Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 341: Which of the following best describes the mechanism of action of Lubiprostone?

A. Chloride channel activator (Correct Answer)
B. Chloride channel inhibitor
C. Sodium channel activator
D. Sodium channel inhibitor

Explanation: ***Chloride channel activator*** - Lubiprostone is a **prostaglandin E1 derivative** that specifically activates **chloride channels (ClC-2)** on the apical membrane of intestinal epithelial cells. - This activation leads to an increase in **fluid secretion into the intestinal lumen**, softening stool and promoting bowel movements. *Chloride channel inhibitor* - Medications that inhibit chloride channels would likely **reduce fluid secretion** in the intestines, potentially worsening constipation. - This mechanism is **opposite** to the therapeutic effect of lubiprostone, which aims to increase fluid content in the stool. *Sodium channel activator* - Activating sodium channels in the intestine could lead to increased fluid absorption or altered electrolyte balance, but this is **not the primary mechanism** of action for lubiprostone. - Lubiprostone's effect is centered around **anion (chloride) secretion**, not direct sodium channel activation. *Sodium channel inhibitor* - Inhibiting sodium channels might reduce sodium absorption, potentially increasing luminal water, but this is **not how lubiprostone works**. - Lubiprostone specifically targets **chloride channels** to achieve its cathartic effect.

Question 342: A patient with diabetic gastroparesis is treated with erythromycin primarily due to its ability to:

A. Increase gastric motility
B. Decrease gastric motility
C. Bind to motilin receptors (Correct Answer)
D. Act as a motilin analogue

Explanation: ***Bind to motilin receptors*** - Erythromycin acts as a **motilin receptor agonist**, mimicking the action of the endogenous hormone motilin, which stimulates gastrointestinal motility. - This binding leads to increased **gastric contractions** and improved gastric emptying, addressing the primary problem in gastroparesis. *Increase gastric motility* - While erythromycin *does* increase gastric motility, this option describes the **effect** rather than the primary mechanism of action (binding to motilin receptors). - Understanding the receptor binding is crucial for grasping why erythromycin is effective in this context. *Decrease gastric motility* - Decreasing gastric motility would **worsen** diabetic gastroparesis, a condition already characterized by delayed gastric emptying. - Erythromycin's therapeutic effect is the exact opposite of decreasing motility. *Act as a motilin analogue* - Erythromycin is not a direct motilin analogue in terms of its chemical structure, but it **mimics motilin's effects** by binding to its receptors. - The precise mechanism is its binding to the receptors, rather than being classified as a structural analogue.

Question 343: Which of the following is an H2 receptor antagonist used as an anti-ulcer drug?

A. Pirenzepine
B. Famotidine (Correct Answer)
C. Rabeprazole
D. Sucralfate

Explanation: ***Famotidine*** - **Famotidine** is a potent and selective **H2 receptor antagonist** that works by blocking histamine H2 receptors on parietal cells, thereby reducing gastric acid secretion. - It is widely used for the treatment of **peptic ulcers**, gastroesophageal reflux disease (**GERD**), and other acid-related disorders. *Pirenzepine* - **Pirenzepine** is a **selective M1 muscarinic antagonist**, which inhibits gastric acid secretion by blocking cholinergic pathways. - While it was previously used as an anti-ulcer drug, its mechanism of action is distinct from H2 receptor antagonism. *Rabeprazole* - **Rabeprazole** is a **proton pump inhibitor (PPI)** that irreversibly blocks the H+/K+-ATPase pump in gastric parietal cells, leading to a profound and prolonged reduction in gastric acid production. - Its mechanism is different from H2 receptor antagonists. *Sucralfate* - **Sucralfate** is a **cytoprotective agent** that forms a viscous, protective gel that adheres to ulcerated areas, shielding them from acid, pepsin, and bile. - It does not directly inhibit acid secretion but rather provides a physical barrier and promotes healing.

Question 344: Antacid drug that typically causes diarrhea.

A. Sodium bicarbonate
B. Magnesium hydroxide (Correct Answer)
C. Calcium carbonate
D. Aluminium hydroxide

Explanation: ***Magnesium hydroxide*** - **Magnesium-containing antacids** commonly cause **diarrhea** due to their osmotic laxative effect, drawing water into the intestines. - The magnesium ions are poorly absorbed and act as an **osmotic agent** in the gut lumen. *Sodium bicarbonate* - **Sodium bicarbonate** can cause **systemic alkalosis** due to absorption of bicarbonate ions, especially with high doses or impaired renal function. - It does not typically cause diarrhea; instead, the CO2 produced from its reaction with stomach acid can cause **belching** and gastric distension. *Calcium carbonate* - **Calcium carbonate** is more frequently associated with **constipation** due to calcium's ability to slow intestinal motility. - Excessive use can lead to **hypercalcemia** and milk-alkali syndrome. *Aluminium hydroxide* - **Aluminium-containing antacids** are notorious for causing **constipation** by slowing gut motility. - Long-term use can also lead to **hypophosphatemia** as aluminum binds to phosphate in the GI tract.

Question 345: Proton pump inhibitors for peptic ulcer disease should be taken:

A. Before Breakfast (Correct Answer)
B. After Breakfast
C. Before Dinner
D. After Dinner

Explanation: ***Before Breakfast*** - Proton pump inhibitors (PPIs) are most effective when taken **30-60 minutes before the first meal of the day**. - This timing allows the drug to reach peak plasma concentration when the greatest number of **proton pumps** are activated by food intake, maximizing their inhibitory effect on acid secretion. *After Breakfast* - Taking PPIs after breakfast significantly reduces their effectiveness because many **proton pumps** would have already been active and subsequently inactivated before the drug can exert its full effect. - This timing leads to suboptimal acid suppression, potentially hindering the healing of **peptic ulcers**. *Before Dinner* - While taking a second daily dose before dinner can be beneficial for some patients with persistent symptoms, it is not the primary or most effective administration time for a **once-daily dose**. - The main goal is to suppress the **meal-stimulated acid secretion** throughout the day, which is best achieved by the morning dose. *After Dinner* - Administering PPIs after dinner is generally ineffective for the same reasons as taking them after breakfast; the **proton pumps** have already been activated and then inactivated, diminishing the drug's impact. - This timing would lead to inadequate acid control, especially during the day when most acid secretion occurs.

Question 346: Proton pump inhibitors are most effective when they are given:

A. After meals
B. Shortly before meals (Correct Answer)
C. Along with H2 blockers
D. During prolonged fasting periods

Explanation: ***Shortly before meals*** - **Proton pump inhibitors (PPIs)** are most effective when administered 30-60 minutes before a meal because they need to be present when **parietal cells are actively secreting acid**. - PPIs are **prodrugs** that become activated in the acidic environment of the parietal cell secretory canaliculus and then irreversibly bind to the **H+/K+ ATPase pump**. - Taking them before a meal ensures that the drug is absorbed and reaches the parietal cells just as they are being stimulated to secrete acid in response to food, maximizing the number of pumps that can be inhibited. *After meals* - Taking PPIs after meals is less effective because a significant portion of the drug may have already been absorbed during a period of lower parietal cell activity. - This timing misses the optimal window when the maximum number of **proton pumps** are being inserted into the canalicular membrane in response to the meal stimulus. - Additionally, food can interfere with the absorption of some PPIs, further reducing effectiveness. *Along with H2 blockers* - While both PPIs and **H2 blockers** reduce gastric acid through different mechanisms, combining them does not provide significant additional benefit for most conditions. - H2 blockers reduce the basal stimulation of parietal cells, which means fewer pumps are actively secreting when the PPI is present, potentially reducing the number of pumps available for PPI binding. - Routine combination therapy is generally not recommended except in specific refractory cases. *During prolonged fasting periods* - During **fasting**, parietal cells are relatively inactive with minimal pump activity in the secretory canaliculus. - PPIs are most effective when they can bind to actively functioning **H+/K+ ATPase pumps**, which are minimal during fasting states. - This results in fewer pumps being irreversibly inhibited, leading to suboptimal acid suppression.

Question 347: Which of the following drugs does not stimulate 5-HT4 receptors?

A. Cisapride
B. Renzapride
C. Metoclopramide
D. Domperidone (Correct Answer)

Explanation: ***Domperidone*** - Domperidone is a **dopamine D2 receptor antagonist** that acts as an antiemetic and prokinetic agent. - Unlike the other options, it primarily works by blocking D2 receptors in the **chemoreceptor trigger zone** and gastrointestinal tract, and does **not directly stimulate 5-HT4 receptors**. - Its prokinetic effects are achieved through **D2 receptor antagonism**, which increases gastrointestinal motility by removing dopaminergic inhibition of acetylcholine release. *Renzapride* - Renzapride is a **5-HT4 receptor agonist** and a 5-HT3 receptor antagonist, making it a powerful prokinetic agent. - Its prokinetic effects are directly mediated through the **stimulation of 5-HT4 receptors**, increasing gastrointestinal motility [1]. *Metoclopramide* - Metoclopramide is a **dopamine D2 receptor antagonist** with some **5-HT4 receptor agonist** activity [2]. - The 5-HT4 receptor agonism contributes to its prokinetic effects by enhancing acetylcholine release in the enteric nervous system [1]. *Cisapride* - Cisapride is a **selective 5-HT4 receptor agonist** that significantly increases gastrointestinal motility. - Its prokinetic action is almost entirely dependent on the **stimulation of 5-HT4 receptors**, leading to enhanced release of acetylcholine [1].

Practice by Chapter

Acid-Peptic Disease Therapeutics

Practice Questions

Proton Pump Inhibitors

Practice Questions

H2 Receptor Antagonists

Practice Questions

Antacids and Mucosal Protectants

Practice Questions

Antiemetics

Practice Questions

Prokinetic Agents

Practice Questions

Laxatives and Purging Agents

Practice Questions

Antidiarrheal Drugs

Practice Questions

Drugs for Inflammatory Bowel Disease

Practice Questions

Pancreatic Enzyme Supplements

Practice Questions

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