Drugs for Gastrointestinal Diseases — MCQs

A patient presented with abdominal pain and frequent unsatisfactory bowel movements. For the last year, he has been using a purgative twice weekly to open his bowel. On colonoscopy, the colon was found to be atonic with bluish pigmentation of the mucosa. Which is the most likely purgative that the patient has been using?

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 141: Which of the following statements about household emetics is incorrect?

A. Ipecac syrup is potent and safe.
B. A solution of sodium chloride in warm water is the safest emetic.
C. Apomorphine is effective when administered orally. (Correct Answer)
D. Tickling the fauces with a tongue depressor is the best method to induce emesis.

Explanation: ### Explanation **1. Why Option C is the Correct Answer (Incorrect Statement):** Apomorphine is a potent dopaminergic agonist that acts directly on the **Chemoreceptor Trigger Zone (CTZ)** in the medulla to induce vomiting. However, it undergoes extensive **first-pass metabolism** in the liver, making it virtually ineffective when administered orally. To induce emesis, it must be administered via **subcutaneous injection**, where it typically acts within 5–10 minutes. **2. Analysis of Other Options:** * **Option A (Ipecac Syrup):** Derived from *Cephaelis ipecacuanha*, it contains alkaloids (emetine and cephaeline) that irritate the gastric mucosa and stimulate the CTZ. It is considered relatively safe and potent but has largely fallen out of clinical favor due to the risk of aspiration and delayed gastric decontamination. * **Option B (Sodium Chloride):** While a common "household" recommendation, salt water is generally considered the **safest** in terms of pharmacological toxicity compared to drugs; however, it is often unreliable and carries a risk of fatal hypernatremia if emesis fails. * **Option D (Tickling the Fauces):** Mechanical stimulation of the pharynx (gag reflex) is the **best/first-line** recommended method for immediate induction of emesis in a household setting because it is non-toxic, instantaneous, and does not involve chemical ingestion. **Clinical Pearls for NEET-PG:** * **Contraindications to Emetics:** Never induce vomiting in cases of **corrosive poisoning** (acid/alkali), **hydrocarbon/petroleum** ingestion (risk of aspiration pneumonia), or in **unconscious/convulsing** patients. * **Drug of Choice for Emesis:** In a clinical setting, **Apomorphine (SC)** is the most reliable, while **Syrup Ipecac** is the traditional oral agent. * **Gastric Lavage:** Most effective if performed within **1 hour** of poison ingestion.

Question 142: Lubiprostone is:

A. A new anticholinergic antidiarrhoeal drug.
B. A serotonin agonist.
C. A new drug to treat peptic ulcers.
D. A drug used to treat irritable bowel syndrome. (Correct Answer)

Explanation: **Explanation:** **Lubiprostone** is a bicyclic fatty acid derivative that acts as a **selective chloride channel activator (Type-2 ClC-2)**. By activating these channels in the apical membrane of the intestinal epithelium, it increases the secretion of chloride-rich intestinal fluid. This fluid enhances intestinal motility and softens the stool, facilitating easier passage without significantly affecting serum electrolyte levels. **Why Option D is correct:** Lubiprostone is FDA-approved for the treatment of **Irritable Bowel Syndrome with Constipation (IBS-C)** in adult women, as well as Chronic Idiopathic Constipation (CIC) and Opioid-Induced Constipation (OIC). **Analysis of Incorrect Options:** * **Option A:** It is not an anticholinergic; in fact, it is used to treat constipation, whereas anticholinergics typically cause constipation as a side effect. * **Option B:** It is not a serotonin (5-HT) agonist. While drugs like Tegaserod (5-HT4 agonist) are used for IBS-C, Lubiprostone’s mechanism is strictly via chloride channels. * **Option C:** It has no role in the management of peptic ulcer disease, which is treated with PPIs, H2 blockers, or mucosal protectants. **NEET-PG High-Yield Pearls:** * **Mechanism of Action:** Selective ClC-2 chloride channel activator. * **Primary Indication:** IBS-C (specifically in women >18 years) and Opioid-Induced Constipation. * **Common Side Effect:** Nausea (due to delayed gastric emptying) is the most frequently reported adverse effect. * **Pregnancy Category:** It is generally avoided in pregnancy (Category C) due to potential fetal loss risks observed in animal studies. * **Comparison:** Unlike **Linaclotide** (which acts via Guanylate Cyclase-C), Lubiprostone acts directly on chloride channels.

Question 143: Linaclotide is a:

A. Chloride channel activator
B. CFTR blocker
C. Somatostatin antagonist
D. Guanylate cyclase agonist (Correct Answer)

Explanation: **Explanation:** **Linaclotide** is a minimally absorbed synthetic peptide used primarily in the management of **Irritable Bowel Syndrome with Constipation (IBS-C)** and **Chronic Idiopathic Constipation (CIC)**. **1. Why Option D is Correct:** Linaclotide acts as a **Guanylate Cyclase-C (GC-C) agonist** on the luminal surface of the intestinal epithelium. Activation of GC-C leads to an increase in intracellular and extracellular **cyclic guanosine monophosphate (cGMP)**. * **Intracellular cGMP** activates the CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) ion channel, leading to the secretion of chloride and bicarbonate into the intestinal lumen. This results in increased intestinal fluid and accelerated transit. * **Extracellular cGMP** is believed to decrease the activity of pain-sensing nerves, thereby reducing visceral abdominal pain. **2. Why Other Options are Incorrect:** * **Option A:** **Lubiprostone** is the prototypical **Chloride channel activator** (specifically ClC-2). While it has a similar clinical effect to Linaclotide, its molecular target is different. * **Option B:** CFTR blockers (like Crofelemer) are used to treat diarrhea, not constipation. Linaclotide actually *activates* the CFTR pathway indirectly. * **Option C:** Somatostatin *analogs* (like Octreotide) are used to treat secretory diarrhea and variceal bleeding; they are not related to Linaclotide’s mechanism. **3. NEET-PG High-Yield Pearls:** * **Plecanatide** is another GC-C agonist similar to Linaclotide. * **Main Side Effect:** Diarrhea is the most common adverse effect. * **Contraindication:** It is contraindicated in pediatric patients under 6 years of age due to the risk of serious dehydration. * **Comparison:** Remember **L**inaclotide = **L**uminal Guanylate Cyclase; **L**ubiprostone = **L**ocal Chloride Channel.

Question 144: All of the following drugs may be used for motion sickness except?

A. Hyoscine
B. Dicyclomine
C. Domperidone (Correct Answer)
D. Scopolamine

Explanation: **Explanation:** The primary mechanism of motion sickness involves the stimulation of the vestibular system, which sends signals to the vomiting center via **muscarinic (M1)** and **histaminergic (H1)** receptors. **Why Domperidone is the correct answer:** Domperidone is a peripheral **Dopamine (D2) receptor antagonist**. While D2 antagonists (like Metoclopramide or Domperidone) are effective for drug-induced vomiting or gastroparesis by acting on the Chemoreceptor Trigger Zone (CTZ), they are **ineffective for motion sickness**. This is because the vestibular pathway does not rely on dopaminergic signaling. Furthermore, Domperidone does not cross the blood-brain barrier significantly. **Analysis of incorrect options:** * **Hyoscine (Scopolamine):** Options A and D are synonymous. Hyoscine is an anticholinergic drug and is considered the **drug of choice** for the prophylaxis of motion sickness. It works by blocking M1 receptors in the vestibular apparatus and the vomiting center. It is most effective when administered as a transdermal patch behind the ear (pinna). * **Dicyclomine:** This is also an anticholinergic (antimuscarinic) drug. While more commonly used as a GI antispasmodic, its antimuscarinic properties allow it to be used in the management of motion sickness, although it is less preferred than Hyoscine. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (Prophylaxis):** Hyoscine (Scopolamine). Must be given *before* the journey starts. * **Antihistaminics used:** Cyclizine, Meclizine, and Promethazine (useful for longer journeys due to longer duration of action). * **Site of action:** Motion sickness originates in the **labyrinth (vestibular system)**, not the CTZ. * **Key Receptors:** M1 and H1 are the targets for motion sickness; D2 and 5-HT3 are the targets for chemotherapy-induced nausea and vomiting (CINV).

Question 145: Which sulphonamide is used for the treatment of ulcerative colitis?

A. Sulphamethiazole
B. Sulphathalazole
C. Sulphaguanidine
D. Salazopyrin (Correct Answer)

Explanation: **Explanation:** **Salazopyrin** (also known as **Sulfasalazine**) is the correct answer. It is a prodrug composed of two moieties: **5-Aminosalicylic acid (5-ASA)** and **Sulfapyridine**, linked by a covalent azo bond. * **Mechanism of Action:** When taken orally, the drug reaches the colon unchanged. Colonic bacteria possess the enzyme **azoreductase**, which cleaves the bond, releasing 5-ASA and sulfapyridine. * **Therapeutic Effect:** 5-ASA (Mesalamine) is the active anti-inflammatory component that acts locally on the colonic mucosa by inhibiting prostaglandin and leukotriene synthesis. Sulfapyridine acts merely as a carrier to prevent premature absorption in the small intestine, though it is responsible for most of the drug's side effects (e.g., rashes, agranulocytosis). **Analysis of Incorrect Options:** * **Sulphamethiazole:** A rapidly absorbed and excreted sulfonamide primarily used for urinary tract infections (UTIs). * **Sulphathalazole & Sulphaguanidine:** These are "gut-acting" sulfonamides that are poorly absorbed from the GIT. While they were historically used for bacterial gastroenteritis or to "sterilize" the bowel before surgery, they lack the specific anti-inflammatory properties of 5-ASA required to treat ulcerative colitis. **NEET-PG High-Yield Pearls:** * **Drug of Choice:** While Sulfasalazine is classic, **Mesalamine (5-ASA)** formulations (like pH-dependent granules) are now preferred to avoid the systemic toxicity of the sulfa moiety. * **Side Effects:** Sulfasalazine can cause **reversible oligospermia** and requires **folic acid supplementation** as it inhibits folate absorption. * **Other Uses:** Sulfasalazine is also used as a Disease-Modifying Antirheumatic Drug (**DMARD**) in Rheumatoid Arthritis.

Question 146: Which of the following drugs is not used for motion sickness?

A. Metoclopramide (Correct Answer)
B. Cyclizine
C. Cinnarizine
D. Scopolamine

Explanation: Motion sickness is primarily mediated by the **vestibular system**, where sensory input is processed via **H1 (Histamine)** and **M1 (Muscarinic)** receptors. To be effective, a drug must act on these specific receptors within the vestibular apparatus or the vomiting center [1]. **Why Metoclopramide is the correct answer:** Metoclopramide is a **D2-receptor antagonist** and a prokinetic agent. It acts primarily on the **Chemoreceptor Trigger Zone (CTZ)** and the gastrointestinal tract. Since the CTZ is not the primary pathway involved in motion sickness (which is vestibular-driven), Metoclopramide is **ineffective** for this condition [1]. It is, however, useful for drug-induced vomiting or gastroparesis [1]. **Analysis of other options:** * **Scopolamine (Hyoscine):** An anticholinergic (M1 blocker). It is considered the **most effective drug** for motion sickness, especially when used as a transdermal patch for prophylaxis [2]. * **Cinnarizine:** A H1-antihistamine with additional calcium channel blocking activity. It is widely used for motion sickness and vertigo (labyrinthine sedative) [1]. * **Cyclizine:** A sedating H1-antihistamine with anticholinergic properties, commonly used for motion sickness [1]. **High-Yield NEET-PG Pearls:** * **Drug of Choice (Prophylaxis):** Scopolamine (apply 4 hours before the journey). * **Drug of Choice (Treatment/Short journey):** Promethazine or Cyclizine. * **Morning Sickness (Pregnancy):** Doxylamine + Pyridoxine (Vitamin B6). * **Chemotherapy-Induced Nausea (CINV):** Ondansetron (5-HT3 antagonist) is the mainstay. * **Key Concept:** Antihistamines used in motion sickness must cross the Blood-Brain Barrier (BBB); therefore, **second-generation antihistamines** (e.g., Cetirizine) are **ineffective** [3].

Question 147: Which among the following is a H2 receptor blocker?

A. Cimetidine (Correct Answer)
B. Cetirizine
C. Pyrilamine
D. Atropine

Explanation: ### Explanation **Correct Option: A. Cimetidine** **Mechanism of Action:** Histamine acts on **H2 receptors** located on the basolateral membrane of gastric parietal cells to stimulate acid secretion via the cAMP pathway. **Cimetidine** is a competitive antagonist at these H2 receptors. By blocking the action of histamine, it significantly reduces both basal and meal-stimulated gastric acid secretion, making it a classic treatment for peptic ulcer disease and GERD. **Analysis of Incorrect Options:** * **B. Cetirizine:** This is a **second-generation H1 receptor antagonist**. It is used primarily for allergic conditions (rhinitis, urticaria) and is preferred over first-generation drugs because it is non-sedating and does not cross the blood-brain barrier significantly. * **C. Pyrilamine (Mepyramine):** This is a **first-generation H1 receptor antagonist**. It is used for allergic reactions but possesses significant sedative and anticholinergic side effects. * **D. Atropine:** This is a **muscarinic (M) receptor antagonist**. While it can reduce gastric secretions by blocking M3 receptors on parietal cells, it is not an H2 blocker and is rarely used for acid suppression due to systemic side effects (tachycardia, dry mouth, blurred vision). **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Inhibition:** Cimetidine is a potent **Cytochrome P450 inhibitor**. It can increase the levels of drugs like Warfarin, Phenytoin, and Theophylline (Drug-Drug Interactions). * **Anti-androgenic Effects:** Cimetidine can cause **gynecomastia**, loss of libido, and impotence because it inhibits the binding of dihydrotestosterone to androgen receptors and increases prolactin levels. * **Other H2 Blockers:** Ranitidine, Famotidine (most potent), and Nizatidine. Unlike Cimetidine, these newer agents have minimal anti-androgenic effects and fewer drug interactions.

Question 148: Prolonged intake of proton pump inhibitors (PPIs) is associated with an increased risk of which of the following conditions?

A. Hypothyroidism
B. Pneumonia (Correct Answer)
C. Hepatitis
D. Pancreatitis

Explanation: **Explanation:** The correct answer is **Pneumonia (Option B)**. **Mechanism:** Proton pump inhibitors (PPIs) like Omeprazole irreversibly inhibit the H+/K+ ATPase pump, significantly increasing gastric pH. Under normal physiological conditions, gastric acid acts as a sterile barrier, killing ingested pathogens. When this "acid curtain" is removed, it leads to **gastric bacterial overgrowth**. These bacteria can migrate retrograde into the esophagus and be micro-aspirated into the respiratory tract, increasing the risk of community-acquired and nosocomial pneumonia. **Analysis of Incorrect Options:** * **A. Hypothyroidism:** PPIs do not directly cause hypothyroidism. However, they may *decrease* the absorption of levothyroxine (which requires an acidic medium), necessitating dose adjustments in hypothyroid patients. * **C. Hepatitis:** PPIs are metabolized by the liver (CYP2C19/3A4), but they are not typically hepatotoxic. In fact, they are frequently used in cirrhotic patients, though caution is advised regarding spontaneous bacterial peritonitis (SBP). * **D. Pancreatitis:** There is no established clinical link between prolonged PPI use and the development of pancreatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Other Long-term PPI Risks:** Chronic use is associated with **Hypomagnesemia**, **Vitamin B12 deficiency**, and **Osteoporosis** (due to decreased calcium carbonate absorption leading to increased fracture risk). * **Infections:** Beyond pneumonia, PPIs significantly increase the risk of ***Clostridioides difficile***-associated diarrhea and enteric infections (e.g., *Salmonella*, *Campylobacter*). * **Drug Interaction:** PPIs (especially Omeprazole) inhibit CYP2C19, which can decrease the activation of the antiplatelet drug **Clopidogrel**, potentially increasing the risk of cardiovascular events.

Question 149: Which of the following is an antidiarrheal combination drug that contains atropine and may be contraindicated in the treatment of diarrhea caused by intestinal organisms that may penetrate the gastrointestinal wall if transit time is excessively delayed?

A. Diphenoxylate (Correct Answer)
B. Sucralfate
C. Misoprostol
D. Metoclopramide

Explanation: **Explanation:** **Diphenoxylate** is a synthetic opioid derivative related to pethidine. It acts primarily on the $\mu$-opioid receptors in the GI tract to decrease intestinal motility (peristalsis) and increase transit time [3, 4]. In clinical practice, it is almost always combined with a sub-therapeutic dose of **Atropine** (Lomotil) to discourage abuse, as the atropine causes unpleasant anticholinergic side effects if taken in high doses. The contraindication mentioned refers to **Infective Diarrhea** (e.g., *Salmonella, Shigella, or C. difficile*). By slowing transit time, diphenoxylate allows these invasive organisms or their toxins to remain in contact with the intestinal mucosa for longer, potentially leading to systemic invasion, toxic megacolon, or worsening of the infection [3]. **Why other options are incorrect:** * **Sucralfate:** An ulcer-protective agent that forms a physical barrier over the ulcer base; it does not contain atropine or primarily treat diarrhea. * **Misoprostol:** A PGE1 analogue used for NSAID-induced ulcers and medical abortion. Its most common side effect is actually **diarrhea**, not its treatment. * **Metoclopramide:** A D2 receptor antagonist used as a **prokinetic** and antiemetic [1]. It increases GI motility, which would worsen diarrhea. **High-Yield NEET-PG Pearls:** * **Loperamide** is another opioid antidiarrheal; it is preferred over diphenoxylate because it does not cross the blood-brain barrier (no CNS effects) and has no abuse potential [3]. * **Specific Contraindication:** Antidiarrheals should be avoided in **Acute Ulcerative Colitis** as they can precipitate **Toxic Megacolon** [3]. * **Oral Rehydration Therapy (ORT)** remains the cornerstone of management for acute watery diarrhea.

Question 150: A patient presented with abdominal pain and frequent unsatisfactory bowel movements. For the last year, he has been using a purgative twice weekly to open his bowel. On colonoscopy, the colon was found to be atonic with bluish pigmentation of the mucosa. Which is the most likely purgative that the patient has been using?

A. Liquid paraffin
B. Lactulose
C. Ispaghula
D. Senna (Correct Answer)

Explanation: ### Explanation The clinical presentation described—chronic purgative use leading to an atonic colon and bluish-black pigmentation of the colonic mucosa—is a classic case of **Melanosis Coli**. **1. Why Senna is the correct answer:** Senna is an **Anthraquinone stimulant laxative**. Chronic use of anthraquinones (which also include Cascara and Aloe) leads to the accumulation of lipofuscin-laden macrophages in the lamina propria of the colonic mucosa. This results in a characteristic dark brown or bluish-black discoloration known as **Melanosis Coli**. Furthermore, long-term abuse of stimulant laxatives can damage the myenteric plexus, leading to a dilated, non-propulsive "cathartic colon" (atonic colon). **2. Why the other options are incorrect:** * **Liquid Paraffin (Option A):** A lubricant/stool softener. Its chronic use is associated with the malabsorption of fat-soluble vitamins (A, D, E, K) and lipid pneumonia if aspirated, but not mucosal pigmentation. * **Lactulose (Option B):** An osmotic laxative. It works by retaining water in the intestinal lumen. It does not cause structural changes or pigmentation of the colonic wall. * **Ispaghula (Option C):** A bulk-forming laxative. These are generally the safest for long-term use as they mimic dietary fiber and do not cause atonicity or melanosis. **Clinical Pearls for NEET-PG:** * **Melanosis Coli** is a benign, reversible condition; the pigmentation usually disappears within 4-12 months after discontinuing the anthraquinone laxative. * **Stimulant Laxatives** (e.g., Bisacodyl, Senna) are the most commonly abused class of purgatives. * **Cathartic Colon:** Characterized by the loss of haustral markings on imaging, often mimicking chronic ulcerative colitis ("stove-pipe appearance").

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

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Pancreatic Enzyme Supplements

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