Respiratory System Drugs — MCQs

Respiratory System Drugs Indian Medical PG Practice Questions and MCQs

Question 121: What is the loading dose of aminophylline?

A. 50–75 mg/kg
B. 0.5–1 mg/kg
C. 2–3.5 mg/kg
D. 5–6 mg/kg (Correct Answer)

Explanation: **Explanation:** **Aminophylline** is a methylxanthine derivative (a salt of theophylline and ethylenediamine) used as a bronchodilator in the management of acute severe asthma and COPD. **Why 5–6 mg/kg is correct:** The goal of a loading dose is to rapidly achieve a therapeutic plasma concentration (usually 10–20 µg/ml). Aminophylline has a relatively narrow therapeutic index. A loading dose of **5–6 mg/kg** (administered intravenously over 20–30 minutes) is standard for patients who have not previously been taking theophylline. This dose is calculated based on **ideal body weight** to avoid toxicity, as the drug does not distribute significantly into body fat. **Analysis of Incorrect Options:** * **A (50–75 mg/kg):** This is a massive overdose. Such levels would lead to severe toxicity, including intractable seizures and fatal cardiac arrhythmias. * **B (0.5–1 mg/kg):** This dose is sub-therapeutic and would fail to achieve the necessary plasma concentration to relieve bronchospasm. * **C (2–3.5 mg/kg):** While closer, this is generally considered the "half-loading dose" used only if the patient has already been taking oral theophylline, to prevent toxicity while still boosting levels. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Aminophylline contains approximately **80% theophylline**. If switching from IV aminophylline to oral theophylline, the dose must be adjusted. * **Metabolism:** It follows **First-order kinetics** at therapeutic levels but can shift to **Zero-order kinetics** (saturation) at higher doses, leading to rapid toxicity. * **Drug Interactions:** Metabolism is **increased** (requiring higher doses) by enzyme inducers like **Rifampicin and Smoking**. Metabolism is **decreased** (requiring lower doses) by enzyme inhibitors like **Erythromycin and Ciprofloxacin**. * **Side Effects:** Tachycardia, palpitations, and gastric irritation are common; seizures are the most serious sign of toxicity.

Question 122: What is true about zafirlukast?

A. It inhibits lipoxygenase
B. It blocks the LT receptor
C. It can be administered orally
D. All of the above (Correct Answer)

Explanation: **Explanation:** Zafirlukast is a key drug in the management of bronchial asthma, belonging to the class of **Leukotriene Modifiers**. **1. Why Option D is correct:** Zafirlukast acts primarily as a **selective and competitive antagonist at the CysLT1 receptor** (Cysteinyl Leukotriene receptor). By blocking this receptor, it prevents the actions of LTC4, LTD4, and LTE4, which are potent mediators of bronchoconstriction, airway edema, and mucus secretion. While its primary mechanism is receptor blockade, pharmacological studies indicate that zafirlukast also exerts an **inhibitory effect on the 5-Lipoxygenase (5-LOX) enzyme pathway** indirectly or at higher concentrations, reducing the overall synthesis of leukotrienes. Furthermore, unlike many older asthma medications, zafirlukast is highly effective when **administered orally**, making it a preferred choice for long-term prophylaxis. **2. Breakdown of Options:** * **Option A:** It inhibits the leukotriene pathway (though Zileuton is the classic direct 5-LOX inhibitor, Zafirlukast shares inhibitory properties on the pathway). * **Option B:** This is its primary mechanism of action (CysLT1 receptor antagonism). * **Option C:** It is well-absorbed via the GI tract, though its absorption is decreased by food. **3. High-Yield Clinical Pearls for NEET-PG:** * **Indications:** Used for **prophylaxis** of chronic asthma and Aspirin-Induced Asthma (AIA). It is *not* used for acute attacks. * **Drug Interactions:** Zafirlukast is a **CYP2C9 and CYP3A4 inhibitor**. It can significantly increase the serum levels of **Warfarin**, leading to increased prothrombin time (bleeding risk). * **Adverse Effects:** Rare but serious association with **Churg-Strauss Syndrome** (eosinophilic granulomatosis with polyangiitis) and potential hepatotoxicity. * **Comparison:** Unlike Montelukast (taken once daily), Zafirlukast is typically taken **twice daily** and must be taken on an empty stomach.

Question 123: What is the most common side effect of inhaled corticosteroids?

A. Pneumonia
B. Oropharyngeal candidiasis (Correct Answer)
C. Atrophic rhinitis
D. Pituitary adrenal suppression

Explanation: **Explanation:** **Inhaled Corticosteroids (ICS)**, such as Budesonide and Fluticasone, are the mainstay of treatment for chronic bronchial asthma [1]. **Why Oropharyngeal Candidiasis is the correct answer:** The most common side effect of ICS is **Oropharyngeal Candidiasis (Oral Thrush)**. This occurs because the steroid particles deposit on the oral mucosa, leading to local immunosuppression. This allows the opportunistic fungus *Candida albicans* to proliferate. Another very common local side effect is **Hoarseness of voice (Dysphonia)**, caused by myopathy of the laryngeal muscles. [1] **Analysis of Incorrect Options:** * **A. Pneumonia:** While long-term use of high-dose ICS (especially Fluticasone) is associated with an increased risk of pneumonia in COPD patients, it is not as common as local oral complications. * **C. Atrophic rhinitis:** This is a chronic inflammation of the nose characterized by mucosal atrophy; it is not a recognized side effect of inhaled or intranasal steroids. * **D. Pituitary adrenal suppression:** This is a systemic side effect. While ICS are designed to have low systemic bioavailability, adrenal suppression only occurs with very high doses over prolonged periods [1]. It is much less common than local side effects. **NEET-PG High-Yield Pearls:** * **Prevention:** To minimize the risk of oral thrush and dysphonia, patients should be advised to **rinse their mouth with water and spit** [1] after every use. * **Device Optimization:** Using a **spacer device** reduces oropharyngeal deposition and increases lung delivery, further decreasing the risk of local side effects [1]. * **First-pass metabolism:** Most ICS have high first-pass metabolism, which limits systemic toxicity if the swallowed portion is absorbed from the gut [1].

Question 124: Which of the following is an adverse effect of 2 agonists?

A. Hypoglycemia
B. Hypomagnesemia
C. Hypophosphatemia
D. Hypokalemia (Correct Answer)

Explanation: ### Explanation **Mechanism of Action for Hypokalemia:** $\beta_2$ agonists (like Salbutamol or Terbutaline) stimulate $\beta_2$ receptors, which activates the **Na⁺/K⁺-ATPase pump** located on the cell membranes of skeletal muscles and the liver. This activation causes an influx of potassium ions from the extracellular fluid (plasma) into the intracellular compartment. This shift results in a decrease in serum potassium levels (**Hypokalemia**). This effect is dose-dependent and is often utilized therapeutically in the emergency management of hyperkalemia. **Analysis of Incorrect Options:** * **A. Hypoglycemia:** Incorrect. $\beta_2$ stimulation actually promotes glycogenolysis in the liver and skeletal muscle, leading to **hyperglycemia**, not hypoglycemia. * **B. Hypomagnesemia:** While $\beta_2$ agonists can cause a mild decrease in magnesium, it is not the classic or most frequently tested metabolic side effect compared to hypokalemia. * **C. Hypophosphatemia:** While intracellular shifts can occasionally affect phosphate, it is not a primary or characteristic adverse effect of $\beta_2$ agonists. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolic Effects:** $\beta_2$ agonists cause "Hypo-K" (Hypokalemia) and "Hyper-G" (Hyperglycemia). * **Cardiac Effects:** They cause tachycardia (via direct $\beta_2$ stimulation on the heart and reflex tachycardia due to peripheral vasodilation). * **Muscle Effects:** Fine skeletal muscle **tremors** are the most common side effect (due to $\beta_2$ receptors on the muscle spindles). * **Tolerance:** Prolonged use leads to **downregulation (tachyphylaxis)** of $\beta_2$ receptors, which can be prevented by co-administration of corticosteroids.

Question 125: A 34-year-old man with a long history of asthma is referred to a pulmonologist. The physician decides to prescribe zileuton. What is the mechanism of action of zileuton?

A. Antagonize leukotriene D4 receptor
B. Inhibit 5-lipoxygenase (Correct Answer)
C. Inhibit phosphodiesterases
D. Stimulate beta2 receptors

Explanation: ### Explanation **Correct Option: B. Inhibit 5-lipoxygenase** Zileuton is a specific inhibitor of **5-lipoxygenase (5-LOX)**, the key enzyme responsible for converting arachidonic acid into leukotrienes (LTB4, LTC4, LTD4, and LTE4). By inhibiting this enzyme, zileuton prevents the synthesis of all leukotrienes. In asthma, leukotrienes are potent mediators that cause bronchoconstriction, increased mucus secretion, and airway edema. By blocking their production, zileuton helps in the prophylactic management of chronic asthma. **Analysis of Incorrect Options:** * **Option A (Antagonize LTD4 receptor):** This is the mechanism of **Montelukast** and **Zafirlukast**. These drugs block the CysLT1 receptor rather than inhibiting the synthesis of leukotrienes. * **Option C (Inhibit phosphodiesterases):** This is the mechanism of **Theophylline** (non-selective PDE inhibitor) and **Roflumilast** (PDE-4 inhibitor). These drugs increase cAMP levels to cause bronchodilation. * **Option D (Stimulate beta2 receptors):** This describes **Beta-agonists** like Salbutamol (SABA) or Salmeterol (LABA), which act via Gs-protein coupled receptors to relax bronchial smooth muscle. **High-Yield Clinical Pearls for NEET-PG:** * **Hepatotoxicity:** Zileuton is associated with an elevation in liver enzymes; therefore, periodic **LFT monitoring** is mandatory. * **Metabolism:** It is a microsomal enzyme inhibitor and can increase the plasma levels of **Theophylline** and **Warfarin**. * **Aspirin-Exacerbated Respiratory Disease (AERD):** Leukotriene modifiers (both 5-LOX inhibitors and receptor antagonists) are particularly effective in patients with "Aspirin Triad" (Asthma, Nasal polyps, and Aspirin sensitivity). * **Route:** Unlike many asthma drugs, Zileuton is administered **orally**.

Question 126: Relatively higher dose of theophylline is required to attain therapeutic plasma concentration in:

A. Smokers (Correct Answer)
B. Congestive heart failure patients
C. Those receiving erythromycin
D. Those receiving cimetidine

Explanation: **Explanation:** Theophylline is a methylxanthine with a narrow therapeutic index (10–20 µg/ml). It is primarily metabolized in the liver by the **Cytochrome P450 (CYP1A2)** enzyme system. **Why Smokers require a higher dose:** Cigarette smoking (and marijuana) introduces polycyclic aromatic hydrocarbons, which act as **potent enzyme inducers** of CYP1A2. This increases the metabolic clearance of theophylline, shortening its half-life. Consequently, smokers require a **higher dose** (often 50-100% more) to maintain therapeutic plasma concentrations compared to non-smokers. **Analysis of Incorrect Options:** * **Congestive Heart Failure (CHF):** CHF causes hepatic congestion and reduced blood flow to the liver, which **decreases** theophylline clearance. These patients require a *lower* dose to avoid toxicity. * **Erythromycin:** This is a known **enzyme inhibitor**. It inhibits the CYP system, leading to decreased metabolism and increased plasma levels of theophylline. A *lower* dose is required. * **Cimetidine:** Similar to erythromycin, cimetidine is a classic **enzyme inhibitor** that reduces theophylline clearance, necessitating a *lower* dose. **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Inducers (Need higher dose):** Smoking, Phenytoin, Rifampicin, Phenobarbitone, Carbamazepine. * **Enzyme Inhibitors (Need lower dose):** Cimetidine, Erythromycin (Macrolides), Ciprofloxacin (Fluoroquinolones), Allopurinol. * **Toxicity:** Early signs include anorexia, nausea, and vomiting. Severe toxicity leads to **cardiac arrhythmias** and **seizures**. * **Mechanism:** Non-selective phosphodiesterase (PDE) inhibition and adenosine receptor antagonism.

Question 127: What is the most common side effect of short-acting beta-2 agonists used in asthma?

A. Muscle tremors (Correct Answer)
B. Hypokalemia
C. Hypoglycemic attacks
D. Sedation

Explanation: **Explanation:** Short-acting beta-2 agonists (SABA), such as Salbutamol (Albuterol), are the mainstay for acute asthma relief. **1. Why Muscle Tremors are the most common side effect:** Beta-2 receptors are not only located in the bronchial smooth muscle but are also found on the **skeletal muscles**. Stimulation of these receptors causes an increase in the speed of muscle contraction and a shift in the muscle spindle sensitivity, leading to fine muscle tremors (particularly in the hands). This is the **most frequent** dose-limiting side effect of systemic or high-dose inhaled therapy. **2. Analysis of Incorrect Options:** * **B. Hypokalemia:** While SABAs do cause hypokalemia (by stimulating the Na+/K+ ATPase pump, shifting potassium into cells), it is less common than tremors at standard doses. Clinically, this effect is actually utilized to treat hyperkalemia. * **C. Hypoglycemic attacks:** Beta-2 agonists actually cause **hyperglycemia** (not hypoglycemia) by stimulating glycogenolysis in the liver and skeletal muscle. * **D. Sedation:** SABAs often cause CNS stimulation, leading to nervousness, anxiety, and restlessness, rather than sedation. **NEET-PG High-Yield Pearls:** * **Tolerance:** Continuous use of SABAs can lead to the "downregulation" of beta-receptors (tachyphylaxis). * **Cardiac Effects:** At high doses, SABAs lose selectivity and stimulate Beta-1 receptors, causing **tachycardia** and palpitations. * **Drug of Choice:** Salbutamol is the DOC for acute bronchospasm; Salmeterol/Formoterol (LABAs) are used for maintenance but *never* as monotherapy in asthma.

Question 128: A child was given a leukotriene receptor antagonist for prophylaxis of asthma. Which of the following drugs is a leukotriene receptor antagonist?

A. Montelukast (Correct Answer)
B. Zileuton
C. Nedocromil
D. Verapamil

Explanation: ### Explanation **Correct Option: A (Montelukast)** Leukotrienes (specifically $LTC_4$, $LTD_4$, and $LTE_4$) are potent bronchoconstrictors and mediators of inflammation in asthma. **Montelukast** and **Zafirlukast** are selective and competitive **CysLT₁ receptor antagonists**. By blocking these receptors on bronchial smooth muscle, they prevent bronchoconstriction, airway edema, and mucus secretion. They are primarily used for the **prophylaxis** of bronchial asthma and are particularly effective in **aspirin-induced asthma** and exercise-induced bronchospasm. **Analysis of Incorrect Options:** * **B. Zileuton:** While this drug affects the leukotriene pathway, it is a **5-Lipoxygenase (5-LOX) inhibitor**, not a receptor antagonist. It prevents the synthesis of leukotrienes from arachidonic acid. * **C. Nedocromil:** This is a **Mast Cell Stabilizer** (similar to Sodium Cromoglycate). It prevents the degranulation of mast cells and the release of inflammatory mediators like histamine but does not act directly on leukotriene receptors. * **D. Verapamil:** This is a **Phenylalkylamine Calcium Channel Blocker (CCB)** used primarily for hypertension, angina, and supraventricular arrhythmias. It has no therapeutic role in asthma management. **High-Yield NEET-PG Pearls:** * **Churg-Strauss Syndrome:** A rare but high-yield side effect associated with the use of leukotriene antagonists (Montelukast/Zafirlukast) is the unmasking of systemic vasculitis. * **Neuropsychiatric Events:** The FDA has issued a boxed warning for Montelukast regarding serious mental health side effects (e.g., agitation, aggression, suicidal ideation). * **Route:** Montelukast is administered **orally**, making it a preferred choice for pediatric patients who struggle with inhaler techniques.

Question 129: A 29-year-old woman presents with increasing shortness of breath and coughing. She had asthma as a child but has not required any treatment for the past 10 years. On examination, she has expiratory wheezes. For the above patient, select the most appropriate medication to cause bronchodilation.

A. albuterol (Correct Answer)
B. ethanol
C. amitriptyline
D. NSAIDs

Explanation: ### Explanation **Correct Option: A. Albuterol** The patient is presenting with an acute exacerbation of asthma, characterized by shortness of breath and expiratory wheezes. The primary goal in acute management is to reverse bronchoconstriction. **Albuterol** is a **Short-Acting Beta-2 Agonist (SABA)**. It works by stimulating $\beta_2$ receptors on bronchial smooth muscle, leading to an increase in intracellular cAMP, which results in rapid smooth muscle relaxation and bronchodilation. It is the "rescue" drug of choice for acute symptoms. **Analysis of Incorrect Options:** * **B. Ethanol:** Alcohol has no role in bronchodilation. In some patients, it may even trigger asthma symptoms due to histamine release or sulfite preservatives. * **C. Amitriptyline:** This is a Tricyclic Antidepressant (TCA). It possesses significant **anticholinergic** side effects (like dry mouth), but it is not used for respiratory therapy. Furthermore, TCAs can occasionally worsen respiratory depression in overdose. * **D. NSAIDs:** Non-Steroidal Anti-inflammatory Drugs (like Aspirin) are generally **contraindicated** or used with caution in asthmatics. They can shift arachidonic acid metabolism toward the leukotriene pathway, potentially triggering **Aspirin-Exacerbated Respiratory Disease (AERD)** or "Samter’s Triad." **Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** SABAs (Albuterol/Salbutamol) are the DOC for acute asthma attacks. * **Mechanism:** $\beta_2$ agonists $\rightarrow$ $\uparrow$ Adenyl Cyclase $\rightarrow$ $\uparrow$ cAMP $\rightarrow$ Bronchodilation. * **Side Effects:** Tremors (most common, due to $\beta_2$ stimulation in skeletal muscle), tachycardia, and hypokalemia. * **Samter’s Triad:** Asthma, Aspirin sensitivity, and Nasal polyps. * **Maintenance:** Inhaled Corticosteroids (ICS) are the mainstay for long-term control (e.g., Fluticasone, Budesonide).

Question 130: All adverse effects of theophylline are mediated by adenosine A1 receptor antagonism, except:

A. Cardiac arrhythmias
B. Diuresis
C. Seizures
D. Gastrointestinal discomfort (Correct Answer)

Explanation: **Explanation:** Theophylline, a methylxanthine used in asthma and COPD, has a narrow therapeutic index and acts via two primary mechanisms: **non-selective phosphodiesterase (PDE) inhibition** (increasing cAMP) and **adenosine receptor antagonism**. **1. Why Gastrointestinal (GI) discomfort is the correct answer:** GI side effects, such as nausea, vomiting, and abdominal pain, are primarily mediated by **PDE inhibition** and direct local irritation of the gastric mucosa. Unlike the other options, these effects are not linked to adenosine receptor blockade. **2. Analysis of Incorrect Options (Adenosine-mediated effects):** Adenosine normally acts as an inhibitory neuromodulator in the body. By antagonizing adenosine receptors (specifically A1 and A2), theophylline causes: * **Cardiac Arrhythmias (A):** Adenosine normally slows the heart rate (negative chronotropy/dromotropy). Antagonism leads to tachycardia and arrhythmias. * **Diuresis (B):** Adenosine causes afferent arteriolar constriction in the kidney. Antagonizing this leads to vasodilation, increased renal blood flow, and diuresis. * **Seizures (C):** Adenosine is a potent CNS depressant. Antagonism at A1 receptors in the brain leads to CNS excitation, lowering the seizure threshold. **Clinical Pearls for NEET-PG:** * **Therapeutic Range:** 10–20 µg/mL. Toxicity often starts >20 µg/mL. * **Metabolism:** It follows **zero-order kinetics** in overdose. * **Drug Interactions:** Enzyme inhibitors (Cimetidine, Erythromycin, Ciprofloxacin) increase theophylline levels, while enzyme inducers (Rifampicin, Phenytoin, Smoking) decrease them. * **DOC for Toxicity:** Activated charcoal (multiple doses) or Hemoperfusion in severe cases.

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

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Drugs for Pulmonary Hypertension

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Oxygen Therapy

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