Respiratory System Drugs — MCQs

Respiratory System Drugs Indian Medical PG Practice Questions and MCQs

Question 241: Which of the following drugs should be avoided in labouring women with bronchial asthma?

A. Ergometrine
B. Prostaglandin E1
C. Opioid analgesics
D. Prostaglandin F2α (Correct Answer)

Explanation: ***Prostaglandin F2α*** - **Prostaglandin F2α** (e.g., **carboprost**) is a potent **bronchoconstrictor** and can exacerbate asthma, leading to severe respiratory distress in susceptible individuals. - Its use for **uterine atony** in labouring women with a history of asthma is generally contraindicated due to the risk of inducing an **asthma attack**. *Ergometrine* - **Ergometrine** is an **ergot alkaloid** used to prevent or treat **postpartum hemorrhage** by causing sustained uterine contractions. - While it can cause some adverse effects like nausea or hypertension, it is **not generally contraindicated** in asthma and does not directly cause bronchoconstriction. *Prostaglandin E1* - **Prostaglandin E1** (e.g., **misoprostol**) is used for cervical ripening and induction of labour, or for preventing postpartum hemorrhage. - It generally has **bronchodilating** properties and is therefore considered safe for use in patients with asthma. *Opioid analgesics* - **Opioid analgesics** (e.g., **pethidine**, **morphine**) are commonly used for pain relief during labour. - While they can cause respiratory depression at high doses, they do **not directly induce bronchoconstriction** and are generally safe for use in asthmatic patients when carefully monitored.

Question 242: Which of the following is a centrally acting non-opioid antitussive?

A. Ambroxol
B. Guaifenesin
C. Diphenhydramine
D. Dextromethorphan (Correct Answer)

Explanation: ***Dextromethorphan*** - **Dextromethorphan** is a **centrally acting non-opioid antitussive** that suppresses the cough reflex by acting on the cough center in the medulla oblongata [1], [2]. - It is an **NMDA receptor antagonist** and a **sigma-1 receptor agonist**, which are the primary mechanisms responsible for its antitussive effects [2]. - Unlike opioid antitussives (codeine, hydrocodone), it does **not bind significantly to opioid receptors** at therapeutic doses and therefore lacks addiction potential, respiratory depression, and other opioid side effects [1], [3]. - It is a synthetic morphine analog (dextro-isomer) but is pharmacologically distinct from opioids [1]. *Ambroxol* - **Ambroxol** is a **mucolytic agent** that helps to thin and clear mucus from the respiratory tract. - It works by stimulating serous gland secretion and breaking down mucopolysaccharide fibers, which is different from suppressing the cough reflex centrally. *Guaifenesin* - **Guaifenesin** is an **expectorant** that increases the volume and reduces the viscosity of respiratory tract secretions. - This action helps to make coughs more productive, rather than directly suppressing the cough reflex. *Diphenhydramine* - **Diphenhydramine** is a first-generation **antihistamine** with significant sedative and anticholinergic properties. - While it has some antitussive effects, these are primarily due to its anticholinergic actions causing drying of respiratory secretions and its sedative properties, rather than direct central action on the cough center.

Question 243: Zileuton is:-

A. Phospholipase inhibitor
B. Leukotriene receptor antagonist
C. 5-Lipoxygenase inhibitor (Correct Answer)
D. Cyclooxygenase inhibitor

Explanation: ***5-Lipoxygenase inhibitor*** - **Zileuton** specifically inhibits **5-lipoxygenase**, an enzyme crucial for the synthesis of **leukotrienes**. - By blocking this enzyme, zileuton reduces the production of **pro-inflammatory leukotrienes**, which are involved in the pathophysiology of **asthma**. *Phospholipase inhibitor* - **Phospholipase A2 inhibitors** like **corticosteroids** act upstream by preventing the release of **arachidonic acid**, a precursor to both prostaglandins and leukotrienes. - Zileuton's action is more specific to the **leukotriene pathway**, occurring after arachidonic acid is already formed. *Cyclooxygenase inhibitor* - **Cyclooxygenase (COX) inhibitors** (like NSAIDs) block the synthesis of **prostaglandins** and **thromboxanes** from arachidonic acid. - Zileuton does not affect the COX pathway but rather targets the **lipoxygenase pathway**. *Leukotriene receptor antagonist* - **Leukotriene receptor antagonists** (e.g., Montelukast, Zafirlukast) block the binding of leukotrienes to their receptors, preventing their downstream effects. - While both target the **leukotriene pathway**, zileuton works by **inhibiting their production**, not their receptor binding.

Question 244: The non-sedative antihistamines are all EXCEPT one:

A. Cinnarizine (Correct Answer)
B. Fexofenadine
C. Levocetirizine
D. Desloratidine

Explanation: ***Cinnarizine*** - **Cinnarizine** is a first-generation antihistamine with notable **sedative effects** due to its ability to cross the blood-brain barrier. - It is primarily used for **motion sickness** and vestibular disorders, where its sedative properties can be a significant side effect. *Fexofenadine* - **Fexofenadine** is a second-generation antihistamine known for being **non-sedating**. - It has a high affinity for peripheral H1-receptors and does not readily cross the **blood-brain barrier**. *Levocetirizine* - **Levocetirizine** is the active enantiomer of cetirizine, also a **second-generation non-sedating** antihistamine. - It is effective in treating allergy symptoms with minimal central nervous system effects. *Desloratidine* - **Desloratidine** is the active metabolite of loratadine and is classified as a **non-sedating second-generation** antihistamine. - It has a long duration of action and low potential for causing drowsiness.

Question 245: H1 antihistaminic having best topical activity is:

A. Loratadine
B. Astemizole
C. Cetirizine
D. Azelastine (Correct Answer)

Explanation: **Azelastine (Correct Answer)** - **Azelastine** is an H1 antihistamine available as a **nasal spray** and **eye drops**, demonstrating excellent topical activity. - Its **lipophilicity** and local action make it highly effective for treating allergic rhinitis and conjunctivitis, with minimal systemic absorption. *Loratadine* - **Loratadine** is an oral, second-generation H1 antihistamine primarily used for systemic treatment of allergies. - It does not possess significant topical activity for local application in the nose or eyes. *Astemizole* - **Astemizole** is a second-generation H1 antihistamine that was withdrawn from the market due to significant **cardiac toxicity**, including QTc prolongation and torsades de pointes. - It was an oral medication and did not have widespread topical formulations. *Cetirizine* - **Cetirizine** is an oral H1 antihistamine known for its potency and relatively quick onset of action. - Although it can be used for systemic allergy relief, it is not primarily formulated or recognized for its topical efficacy compared to azelastine.

Question 246: All of the statements about H1 antihistamines are true except:

A. Tolerance may develop to some of its side effects
B. Many of them exhibit cholinergic effect (Correct Answer)
C. Local application can be used for contact dermatitis
D. Combination with an H2 antagonist may control some cases of chronic urticaria

Explanation: ***Many of them exhibit cholinergic effect*** - This statement is incorrect because many first-generation H1 antihistamines actually exert significant **anticholinergic effects**, which contribute to side effects like dry mouth, blurred vision, and urinary retention. - H1 antihistamines block **muscarinic acetylcholine receptors**, leading to diminished cholinergic activity, not increased cholinergic effects. *Tolerance may develop to some of its side effects* - Tolerance, particularly to the **sedative effects** of first-generation H1 antihistamines like diphenhydramine, is a well-documented phenomenon. - Patients may experience reduced drowsiness after repeated doses as their body adapts to the drug. *Local application can be used for contact dermatitis* - Topical H1 antihistamines like **diphenhydramine cream** can be used to alleviate the itching associated with localized allergic reactions such as contact dermatitis. - However, their topical use should be cautious due to the risk of **sensitization** and systemic absorption, especially over large areas or broken skin. *Combination with an H2 antagonist may control some cases of chronic urticaria* - Both histamine H1 and H2 receptors are involved in the pathophysiology of urticaria; H1 receptors mediate itch and flare, while H2 receptors modulate erythema and wheal formation. - Combining an **H1 antihistamine** with an **H2 antagonist** (e.g., ranitidine or cimetidine) can be more effective than H1 antagonists alone in reducing symptoms of chronic urticaria that are refractory to monotherapy, especially for severe cases.

Question 247: Which of the following is NOT a second generation antihistaminic ?

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

Explanation: **Cyclizine** - This is a **first-generation antihistamine** known for its significant sedative and anticholinergic effects, which distinguish it from second-generation drugs. - It readily crosses the **blood-brain barrier**, contributing to its central nervous system effects. *Loratadine* - This is a **second-generation antihistamine** characterized by its non-sedating properties. - It has a low affinity for **CNS histamine receptors**, reducing the likelihood of drowsiness. *Acrivastine* - This is also a **second-generation antihistamine** with a rapid onset of action and non-sedating properties. - Its chemical structure is related to triprolidine but it has a different metabolic profile. *Fexofenadine* - This is a **second-generation antihistamine** that is the active metabolite of terfenadine. - It is highly selective for **peripheral H1 receptors** and does not cross the blood-brain barrier, making it non-sedating.

Question 248: With which of the following receptors does theophylline have an antagonistic interaction?

A. Histamine receptors
B. Adenosine receptors (Correct Answer)
C. Imidazoline receptors
D. Bradykinin receptors

Explanation: ***Adenosine receptors*** - **Theophylline** acts as a **non-selective competitive antagonist** at **adenosine receptors** (A1, A2A, and A2B). - This antagonism contributes to its **bronchodilator effects** by blocking adenosine-induced bronchoconstriction and to its **stimulant effects** by enhancing neurotransmitter release. *Histamine receptors* - Theophylline does not primarily interact with **histamine receptors**. Its effects are mediated through different mechanisms. - While histamine plays a role in allergic reactions and airway smooth muscle contraction, theophylline's direct action is not on these receptors. *Imidazoline receptors* - Theophylline does not have a significant antagonistic interaction with **imidazoline receptors**. - These receptors are primarily involved in blood pressure regulation and sympathetic outflow, and are not a key target for theophylline's therapeutic effects. *Bradykinin receptors* - Theophylline does not directly antagonize **bradykinin receptors**. - Bradykinin is a potent vasodilator and inflammatory mediator, but its receptors are not the primary site of action for theophylline.

Question 249: A 60-year-old with COPD develops tremor after a medication. Which medication is most likely responsible?

A. Montelukast
B. Ipratropium
C. Fluticasone
D. Salmeterol (Correct Answer)

Explanation: ***Salmeterol*** - Salmeterol is a **long-acting beta-2 agonist (LABA)** commonly used in COPD [1]. Beta-2 agonists can cause **tremor** due to stimulation of skeletal muscle beta-2 receptors [2]. - This side effect is dose-dependent and more common with higher doses or in sensitive individuals. *Montelukast* - Montelukast is a **leukotriene receptor antagonist** used in asthma and allergic rhinitis, not typically a primary agent for COPD, and does not commonly cause tremor. - Its mechanism of action involves blocking leukotriene D4 receptors, which are not directly linked to muscle tremor. *Ipratropium* - Ipratropium is a **short-acting muscarinic antagonist (SAMA)** used in COPD. Its primary side effects are typically anticholinergic, such as dry mouth or blurred vision [3]. - Tremor is not a common or expected side effect of ipratropium as it does not act on beta-adrenergic receptors. *Fluticasone* - Fluticasone is an **inhaled corticosteroid (ICS)** used in COPD, often in combination with LABAs [1]. While systemic corticosteroids can cause tremor, the inhaled form has minimal systemic absorption. - **Inhaled corticosteroids** are primarily associated with local side effects like oral candidiasis or dysphonia.

Question 250: Adverse effects of salbutamol are all except

A. Tremors
B. Hypoglycemia (Correct Answer)
C. Hypokalemia
D. Tachycardia

Explanation: ***Hypoglycemia*** - Salbutamol, a **beta-2 adrenergic agonist**, is known to cause hyperglycemia by promoting glycogenolysis and gluconeogenesis, not hypoglycemia. - While it can indirectly affect insulin secretion, the predominant effect on glucose metabolism is an increase in blood sugar levels. *Tremors* - **Tremors**, particularly in the hands, are a very common adverse effect of salbutamol due to its non-selective stimulation of skeletal muscle beta-2 receptors. - This side effect is dose-dependent and often more noticeable with higher doses or systemic administration. *Hypokalemia* - Salbutamol can cause **hypokalemia** by promoting the intracellular shift of potassium, primarily through the activation of the Na+/K+-ATPase pump. - This effect is a significant concern, especially in patients with pre-existing cardiovascular conditions, as it can lead to cardiac arrhythmias. *Tachycardia* - **Tachycardia** is a common cardiovascular side effect of salbutamol, resulting from direct stimulation of cardiac beta-1 receptors (at higher doses or in sensitive individuals) and reflex tachycardia secondary to peripheral vasodilation. - Patients may experience palpitations or a noticeable increase in heart rate.

Practice by Chapter

Bronchodilators

Practice Questions

Corticosteroids in Respiratory Disorders

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Anti-inflammatory Respiratory Agents

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Mast Cell Stabilizers

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Leukotriene Modifiers

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Antitussives and Expectorants

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Nasal Decongestants

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Pulmonary Surfactants

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Drugs for Pulmonary Hypertension

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Oxygen Therapy

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