option B:** This is the mechanism of **Rifampicin**. While Rifampicin is a core component of ATT, its primary side effects are hepatotoxicity and orange discoloration of body fluids, not ototoxicity. * **Option C:** This is the mechanism of **Isoniazid (INH)**. INH is associated with peripheral neuropathy (prevented by Vitamin B6) and hepatotoxicity. * **Option D:** This is the mechanism of **Ethambutol**. Ethambutol inhibits arabinosyl transferase. Its classic side effect is **optic neuritis** (visual disturbances), not hearing loss. **High-Yield Clinical Pearls for NEET-PG:** * **Streptomycin** is the only first-line ATT drug given parenterally (IM) and the only one that is **not** hepatotoxic. * **Ototoxicity:** Streptomycin is more vestibulotoxic (balance) than cochleotoxic (hearing), but it can cause both. It is also nephrotoxic. * **Pregnancy:** Streptomycin is contraindicated in pregnancy as it can cause fetal ototoxicity (deafness). * **Mnemonic for Ethambutol:** **E**thambutol for **E**ye (Optic neuritis).

Question 168: What is the mode of action of Sodium Cromoglycate?

A. Mast cell stabilization (Correct Answer)
B. Antihistaminic
C. Anticholinergic
D. None of the above

Explanation: **Explanation:** **Correct Answer: A. Mast cell stabilization** **Mechanism of Action:** Sodium Cromoglycate is a **mast cell stabilizer**. It acts by inhibiting the degranulation of sensitized mast cells that occurs after exposure to specific antigens. It prevents the release of inflammatory mediators such as histamine, leukotrienes (LTs), and chemotactic factors. The molecular mechanism involves the **blockade of delayed chloride channels** in the mast cell membrane, which prevents the calcium influx necessary for degranulation. **Why other options are incorrect:** * **B. Antihistaminic:** Sodium Cromoglycate does not block histamine receptors (H1 or H2) nor does it antagonize the effects of histamine once released. It only prevents histamine from being released in the first place. * **C. Anticholinergic:** It has no effect on muscarinic receptors. Anticholinergic drugs (like Ipratropium bromide) work by blocking M3 receptors to cause bronchodilation, whereas Cromoglycate is a prophylactic agent with no direct bronchodilatory action. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis Only:** It is ineffective in treating an acute attack of asthma (not a bronchodilator). It is used for the long-term prevention of bronchial asthma and exercise-induced bronchospasm. * **Route:** It is poorly absorbed orally; hence, it is administered via inhalation (as a fine powder or aerosol). * **Other Uses:** It is used topically for allergic rhinitis (nasal spray) and allergic conjunctivitis (eye drops). * **Nedocromil:** A related drug that is more potent and can also inhibit inflammatory cells like eosinophils and monocytes.

Question 169: All of the following statements about leukotriene modifiers in the management of bronchial asthma are true EXCEPT?

A. May be used for acute asthma (Correct Answer)
B. May be used for exercise-induced asthma
C. Zileuton is a leukotriene modifier
D. May uncover Churg-Strauss syndrome

Explanation: **Explanation** Leukotriene modifiers (LTRA) are essential maintenance therapies in asthma, but they have specific clinical limitations and associations that are frequently tested in NEET-PG. **1. Why Option A is the Correct Answer (The "Except" Statement):** Leukotriene modifiers (e.g., Montelukast, Zafirlukast) are **not indicated for acute asthma attacks**. They have a slow onset of action and are significantly less effective than inhaled $\beta_2$-agonists (SABA) for rapid bronchodilation. Their role is strictly limited to **prophylaxis** and chronic management of persistent asthma. **2. Analysis of Other Options:** * **Option B (Exercise-induced asthma):** LTRAs are effective in preventing exercise-induced bronchoconstriction. They are often preferred in pediatric patients or those who wish to avoid frequent inhaler use before physical activity. * **Option C (Zileuton):** This is a 5-lipoxygenase (5-LOX) inhibitor that prevents the synthesis of leukotrienes ($LTB_4, LTC_4, LTD_4, LTE_4$). While Montelukast blocks the receptor ($CysLT_1$), Zileuton is indeed classified as a leukotriene modifier. * **Option D (Churg-Strauss Syndrome):** The use of LTRAs (especially during corticosteroid tapering) is associated with the unmasking of **Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss Syndrome)**. This presents as eosinophilia, vasculitic rash, and pulmonary infiltrates. **Clinical Pearls for NEET-PG:** * **Aspirin-Induced Asthma:** LTRAs are the **drugs of choice** for Aspirin-Exacerbated Respiratory Disease (AERD). * **Metabolism:** Zafirlukast and Zileuton inhibit Cytochrome P450 enzymes (CYP3A4/1A2), potentially increasing Warfarin levels. **Montelukast** does not have these significant drug interactions. * **Neuropsychiatric effects:** The FDA has issued a boxed warning for Montelukast regarding serious mental health side effects (agitation, aggression, suicidal ideation).

Question 170: Omalizumab is used for which of the following conditions?

A. Ulcerative colitis
B. Crohn disease
C. Asthma (Correct Answer)
D. Psoriatic arthritis

Explanation: **Explanation:** **Omalizumab** is a recombinant DNA-derived humanized monoclonal antibody specifically designed to target **Immunoglobulin E (IgE)**. **Why Asthma is correct:** The underlying mechanism of Omalizumab involves binding to the Fc portion of free circulating IgE. This prevents IgE from binding to its high-affinity receptors (FcεRI) on the surface of mast cells and basophils. By limiting the cross-linking of IgE, it inhibits the release of inflammatory mediators (like histamine and leukotrienes) that trigger an asthma attack. It is clinically indicated for **moderate-to-severe persistent allergic asthma** in patients who are inadequately controlled with inhaled corticosteroids. **Why other options are incorrect:** * **Ulcerative Colitis & Crohn’s Disease:** These are Inflammatory Bowel Diseases (IBD) primarily managed with TNF-alpha inhibitors (e.g., Infliximab, Adalimumab) or anti-integrin antibodies (e.g., Vedolizumab), not anti-IgE therapy. * **Psoriatic Arthritis:** This condition is typically treated with DMARDs or biologics targeting TNF-alpha, IL-17 (e.g., Secukinumab), or IL-12/23 (e.g., Ustekinumab). **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Administered via **subcutaneous injection** every 2–4 weeks. * **Other Indications:** Also FDA-approved for **Chronic Spontaneous Urticaria (CSU)** and nasal polyps. * **Key Side Effect:** The most serious (though rare) side effect is **anaphylaxis**; patients should be monitored post-injection. * **Selection Criteria:** Before starting Omalizumab, a patient's **total serum IgE levels** must be measured to determine the appropriate dosage.

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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