Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 131: Which of the following selectively acts on 5HT3 receptors?

A. Ondansetron (Correct Answer)
B. Bupropion
C. Sumatriptan
D. Renzapride

Explanation: **Explanation:** **Ondansetron** is the correct answer because it is a prototype **selective 5-HT3 receptor antagonist** [1], [3]. These receptors are ligand-gated ion channels located peripherally on vagal nerve terminals and centrally in the Chemoreceptor Trigger Zone (CTZ) [1]. By blocking these receptors, Ondansetron effectively inhibits the emetic reflex, making it the drug of choice for **Chemotherapy-Induced Nausea and Vomiting (CINV)** and post-operative vomiting [1], [3]. **Analysis of Incorrect Options:** * **Bupropion:** An atypical antidepressant that acts as a Norepinephrine-Dopamine Reuptake Inhibitor (NDRI). It is also used for smoking cessation but has no significant activity at 5-HT3 receptors. * **Sumatriptan:** A selective **5-HT1B/1D receptor agonist** used in the acute treatment of migraine to cause intracranial vasoconstriction. * **Renzapride:** A substituted benzamide that acts as a **5-HT4 receptor agonist** and a 5-HT3 antagonist. Unlike Ondansetron, it is not *selective* for 5-HT3 and is primarily studied for its prokinetic effects in IBS. **High-Yield Clinical Pearls for NEET-PG:** * **Side Effects:** The most common side effect of Ondansetron is **headache** and constipation. A critical ECG finding to remember is **QT interval prolongation**. * **Drug of Choice:** Ondansetron is the preferred agent for vomiting caused by radiotherapy and cytotoxic drugs (cisplatin), but it is **ineffective** in motion sickness (where H1 and M1 blockers are used) [1], [2]. * **Other 5-HT3 Antagonists:** Palonosetron (longest half-life) and Granisetron [1], [3].

Question 132: Fosaprepitant is used as:

A. Antidepressant
B. Antiemetic (Correct Answer)
C. Antihypertensive
D. Diuretic

Explanation: **Explanation:** **Fosaprepitant** is a water-soluble prodrug of **Aprepitant**. It belongs to the class of **Neurokinin-1 (NK1) receptor antagonists**. 1. **Why it is an Antiemetic:** The mechanism involves blocking the binding of **Substance P** to NK1 receptors located in the *area postrema* (Chemoreceptor Trigger Zone) and the nucleus tractus solitarius. It is specifically indicated for the prevention of both acute and delayed phases of **Chemotherapy-Induced Nausea and Vomiting (CINV)**, particularly with highly emetogenic drugs like Cisplatin. It is usually used in a "triple regimen" along with a 5-HT3 antagonist (e.g., Ondansetron) and a corticosteroid (e.g., Dexamethasone). 2. **Why other options are incorrect:** * **Antidepressant:** While Substance P was once researched for mood disorders, NK1 antagonists have not shown clinical efficacy as antidepressants. Common antidepressants include SSRIs or TCAs. * **Antihypertensive:** Fosaprepitant has no effect on peripheral vascular resistance or cardiac output. * **Diuretic:** It does not act on the nephrons to promote diuresis. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Fosaprepitant is administered **intravenously**, whereas Aprepitant is given orally. * **Metabolism:** It is a substrate, inducer, and inhibitor of **CYP3A4**. It can decrease the concentration of Warfarin (monitor INR) and increase the concentration of Dexamethasone (dose reduction of steroid is required). * **Other NK1 Antagonists:** Rolapitant and Netupitant (often combined with Palonosetron).

Question 133: Octreotide is useful in esophageal varices. It is a synthetic analogue of somatostatin. Which statement regarding this drug is true?

A. It can be given orally
B. It is longer acting than somatostatin (Correct Answer)
C. Its major adverse effect is secretory diarrhea
D. All of the above

Explanation: **Explanation:** **1. Why Option B is Correct:** Somatostatin is a natural hormone with an extremely short half-life (approximately 1–3 minutes), making it clinically impractical for continuous use without constant infusion. **Octreotide** is a synthetic octapeptide analogue designed to be more potent and significantly **longer-acting** (half-life of ~1.5 to 2 hours). This extended duration of action allows for subcutaneous or intravenous bolus administration. In esophageal varices, it works by causing selective splanchnic vasoconstriction, thereby reducing portal venous pressure and controlling bleeding. **2. Why Other Options are Incorrect:** * **Option A:** Octreotide is a peptide. Like insulin, it is degraded by gastric enzymes if taken orally. It must be administered parenterally (SC or IV). * **Option C:** Octreotide actually **inhibits** intestinal secretion and motility. Therefore, it is used to *treat* secretory diarrhea (e.g., in Carcinoid syndrome or VIPoma). Its major gastrointestinal side effects are actually **steatorrhea** (due to inhibition of pancreatic enzymes) and **gallstones/biliary sludge** (due to inhibition of gallbladder contraction). **3. NEET-PG High-Yield Pearls:** * **Mechanism in Varices:** It inhibits the release of glucagon and other vasodilator peptides, leading to indirect splanchnic vasoconstriction. * **Clinical Uses:** Acromegaly (inhibits GH), Secretory diarrheas (VIPoma, Carcinoid), and Acute variceal bleeding. * **Drug of Choice:** While Octreotide is commonly used, **Terlipressin** (a vasopressin analogue) is often considered the drug of choice for esophageal varices as it has been shown to improve survival rates. * **Side Effect Profile:** Long-term use carries a high risk of **cholelithiasis** (gallstones) in up to 25% of patients.

Question 134: Which of the following is not an antacid drug?

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

Explanation: **Explanation:** Antacids are basic substances that react with gastric hydrochloric acid to form salt and water, thereby increasing the pH of the gastric contents. **Why Magnesium Sulphate is the correct answer:** **Magnesium sulphate (Epsom salt)** is not an antacid; it is a **purgative (osmotic laxative)**. When taken orally, it is poorly absorbed and retains water in the intestinal lumen through osmosis, increasing fecal volume and stimulating peristalsis. In clinical practice, it is also used intravenously as the drug of choice for **eclampsia** and for managing certain arrhythmias like Torsades de Pointes. **Why the other options are incorrect:** * **Aluminium hydroxide:** A non-systemic antacid. It is slow-acting but has a long duration. A common side effect is **constipation**, which is why it is often combined with magnesium salts. * **Sodium bicarbonate:** A systemic antacid. It is highly soluble, acts rapidly, and can cause systemic alkalosis and "acid rebound." It is generally avoided for long-term peptic ulcer therapy. * **Calcium carbonate:** A potent antacid that acts quickly. However, it can cause hypercalcemia and "milk-alkali syndrome" if taken in large quantities. **High-Yield Clinical Pearls for NEET-PG:** * **Antacid Combinations:** Magnesium salts (cause diarrhea) and Aluminium salts (cause constipation) are frequently combined to neutralize their effects on bowel movements (e.g., Magaldrate). * **Drug Interactions:** Antacids can decrease the absorption of drugs like **Tetracyclines, Iron, and Fluoroquinolones** by forming insoluble complexes (chelation). * **Magnesium Trisilicate:** Unlike the sulphate, the trisilicate form *is* used as an antacid and has adsorbent properties.

Question 135: What is the drug of choice for ulcerative colitis?

A. Salazopyrine
B. Prednisolone
C. Mercaptopurine
D. 5-aminosalicylic acid (Correct Answer)

Explanation: **Explanation:** **1. Why 5-Aminosalicylic Acid (5-ASA) is Correct:** 5-ASA (Mesalamine) is the **drug of choice (DOC)** for both the induction of remission and the maintenance of remission in mild-to-moderate Ulcerative Colitis (UC) [2]. It acts locally on the colonic mucosa to inhibit the production of pro-inflammatory mediators (prostaglandins and leukotrienes) by inhibiting the lipoxygenase pathway [1]. Its efficacy is maximized when delivered directly to the site of inflammation [3]. **2. Why the other options are incorrect:** * **Salazopyrine (Sulfasalazine):** This is a prodrug consisting of 5-ASA linked to sulfapyridine. While effective, it is no longer the first-line choice because the sulfapyridine moiety causes significant systemic side effects (hypersensitivity, oligospermia, and headache). Pure 5-ASA preparations are preferred for better tolerability [1]. * **Prednisolone:** Corticosteroids are highly effective for **inducing remission** in acute exacerbations (moderate-to-severe cases), but they are **never** used for maintenance therapy due to their extensive long-term side effects. * **Mercaptopurine:** This is an immunosuppressant used for steroid-dependent or refractory cases. It has a slow onset of action (3–6 months), making it unsuitable for acute management. **3. Clinical Pearls for NEET-PG:** * **Site of Action:** 5-ASA is absorbed in the small intestine; therefore, specialized delivery systems (e.g., pH-dependent coatings like Eudragit or prodrugs like Balsalazide) are used to ensure the drug reaches the **colon** [3]. * **Topical vs. Oral:** For distal UC (proctitis), **topical 5-ASA (suppositories/enemas)** is more effective than oral therapy. * **Step-up Therapy:** If 5-ASA fails, the next steps are typically Corticosteroids → Thiopurines (Azathioprine) → Biologics (Infliximab). * **Sulfasalazine Supplementation:** Patients on Sulfasalazine must receive **Folic acid** supplementation as the drug inhibits its absorption.

Question 136: A patient on cisplatin therapy develops intractable vomiting on the third day of treatment. What is the agent of choice for controlling this vomiting?

A. Aprepitant (Correct Answer)
B. Ondansetron
C. Metoclopramide
D. Prochlorperazine

Explanation: ### Explanation The key to answering this question lies in distinguishing between **acute** and **delayed** chemotherapy-induced nausea and vomiting (CINV). **1. Why Aprepitant is Correct:** Cisplatin is a highly emetogenic drug. It causes vomiting in two phases: * **Acute phase (<24 hours):** Primarily mediated by **Serotonin (5-HT3)** release. * **Delayed phase (2–5 days):** Primarily mediated by **Substance P** acting on **Neurokinin-1 (NK1) receptors** in the area postrema. Since the patient is experiencing vomiting on the **third day**, it is classified as delayed emesis. **Aprepitant**, an NK1 receptor antagonist, is the drug of choice for the prevention and treatment of delayed CINV. **2. Why Other Options are Incorrect:** * **Ondansetron (5-HT3 antagonist):** While it is the gold standard for *acute* emesis, it has limited efficacy in the *delayed* phase (after 24 hours). * **Metoclopramide (D2 antagonist):** It was historically used in high doses for cisplatin, but it is less effective than 5-HT3 or NK1 antagonists and carries a risk of extrapyramidal side effects. * **Prochlorperazine (D2 antagonist):** This is a low-potency antipsychotic used for mild-to-moderate nausea (e.g., motion sickness or post-operative), but it is insufficient for highly emetogenic cisplatin-induced delayed emesis. ### High-Yield NEET-PG Pearls: * **Triple Therapy for Cisplatin:** The current recommendation for highly emetogenic chemotherapy is a combination of **NK1 antagonist (Aprepitant) + 5-HT3 antagonist (Ondansetron) + Dexamethasone.** * **Aprepitant Metabolism:** It is a substrate, inhibitor, and inducer of **CYP3A4**. * **Palonosetron:** A second-generation 5-HT3 antagonist with a longer half-life that has some efficacy in delayed emesis, but NK1 antagonists remain the primary choice.

Question 137: All of the following drugs are used in the management of hepatic encephalopathy except?

A. L-ornithine L-aspartate
B. Rifaximin
C. Lactulose
D. Phenobarbitone (Correct Answer)

Explanation: **Explanation:** The primary goal in managing **Hepatic Encephalopathy (HE)** is to reduce the production and absorption of ammonia ($NH_3$), which is neurotoxic. **Why Phenobarbitone is the correct answer:** **Phenobarbitone** is a barbiturate that acts as a Central Nervous System (CNS) depressant. In hepatic encephalopathy, the brain is already in a state of metabolic depression due to hyperammonemia and increased GABAergic tone. Administering Phenobarbitone would **worsen the altered sensorium** and could precipitate a coma. Furthermore, it is metabolized by the liver, which is already failing in these patients. (Note: Phenobarbitone is used in Crigler-Najjar syndrome type II to induce glucuronyltransferase, but not in HE). **Why the other options are used:** * **L-ornithine L-aspartate (LOLA):** These are substrates for the urea cycle and glutamine synthesis, helping to detoxify ammonia into urea and glutamine in the liver and muscles. * **Rifaximin:** A non-absorbable antibiotic that eliminates ammonia-producing bacteria in the gut. It is currently the preferred add-on therapy to lactulose. * **Lactulose:** A non-absorbable disaccharide that acts as an osmotic laxative. It is fermented by colonic bacteria into organic acids, lowering the pH (acidifying the gut). This converts absorbable $NH_3$ into non-absorbable $NH_4^+$ (Ammonia Trapping). **NEET-PG High-Yield Pearls:** * **First-line treatment:** Lactulose (aim for 2–3 soft stools/day). * **Drug of choice for prevention of recurrence:** Rifaximin. * **Neomycin:** Another antibiotic used, but limited by side effects like ototoxicity and nephrotoxicity. * **Flumazenil:** May be used transiently if benzodiazepine-like substances are suspected of worsening the encephalopathy.

Question 138: What is the most specific drug used for NSAID-induced peptic ulcer?

A. Misoprostol (Correct Answer)
B. Proton pump inhibitors
C. H2 blockers
D. Mucaine gel

Explanation: ### Explanation **Correct Answer: A. Misoprostol** **Mechanism and Rationale:** NSAIDs induce peptic ulcers primarily by inhibiting the enzyme **Cyclooxygenase-1 (COX-1)**, which leads to a deficiency of endogenous **Prostaglandins (PGE2 and PGI2)**. These prostaglandins are vital for gastric mucosal protection as they increase bicarbonate secretion, enhance mucus production, and maintain mucosal blood flow. **Misoprostol**, a synthetic **PGE1 analogue**, directly replaces these missing prostaglandins. It acts on EP3 receptors on parietal cells to inhibit acid secretion and provides a cytoprotective effect, making it the **most specific** pharmacological intervention to counteract the exact mechanism of NSAID-induced damage. **Analysis of Incorrect Options:** * **B. Proton Pump Inhibitors (PPIs):** While PPIs (e.g., Omeprazole) are currently the **drug of choice (DOC)** in clinical practice for both treatment and prophylaxis of NSAID-induced ulcers due to better tolerability, they are not the "most specific" in terms of reversing the underlying prostaglandin deficiency. * **C. H2 Blockers:** These are less effective than PPIs and Misoprostol in preventing NSAID-induced gastric ulcers, as they only address acid secretion and not mucosal defense. * **D. Mucaine Gel:** This is a combination of an antacid and a local anesthetic (Oxetacaine). It provides symptomatic relief but does not treat or prevent the underlying ulcer pathology. **High-Yield NEET-PG Pearls:** * **Drug of Choice (Clinical):** PPIs (due to fewer side effects). * **Most Specific Drug:** Misoprostol (replaces deficient prostaglandins). * **Key Side Effect of Misoprostol:** Diarrhea and abdominal cramps (most common). * **Contraindication:** Pregnancy, as it is an **abortifacient** (causes uterine contractions). It is also used for medical abortion and induction of labor.

Question 139: Which is the most common adverse drug reaction of acarbose?

A. Flatulence (Correct Answer)
B. Hypoglycemia
C. Periodic Hyperglycemia
D. Weight gain

Explanation: **Acarbose** is an **$\alpha$-glucosidase inhibitor** used in the management of Type 2 Diabetes Mellitus. Its mechanism involves inhibiting the enzyme $\alpha$-glucosidase at the brush border of the small intestine, which delays the digestion and absorption of complex carbohydrates (starch and sucrose) [1]. **Why Flatulence is the correct answer:** Because carbohydrate absorption is delayed, undigested carbohydrates reach the **colon**. Here, they undergo bacterial fermentation, leading to the production of gases (CO₂, H₂, and methane). This results in the most common side effects: **flatulence (seen in >70% of patients)**, abdominal bloating, and osmotic diarrhea [1]. **Analysis of Incorrect Options:** * **B. Hypoglycemia:** Acarbose does not stimulate insulin secretion (it is euglycemic). Therefore, it does not cause hypoglycemia when used as monotherapy [2]. * **C. Periodic Hyperglycemia:** Acarbose specifically targets **post-prandial hyperglycemia** by slowing glucose absorption; it does not cause rebound or periodic hyperglycemia. * **D. Weight gain:** Unlike sulfonylureas or insulin, acarbose is **weight-neutral** or may even cause modest weight loss, making it a preferred choice in obese diabetic patients. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment of Hypoglycemia:** If a patient on acarbose develops hypoglycemia (due to concurrent use of insulin or sulfonylureas), they must be treated with **pure glucose (dextrose)**, not sucrose (cane sugar), because acarbose prevents the breakdown of sucrose into glucose [2]. * **Contraindication:** It should be avoided in patients with **Inflammatory Bowel Disease (IBD)** or chronic intestinal disorders due to gas production.

Question 140: What is the drug of choice for Zollinger-Ellison syndrome?

A. Antihistamines
B. Proton pump inhibitors (Correct Answer)
C. Dopamine agonists
D. Antacids

Explanation: **Explanation:** **Zollinger-Ellison Syndrome (ZES)** is characterized by a gastrin-secreting tumor (gastrinoma), usually located in the pancreas or duodenum. This leads to massive hypersecretion of gastric acid, resulting in severe, recurrent peptic ulcers and diarrhea. **Why Proton Pump Inhibitors (PPIs) are the Correct Choice:** PPIs (e.g., Omeprazole, Pantoprazole) are the **drug of choice** because they inhibit the $H^+/K^+$-ATPase pump, the final common pathway of acid secretion. Unlike other drugs, PPIs can achieve near-total suppression of acid regardless of the stimulus (gastrin, histamine, or acetylcholine). In ZES, high doses of PPIs are required to control the extreme acid output and promote ulcer healing. **Analysis of Incorrect Options:** * **Antihistamines (H2 Blockers):** While drugs like Ranitidine can reduce acid, they are significantly less potent than PPIs. In ZES, the massive gastrin levels easily overcome H2 receptor blockade, making them ineffective for long-term management. * **Dopamine Agonists:** These (e.g., Bromocriptine) have no role in acid suppression. Dopamine *antagonists* (like Metoclopramide) are used as prokinetics, but not for ZES. * **Antacids:** These only neutralize existing acid and have a very short duration of action. They provide symptomatic relief but cannot manage the underlying hypersecretion in ZES. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** ZES is suspected when a patient has multiple ulcers in atypical locations (e.g., distal duodenum or jejunum). * **Screening:** The best initial test is a **fasting serum gastrin level** (>1000 pg/mL is diagnostic). * **MEN-1 Association:** Approximately 25% of ZES cases occur as part of Multiple Endocrine Neoplasia Type 1 (3 Ps: Parathyroid, Pancreas, Pituitary). * **Octreotide Scintigraphy:** This is the most sensitive imaging modality to localize the gastrinoma.

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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