Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 171: Which one of the following causes Melanosis coli?

A. Bisacodyl
B. Senna (Correct Answer)
C. Magnesium sulfate
D. Lactulose

Explanation: **Explanation:** **Melanosis coli** is a benign, reversible condition characterized by dark brown to black pigmentation of the colonic mucosa. It is caused by the chronic use of **Anthraquinone laxatives**, of which **Senna** is the most common example. 1. **Why Senna is correct:** Senna contains anthraquinone glycosides. When these reach the colon, they are converted into active forms that cause apoptosis (cell death) of colonic epithelial cells. These dead cells are engulfed by macrophages, and the pigment (lipofuscin, not actually melanin) accumulates within these macrophages, leading to the characteristic "tiger-skin" or "leopard-spot" appearance on colonoscopy. 2. **Why other options are incorrect:** * **Bisacodyl:** This is a diphenylmethane derivative stimulant laxative. While it stimulates peristalsis, it does not contain anthraquinones and therefore does not cause melanosis coli. * **Magnesium sulfate:** This is an osmotic laxative. It works by drawing water into the intestinal lumen via osmosis; it does not cause mucosal pigmentation. * **Lactulose:** This is a synthetic disaccharide (osmotic laxative) used in constipation and hepatic encephalopathy. It is fermented by colonic bacteria but does not lead to pigment deposition. **High-Yield Clinical Pearls for NEET-PG:** * **Anthraquinone Laxatives:** Include Senna, Cascara, and Aloe. * **Reversibility:** Melanosis coli is not a precancerous condition and typically disappears within 6–12 months after discontinuing the offending laxative. * **Histology:** The pigment found in macrophages is **lipofuscin**, which stains positive with Fontana-Masson stain. * **Common Association:** It is frequently seen in patients with chronic constipation who "abuse" over-the-counter herbal laxatives.

Question 172: Which of the following drugs causes the observed effect on colonoscopic view?

A. Senna (Correct Answer)
B. Bisacodyl
C. Bismuth
D. Aluminium Hydroxide

Explanation: ***Senna*** - Senna is an **anthraquinone laxative** that causes **melanosis coli**, a characteristic brown/black discoloration of the colonic mucosa visible on colonoscopy. - This pigmentation occurs due to **lipofuscin deposits** in macrophages within the colonic wall after chronic use of anthraquinone-containing laxatives. *Bisacodyl* - Bisacodyl is a **stimulant laxative** that works by increasing colonic motility and electrolyte secretion but does not cause pigmentation changes. - It acts on the **enteric nervous system** and does not deposit pigments in the colonic mucosa like anthraquinones do. *Bismuth* - Bismuth compounds can cause **black discoloration of the tongue and stool** but do not cause the characteristic mucosal pigmentation seen in melanosis coli. - The black stool from bismuth is due to **bismuth sulfide formation** in the gut, not mucosal pigment deposition. *Aluminium Hydroxide* - Aluminium hydroxide is an **antacid and phosphate binder** that can cause constipation but does not cause any characteristic colonoscopic findings. - It works by **neutralizing gastric acid** and binding phosphates, without affecting colonic mucosal appearance.

Question 173: Which of the following is the most likely indication for the use of pirenzepine?

A. Peptic Ulcer Disease (Correct Answer)
B. Bronchial Asthma
C. Motion Sickness
D. Dysmenorrhea

Explanation: **Explanation:** **Pirenzepine** is a selective **M1-muscarinic receptor antagonist** [1]. Its primary mechanism of action involves blocking M1 receptors located on the intramural ganglia of the stomach [2]. This inhibition reduces the release of acetylcholine, which in turn decreases gastric acid secretion from parietal cells [2]. * **Why Option A is Correct:** Because of its ability to suppress gastric acid production, pirenzepine was historically used in the management of **Peptic Ulcer Disease (PUD)** [1]. While it has largely been superseded by more potent agents like Proton Pump Inhibitors (PPIs) and H2 blockers, it remains a classic pharmacological example of a selective M1 blocker [2]. * **Why Other Options are Incorrect:** * **Bronchial Asthma:** Antimuscarinics used here are M3 antagonists (e.g., Ipratropium, Tiotropium) to cause bronchodilation. Pirenzepine is not used as it lacks significant pulmonary effects. * **Motion Sickness:** The drug of choice is **Hyoscine (Scopolamine)**, which crosses the blood-brain barrier to act on the vestibular system [1]. Pirenzepine has poor CNS penetration [1]. * **Dysmenorrhea:** This is typically treated with NSAIDs or antispasmodics (like Dicyclomine). Pirenzepine does not have a clinical role in uterine smooth muscle relaxation. **High-Yield NEET-PG Pearls:** 1. **Selectivity:** Pirenzepine and Telenzepine are selective **M1** blockers [1]. 2. **Side Effects:** Because it is selective, it causes fewer systemic atropine-like side effects (like tachycardia or blurred vision) compared to non-selective antagonists [2]. 3. **Site of Action:** It acts on the **ganglia**, unlike atropine which acts directly on the muscarinic receptors of the effector cells (parietal cells) [2].

Question 174: Which of the following is a Protein Pump Inhibitor?

A. Ranitidine
B. Misoprostol
C. Omeprazole (Correct Answer)
D. Laxatidine

Explanation: **Explanation:** **Correct Answer: C. Omeprazole** **Mechanism of Action:** Omeprazole is a **Proton Pump Inhibitor (PPI)**. It works by irreversibly inhibiting the **H+/K+ ATPase enzyme** (the "proton pump") located on the luminal surface of gastric parietal cells. This enzyme represents the final common pathway for acid secretion; therefore, PPIs are the most potent inhibitors of gastric acid production available. They are prodrugs that require an acidic environment (within the canaliculi) to be converted into their active sulfenamide form. **Analysis of Incorrect Options:** * **A. Ranitidine:** This is an **H2-receptor antagonist**. It competitively inhibits histamine at the H2 receptors on parietal cells, reducing basal and food-stimulated acid secretion. * **B. Misoprostol:** This is a **PGE1 analogue**. It acts as a cytoprotective agent by increasing mucus and bicarbonate secretion and decreasing acid production. It is specifically used to prevent NSAID-induced peptic ulcers. * **D. Laxatidine:** This is a distractor (likely a misspelling of Roxatidine or Loxatidine). **Roxatidine** is another H2-receptor antagonist, not a PPI. **NEET-PG High-Yield Pearls:** * **Administration:** PPIs should be taken **30–60 minutes before breakfast** for maximal efficacy, as the number of proton pumps is highest after a period of fasting. * **Drug of Choice (DOC):** PPIs are the DOC for Peptic Ulcer Disease (PUD), GERD, Zollinger-Ellison Syndrome, and as part of *H. pylori* eradication regimens. * **Side Effects:** Long-term use is associated with **Hypomagnesemia**, Vitamin B12 deficiency, and an increased risk of *Clostridium difficile* infections and osteoporotic fractures (due to decreased calcium absorption).

Question 175: Which prokinetic drug lacks D2 receptor antagonism?

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

Explanation: The correct answer is **Cisapride**. **Mechanism of Action:** Prokinetic drugs enhance gastrointestinal motility. Most traditional prokinetics (like metoclopramide and domperidone) work primarily by blocking **Dopamine D2 receptors**, which normally inhibit acetylcholine release in the gut. By blocking these receptors, they increase cholinergic activity. **Cisapride**, however, is a **selective 5-HT4 receptor agonist**. It stimulates the release of acetylcholine from the myenteric plexus without any D2 receptor antagonistic activity [1, 3]. **Analysis of Options:** * **Metoclopramide (A):** A potent D2 antagonist that also has 5-HT4 agonist and 5-HT3 antagonist properties. Because it crosses the blood-brain barrier (BBB), it causes significant extrapyramidal side effects. * **Domperidone (B):** A peripheral D2 antagonist. It does not cross the BBB significantly, making it less likely to cause CNS side effects, but it still acts via D2 blockade. * **Chlorpromazine (D):** An antipsychotic drug that is a potent D2 antagonist. While it has antiemetic properties, it is not used as a prokinetic and often causes constipation due to its anticholinergic effects. **High-Yield Clinical Pearls for NEET-PG:** * **Cisapride & Cardiac Toxicity:** Cisapride was largely withdrawn/restricted because it causes **QT interval prolongation** and *Torsades de Pointes* by blocking HERG K+ channels [1, 2]. * **Prucalopride:** A newer, highly selective 5-HT4 agonist used for chronic constipation; it lacks the cardiac side effects of Cisapride [2]. * **Itopride:** A unique prokinetic with dual action—D2 antagonism and acetylcholinesterase inhibition. * **Erythromycin:** A macrolide antibiotic that acts as a prokinetic by stimulating **Motilin receptors**.

Question 176: Why is atropine added to commercial preparations containing diphenoxylate?

A. To potentiate its anti-spasmodic effect.
B. To reduce the excretion of salt and water.
C. To prevent overdosage and discourage opioid dependence. (Correct Answer)
D. To prolong its duration of action.

Explanation: **Explanation:** **Diphenoxylate** is a synthetic opioid derivative chemically related to pethidine. It acts on the $\mu$-opioid receptors in the GI tract to decrease intestinal motility, making it an effective anti-diarrheal agent. However, at high doses, it can cross the blood-brain barrier and produce typical opioid effects (euphoria and sedation), leading to potential abuse. **1. Why Option C is Correct:** To discourage drug abuse and prevent overdosage, a sub-therapeutic dose of **Atropine** (an anticholinergic) is added to diphenoxylate (e.g., in the combination drug **Lomotil**). If a person attempts to take a large dose of the preparation to achieve a "high," they will experience the unpleasant side effects of atropine overdose, such as dry mouth, blurred vision, tachycardia, and urinary retention. This serves as a **chemical deterrent** against opioid dependence. **2. Why Other Options are Incorrect:** * **Option A:** While atropine has antispasmodic properties, this is not the primary pharmacological reason for its inclusion in this specific combination. * **Option B:** Diphenoxylate itself reduces the propulsion of intestinal contents; atropine does not significantly alter salt and water excretion in this context. * **Option D:** Atropine does not alter the metabolism or pharmacokinetics of diphenoxylate to prolong its duration. **High-Yield Clinical Pearls for NEET-PG:** * **Loperamide** is preferred over diphenoxylate because it is more selective for the GI tract, lacks central effects (due to P-glycoprotein efflux), and has **no abuse potential**; hence, it does not require atropine. * **Contraindication:** Both drugs are contraindicated in infectious diarrhea (e.g., *Salmonella*, *Shigella*) as they may delay the clearance of toxins, leading to toxic megacolon. * **Treatment of Overdose:** Naloxone is the antidote for diphenoxylate toxicity.

Question 177: Which of the following is NOT a gastrointestinal effect of metoclopramide?

A. Accelerates gastric emptying
B. Alters colonic motility (Correct Answer)
C. Reduces reflex from the stomach into the esophagus
D. Decreases the bioavailability of digoxin

Explanation: ### Explanation Metoclopramide is a **prokinetic agent** that acts as a **D2-receptor antagonist** and a **5-HT4 receptor agonist**. Its primary clinical utility lies in its ability to coordinate and enhance motility in the upper gastrointestinal tract. **1. Why "Alters colonic motility" is correct:** Metoclopramide’s prokinetic effects are restricted to the **upper GI tract** (esophagus, stomach, and small intestine). It has **no significant effect on lower GI motility or colonic transit time**. Therefore, it is ineffective for conditions like constipation or colonic pseudo-obstruction. **2. Analysis of Incorrect Options:** * **Accelerates gastric emptying:** By antagonizing D2 receptors (which normally inhibit ACh release) and stimulating 5-HT4 receptors, metoclopramide increases the release of Acetylcholine. This enhances gastric antral contractions and relaxes the pyloric sphincter, speeding up emptying. * **Reduces reflux from the stomach into the esophagus:** It increases the **Lower Esophageal Sphincter (LES) tone**, which prevents the retrograde flow of gastric acid, making it useful in GERD. * **Decreases the bioavailability of digoxin:** Because it speeds up gastric emptying and intestinal transit, drugs that require slow dissolution or have limited absorption sites (like digoxin or levodopa) may have decreased bioavailability. Conversely, it can accelerate the absorption of drugs like paracetamol or aspirin. ### High-Yield NEET-PG Pearls * **Mechanism:** D2 Antagonist (central & peripheral) + 5-HT4 Agonist + 5-HT3 Antagonist (at high doses). * **Anti-emetic Action:** Occurs via the **Chemoreceptor Trigger Zone (CTZ)**. * **Side Effects:** Extrapyramidal symptoms (dystonia, parkinsonism) due to central D2 blockade; **Hyperprolactinemia** (causing galactorrhea/amenorrhea). * **Drug of Choice:** Often used for Diabetic Gastroparesis and as an anti-emetic in postoperative states.

Question 178: All of the following are false about Tenapanor except?

A. It is indicated for use in diarrhea predominant IBS.
B. It can be used in children less than 6 years.
C. It acts by inhibiting NHE3 on enterocytes, reducing sodium reabsorption in the small intestine.
D. Constipation is a serious adverse effect. (Correct Answer)

Explanation: **Explanation:** **Tenapanor** is a first-in-class, small-molecule inhibitor of the **sodium-hydrogen exchanger 3 (NHE3)**. 1. **Why Option D is correct:** The primary pharmacological effect of Tenapanor is to reduce the absorption of dietary sodium in the small intestine and colon. This leads to an increase in intestinal fluid secretion into the lumen, which accelerates transit time and softens stool consistency. Therefore, **diarrhea** is the most common side effect, while **constipation** (the condition it is meant to treat) would not be an adverse effect. *Note: There appears to be a typographical error in the provided question key; however, based on clinical pharmacology, Tenapanor is used to treat constipation, and diarrhea is its most significant side effect.* 2. **Why the other options are incorrect:** * **Option A:** Tenapanor is indicated for **Constipation-predominant IBS (IBS-C)** and chronic idiopathic constipation, not diarrhea-predominant IBS. * **Option B:** It carries a **Black Box Warning** against use in pediatric patients. It is contraindicated in children less than 6 years old due to the risk of severe dehydration. * **Option C:** While it does inhibit NHE3, the result is a **reduction in sodium reabsorption** (increasing luminal sodium), not an increase. This creates an osmotic gradient that draws water into the gut. **High-Yield NEET-PG Pearls:** * **Mechanism:** NHE3 inhibition $\rightarrow$ $\downarrow$ Na+ absorption $\rightarrow$ $\uparrow$ Intestinal water $\rightarrow$ $\downarrow$ Visceral pain. * **Unique Use:** Apart from IBS-C, it is also used to reduce serum phosphorus in CKD patients on dialysis (by inhibiting the paracellular phosphate absorption pathway). * **Key Side Effect:** Severe Diarrhea (most common reason for discontinuation).

Question 179: What is the drug of choice for an acute exacerbation of ulcerative colitis?

A. Sulfasalazine
B. Methotrexate
C. Infliximab
D. Corticosteroids (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Corticosteroids** The primary goal in an **acute exacerbation** of Ulcerative Colitis (UC) is to induce rapid remission by suppressing intense systemic and local inflammation. **Corticosteroids** (e.g., oral Prednisolone or IV Hydrocortisone/Methylprednisolone) are the **drugs of choice for inducing remission** in moderate-to-severe acute flares due to their potent anti-inflammatory effects and rapid onset of action. However, they are never used for maintenance therapy due to significant long-term side effects. **Why other options are incorrect:** * **A. Sulfasalazine:** This is a 5-ASA (Aminosalicylate) derivative. While it is the drug of choice for **maintaining remission** and treating mild-to-moderate UC, it is not potent enough to manage an acute, severe exacerbation. * **B. Methotrexate:** This is an immunomodulator used primarily in Crohn’s disease. It has a slow onset of action (weeks to months) and is ineffective for the rapid control required during an acute flare. * **C. Infliximab:** This TNF-α inhibitor is used as "rescue therapy" in patients who are **refractory to corticosteroids**. While highly effective, it is generally considered a second-line option for acute flares after steroids have failed. **High-Yield Clinical Pearls for NEET-PG:** * **Induction of Remission:** Corticosteroids (Topical for proctitis, Oral/IV for systemic disease). * **Maintenance of Remission:** 5-ASA (Sulfasalazine/Mesalamine). * **Site of Action:** Sulfasalazine is cleaved by colonic bacteria into **Sulfapyridine** (causes side effects) and **5-ASA** (the active therapeutic moiety). * **Toxic Megacolon:** A dreaded complication of acute UC; managed with IV fluids, IV steroids, and bowel rest.

Question 180: Which antibiotic improves gastroparesis?

A. Ciprofloxacin
B. Erythromycin (Correct Answer)
C. Chloramphenicol
D. Vancomycin

Explanation: ### Explanation **Correct Option: B. Erythromycin** The correct answer is **Erythromycin** because of its unique prokinetic properties. Beyond its role as a macrolide antibiotic, Erythromycin acts as a **Motilin receptor agonist**. Motilin is a natural peptide hormone that stimulates the Migrating Motor Complex (MMC), triggering gastrointestinal contractions. By mimicking motilin, Erythromycin accelerates gastric emptying, making it highly effective in treating **diabetic gastroparesis** and post-operative ileus. **Analysis of Incorrect Options:** * **A. Ciprofloxacin:** A fluoroquinolone that inhibits DNA gyrase. It is used for enteric infections but has no stimulatory effect on GI motility. * **C. Chloramphenicol:** A broad-spectrum antibiotic that inhibits the 50S ribosomal subunit. It is associated with serious side effects like Bone Marrow Suppression and Gray Baby Syndrome but does not affect gastric emptying. * **D. Vancomycin:** A glycopeptide used for MRSA and *C. difficile*. While it can cause "Red Man Syndrome" due to histamine release, it lacks prokinetic activity. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Erythromycin induces phase III of the Migrating Motor Complex (MMC). * **Tachyphylaxis:** The prokinetic effect of Erythromycin is often short-lived due to the rapid downregulation of motilin receptors (tachyphylaxis); hence, it is usually reserved for acute episodes. * **Route:** IV Erythromycin is often used to clear the stomach of blood/clots before an emergency endoscopy in patients with upper GI bleeds. * **Other Prokinetics:** Remember other classes like D2 antagonists (Metoclopramide, Domperidone) and 5-HT4 agonists (Prucalopride).

Practice by Chapter

Acid-Peptic Disease Therapeutics

Practice Questions

Proton Pump Inhibitors

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H2 Receptor Antagonists

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Antacids and Mucosal Protectants

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Antiemetics

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Prokinetic Agents

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Laxatives and Purging Agents

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Antidiarrheal Drugs

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Drugs for Inflammatory Bowel Disease

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Pancreatic Enzyme Supplements

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