Bronchodilators — MCQs
Aminophylline inhibits which of the following enzymes?
The activation of muscarinic receptors in bronchiolar smooth muscle is associated with:
Which of the following is NOT a beta-2 agonist?
All of the following drugs are used for the treatment of urinary incontinence except:
Which of the following antimicrobials should not be given to a chronic asthmatic patient managed on theophylline therapy?
What is a contraindication of antimuscarinic drugs?
Maximum effect of bronchodilatation in asthma is caused by -
Tamsulosin belongs to
Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)
What is an atypical side effect of montelukast?
Bronchodilators Indian Medical PG Practice Questions and MCQs
Question 1: Aminophylline inhibits which of the following enzymes?
- A. MAO
- B. Alcohol dehydrogenase
- C. Cytochrome P450
- D. Phosphodiesterase (Correct Answer)
Explanation: ***Phosphodiesterase*** - **Aminophylline** is a methylxanthine derivative that primarily acts as a **phosphodiesterase (PDE) inhibitor** [1], [2]. - By inhibiting PDE, aminophylline increases intracellular levels of **cAMP** and **cGMP**, leading to **bronchodilation** and other effects [2], [3]. *MAO* - **MAO (monoamine oxidase)** inhibitors are antidepressants that prevent the breakdown of neurotransmitters like serotonin, norepinephrine, and dopamine. - Aminophylline does not significantly inhibit MAO. *Alcohol dehydrogenase* - **Alcohol dehydrogenase** is an enzyme responsible for metabolizing alcohol (ethanol) in the liver. - Aminophylline has no direct inhibitory effect on alcohol dehydrogenase. *Cytochrome P450* - **Cytochrome P450 (CYP450)** enzymes are a group of enzymes primarily involved in the metabolism of drugs and other xenobiotics in the liver [4]. - While aminophylline (and its active metabolite theophylline) can be metabolized by and *affect* certain **CYP450** isoenzymes (e.g., CYP1A2), it does not act as a general inhibitor of the entire CYP450 system; its primary therapeutic action is not through CYP450 inhibition.
Question 2: The activation of muscarinic receptors in bronchiolar smooth muscle is associated with:
- A. Increase in IP3 and DAG (Correct Answer)
- B. Inhibition of protein kinase C
- C. Activation of adenylyl cyclase
- D. Opening of Na+/K+ cation channels
Explanation: ***Increase in IP3 and DAG*** - **Muscarinic receptors** on bronchial smooth muscle (M3 receptors) are **Gq protein-coupled receptors** [1]. - Activation of **Gq proteins** leads to the activation of **phospholipase C**, which hydrolyzes **PIP2** into **IP3** and **DAG** [1, 3]. *Inhibition of protein kinase C* - **DAG** (diacylglycerol), produced from the breakdown of PIP2, **activates protein kinase C (PKC)**, rather than inhibiting it [2]. - This activation of PKC contributes to downstream cellular responses, including smooth muscle contraction [1]. *Activation of adenylyl cyclase* - **Adenylyl cyclase** is typically activated by **Gs protein-coupled receptors**, leading to an increase in **cAMP**. - **Muscarinic (M3) receptors** are **Gq-coupled**, so they do not activate adenylyl cyclase; instead, they operate through the phospholipase C pathway [1, 3]. *Opening of Na+/K+ cation channels* - While some neurotransmitter receptors are **ligand-gated ion channels** (e.g., nicotinic receptors), muscarinic receptors are **G protein-coupled receptors** [1]. - Their activation does not directly lead to the opening of **Na+/K+ cation channels**; rather, they initiate intracellular signaling cascades.
Question 3: Which of the following is NOT a beta-2 agonist?
- A. Ketotifen (Correct Answer)
- B. Terbutaline
- C. Salbutamol
- D. Bambuterol
Explanation: ***Ketotifen*** - **Ketotifen** is an **oral anti-allergic drug** that acts as a **mast cell stabilizer** and **H1-antihistamine**, not a beta-2 agonist. - It is used for **prophylactic treatment** of asthma and allergic conditions, working through different mechanisms than bronchodilators. *Terbutaline* - **Terbutaline** is a **short-acting beta-2 agonist (SABA)** used for bronchodilation in asthma and COPD [2]. - Available in **oral, inhaled, and injectable forms** for rapid relief of bronchospasm. *Salbutamol* - **Salbutamol** (also known as albuterol) is a **short-acting beta-2 agonist (SABA)** and the most widely used rescue inhaler for asthma [1], [2]. - Provides **rapid bronchodilation** by stimulating beta-2 receptors in airway smooth muscles [3]. *Bambuterol* - **Bambuterol** is a **long-acting beta-2 agonist (LABA)** that is a prodrug of **terbutaline**. - It is slowly converted to the active form in the body, providing **sustained bronchodilation** for maintenance therapy.
Question 4: All of the following drugs are used for the treatment of urinary incontinence except:
- A. Ipratropium (Correct Answer)
- B. Oxybutynin
- C. Tolterodine
- D. Darifenacin
Explanation: ***Ipratropium*** - **Ipratropium** is a short-acting muscarinic antagonist primarily used as a **bronchodilator** in obstructive lung diseases. - While it has anticholinergic properties, it is not typically used for **urinary incontinence** due to its limited systemic absorption and short duration of action, making it less effective for bladder control compared to other agents. *Oxybutynin* - **Oxybutynin** is a commonly prescribed **muscarinic antagonist** that acts by relaxing the bladder detrusor muscle, increasing bladder capacity and reducing involuntary contractions. - It is effective in treating **overactive bladder** and urge incontinence. *Tolterodine* - **Tolterodine** is a **muscarinic receptor antagonist** that specifically targets M2 and M3 receptors in the bladder, reducing bladder hyperreactivity. - It is used for the symptomatic treatment of **urge incontinence** and overactive bladder. *Darifenacin* - **Darifenacin** is a highly M3-selective muscarinic receptor antagonist, which means it primarily blocks the M3 receptors responsible for **detrusor muscle contraction**. - Its selectivity helps minimize side effects common to less selective anticholinergics and is used for the treatment of **overactive bladder** with symptoms of urgency, frequency, and urge incontinence.
Question 5: Which of the following antimicrobials should not be given to a chronic asthmatic patient managed on theophylline therapy?
- A. Amoxicillin
- B. Cefotaxime
- C. Erythromycin (Correct Answer)
- D. Cotrimoxazole
Explanation: ***Erythromycin*** - **Erythromycin**, a macrolide antibiotic, is a potent inhibitor of the **cytochrome P450 (CYP450) enzyme system**, specifically **CYP1A2**, which is the primary enzyme responsible for theophylline metabolism. - Co-administration of erythromycin can significantly **increase theophylline levels**, leading to toxicity such as **nausea, vomiting, seizures, or cardiac arrhythmias.** - This interaction is clinically significant and erythromycin should be avoided in patients on theophylline therapy. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic that has minimal interaction with theophylline metabolism. - It does not significantly inhibit the **CYP1A2 enzyme** and is generally considered safe to use with theophylline. *Cefotaxime* - **Cefotaxime**, a third-generation cephalosporin, does not significantly affect the metabolism of theophylline. - It does not inhibit **CYP1A2 enzymes** and is safe for use in patients on theophylline therapy. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) may slightly increase theophylline levels by inhibiting some CYP450 isoenzymes, but its effect is generally less pronounced than that of erythromycin. - While caution and monitoring are advised, it is not as strongly contraindicated as erythromycin due to a lower risk of significant toxicity in most cases.
Question 6: What is a contraindication of antimuscarinic drugs?
- A. Peptic ulcer
- B. Glaucoma (Correct Answer)
- C. Asthma
- D. Urinary incontinence
Explanation: ***Correct: Glaucoma*** - Antimuscarinic drugs cause **mydriasis (pupil dilation)** and **cycloplegia**, which increases intraocular pressure, especially in individuals with **narrow-angle glaucoma**. - In narrow-angle glaucoma, pupil dilation causes the peripheral iris to bunch up and block the trabecular meshwork, obstructing aqueous humor outflow. - This can precipitate an **acute angle-closure glaucoma attack**, a medical emergency, making glaucoma an **absolute contraindication** to antimuscarinic drugs. - This is one of the most important contraindications to remember for all anticholinergic medications. *Incorrect: Peptic ulcer* - Antimuscarinic drugs were **historically used to treat** peptic ulcer disease by reducing gastric acid secretion and gastrointestinal motility. - While they are no longer first-line therapy (replaced by proton pump inhibitors and H2 blockers), peptic ulcer is **not a contraindication**. - The main reason they fell out of favor was due to side effects and less efficacy compared to modern alternatives, not because they worsen the condition. *Incorrect: Asthma* - Some antimuscarinics (e.g., **ipratropium, tiotropium**) are actually used as **bronchodilators** in asthma and COPD management. - They work by blocking muscarinic receptors in airway smooth muscle, causing bronchodilation. - Therefore, asthma is a **treatment indication**, not a contraindication. *Incorrect: Urinary incontinence* - Antimuscarinic drugs are the **primary pharmacological treatment** for overactive bladder and urge incontinence. - They work by blocking M3 muscarinic receptors in the detrusor muscle, reducing bladder contractions. - Common drugs include oxybutynin, tolterodine, and solifenacin. - Urinary incontinence is a **treatment indication**, not a contraindication.
Question 7: Maximum effect of bronchodilatation in asthma is caused by -
- A. Beta 2-Agonist (Correct Answer)
- B. Corticosteroids
- C. Theophylline
- D. Anticholinergic
Explanation: ***Beta 2-Agonist*** - **Beta-2 agonists** directly relax bronchial smooth muscle by stimulating beta-2 adrenergic receptors, leading to significant and rapid bronchodilation. - This direct action on airway muscle relaxation makes them the most potent and fastest-acting bronchodilators for acute asthma symptoms. *Corticosteroids* - **Corticosteroids** reduce airway inflammation and hypersensitivity over time but do not provide immediate or maximal bronchodilation. - Their primary role is in long-term control of asthma, preventing exacerbations rather than acutely reversing bronchospasm. *Theophylline* - **Theophylline** is a methylxanthine that causes modest bronchodilation by inhibiting phosphodiesterase and blocking adenosine receptors. - It has a narrow therapeutic index, numerous side effects, and is less effective than beta-2 agonists for bronchodilation. *Anticholinergic* - **Anticholinergics** (e.g., ipratropium) block muscarinic receptors, preventing acetylcholine-induced bronchoconstriction. - They provide bronchodilation but are generally less potent and have a slower onset of action compared to beta-2 agonists in asthma.
Question 8: Tamsulosin belongs to
- A. α1a receptor agonist
- B. β-blockers
- C. 5α-reductase inhibitors
- D. α1a receptor blockers (Correct Answer)
Explanation: ***α1a receptor blockers*** - Tamsulosin is a **selective alpha-1a adrenergic receptor blocker**, which is primarily found in the smooth muscle of the prostate, bladder neck, and urethra. - By blocking these receptors, it causes **relaxation of the smooth muscle**, leading to improved urine flow in conditions like benign prostatic hyperplasia (BPH). *α1a receptor agonist* - An **agonist** would activate the alpha-1a receptors, leading to **contraction of smooth muscle**, which would worsen urinary symptoms in BPH. - This action is contrary to the therapeutic effect of tamsulosin. *β-blockers* - **Beta-blockers** primarily affect the heart and blood vessels by blocking beta-adrenergic receptors and are used for conditions like hypertension or angina. - They do not directly target the alpha-1a receptors in the prostate and would not alleviate BPH symptoms. *5α-reductase inhibitors* - **5-alpha reductase inhibitors** (e.g., finasteride, dutasteride) reduce the size of the prostate by inhibiting the conversion of testosterone to dihydrotestosterone. - They have a different mechanism of action and are used for long-term management of BPH to reduce prostate volume, whereas tamsulosin provides symptomatic relief.
Question 9: Which of the following statement is correct regarding the graph shown? (AllMS Nov 2016)
- A. Drug in graph A is epinephrine
- B. Effect on heart in graph A can be overcome by antimuscarinic
- C. Drug acting on graph C is nor-epinephrine
- D. Drug acting on graph B is isoproterenol (Correct Answer)
Explanation: ***Drug acting on graph B is isoproterenol*** - Graph B shows a definite **increase in pulse rate** and a **decrease in peripheral resistance**, while blood pressure remains largely unchanged due to the combined effects. - **Isoproterenol** is a non-selective β-adrenergic agonist that causes increased heart rate (β1 effect) and vasodilation leading to decreased peripheral resistance (β2 effect). - This unique hemodynamic profile is characteristic of isoproterenol and distinguishes it from other catecholamines. *Drug in graph A is epinephrine* - Graph A shows a **decrease in pulse rate**, which is **not characteristic** of epinephrine at the dose shown (10 μg/min). - Epinephrine typically causes **tachycardia** due to β1-adrenergic stimulation, not bradycardia. - The cardiovascular profile in graph A does not match epinephrine's expected effects. *Effect on heart in graph A can be overcome by antimuscarinic* - The decreased pulse rate in graph A suggests **reflex bradycardia** or parasympathetic stimulation. - However, without knowing the actual drug, we cannot definitively state whether antimuscarinic agents would reverse this effect. - This option makes assumptions that cannot be verified from the graph alone. *Drug acting on graph C is nor-epinephrine* - Graph C shows **increased pulse rate** and **decreased peripheral resistance** with slight drop in blood pressure. - **Norepinephrine** primarily acts on α1-receptors, causing **vasoconstriction and increased peripheral resistance**, not decreased. - Norepinephrine would also increase blood pressure significantly, which contradicts the graph. - This cardiovascular profile does not match norepinephrine.
Question 10: What is an atypical side effect of montelukast?
- A. Goodpasture syndrome
- B. Membranous glomerulonephritis
- C. Bronchial asthma
- D. Churg-Strauss syndrome (Correct Answer)
Explanation: ***Churg-Strauss syndrome*** - The apparent development of **Churg-Strauss syndrome** (eosinophilic granulomatosis with polyangiitis) has been reported in patients treated with montelukast, although it is believed to be related more to the unmasking of the disease rather than a direct drug effect. - This typically occurs when **corticosteroids** are tapered or withdrawn as montelukast takes over, revealing the underlying vasculitis. *Goodpasture syndrome* - **Goodpasture syndrome** is an autoimmune disease causing rapidly progressive glomerulonephritis and pulmonary hemorrhage, characterized by anti-glomerular basement membrane (GBM) antibodies. - There is no established association between montelukast use and the development of Goodpasture syndrome. *Membranous glomerulonephritis* - **Membranous glomerulonephritis** is a common cause of nephrotic syndrome, characterized by immune complex deposition on the glomerular basement membrane. - This condition is not typically linked to the use of montelukast. *Bronchial asthma* - **Bronchial asthma** is the condition montelukast is used to treat, acting as a leukotriene receptor antagonist to reduce inflammation and bronchoconstriction. - It is a primary indication for the drug, not a side effect.
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