Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 111: Which of the following proton pump inhibitors has enzyme inhibitory activity?

A. Rabeprazole
B. Lansoprazole
C. Pantoprazole
D. Omeprazole (Correct Answer)

Explanation: **Explanation:** **1. Why Omeprazole is the Correct Answer:** Omeprazole is a potent inhibitor of the hepatic microsomal enzyme system, specifically **CYP2C19** and **CYP3A4**. By inhibiting these enzymes, it reduces the metabolism of several drugs, leading to increased plasma concentrations and potential toxicity. This is a classic pharmacological property of the first-generation PPI, Omeprazole, which distinguishes it from newer agents in the class. **2. Why the Other Options are Incorrect:** * **Pantoprazole:** Known for having the **least potential** for drug-drug interactions. It has lower affinity for cytochrome P450 enzymes, making it the preferred PPI for patients on multiple medications (polypharmacy). * **Rabeprazole:** Primarily metabolized via a non-enzymatic pathway (reduction) with minor CYP involvement, resulting in minimal enzyme inhibition. * **Lansoprazole:** While it is metabolized by CYP enzymes, its inhibitory effect on the metabolism of other drugs is clinically insignificant compared to Omeprazole. **3. High-Yield Clinical Pearls for NEET-PG:** * **The Clopidogrel Interaction:** This is the most high-yield clinical application. Clopidogrel is a prodrug activated by **CYP2C19**. Because Omeprazole inhibits this enzyme, it prevents the activation of Clopidogrel, potentially increasing the risk of cardiovascular events (thrombosis). * **Other Interactions:** Omeprazole increases the half-life of **Warfarin, Phenytoin, and Diazepam**. * **Mechanism of Action:** All PPIs are prodrugs that irreversibly inhibit the **H+/K+ ATPase pump** (proton pump) in gastric parietal cells. * **Fastest Acting PPI:** Rabeprazole is often cited as having the fastest onset of action among the group.

Question 112: What is the drug of choice for late cisplatin-induced vomiting?

A. Omeprazole
B. Granisetron
C. Aprepitant (Correct Answer)
D. Dexamethasone

Explanation: **Explanation:** Cisplatin-induced emesis occurs in two distinct phases: **Acute** (within 24 hours) and **Delayed/Late** (24–72 hours). Understanding the neurotransmitters involved is key to selecting the correct therapy. 1. **Why Aprepitant is correct:** The delayed phase of vomiting is primarily mediated by **Substance P** acting on **Neurokinin-1 (NK1) receptors** in the solitary tract nucleus. **Aprepitant** is a selective NK1 receptor antagonist. It is specifically indicated for the prevention of delayed emesis because 5-HT3 antagonists (like Granisetron) lose their efficacy after the first 24 hours. 2. **Why other options are incorrect:** * **Granisetron:** This is a 5-HT3 receptor antagonist. While it is the drug of choice for **acute** cisplatin-induced vomiting, it is significantly less effective for the delayed phase. * **Dexamethasone:** While often used as an adjuvant to enhance the efficacy of both 5-HT3 and NK1 antagonists, it is not the primary drug of choice for the late phase when used alone. * **Omeprazole:** This is a Proton Pump Inhibitor (PPI) used for peptic ulcers and GERD; it has no anti-emetic properties. **High-Yield Clinical Pearls for NEET-PG:** * **Acute Emesis (<24h):** Mediated by Serotonin (5-HT3). DOC: **Ondansetron/Granisetron.** * **Delayed Emesis (>24h):** Mediated by Substance P (NK1). DOC: **Aprepitant/Rolapitant.** * **Anticipatory Emesis:** Triggered by psychological factors/sights/smells. DOC: **Lorazepam (Benzodiazepines).** * **Palonosetron:** A second-generation 5-HT3 antagonist with a long half-life that has some efficacy in both acute and delayed phases.

Question 113: Which of the following pharmacologic agents is not used in the management of Crohn's disease?

A. Infliximab
B. Adalimumab
C. Ustekinumab (Correct Answer)
D. Natalizumab

Explanation: ### Explanation The question asks to identify the agent **not** used in Crohn’s disease. However, based on current clinical guidelines and pharmacological standards (including Harrison’s and K.D. Tripathi), there appears to be a discrepancy in the provided options. **Ustekinumab is, in fact, FDA-approved and widely used for Crohn’s disease.** #### 1. Why the Correct Answer (Ustekinumab) is technically used: **Ustekinumab** is a monoclonal antibody that targets the **p40 subunit of IL-12 and IL-23**. It is highly effective and approved for patients with moderate-to-severe Crohn’s disease who have failed traditional TNF-inhibitor therapy. *Note: In older question banks, Ustekinumab was sometimes the "correct" answer because it was the newest drug and not yet included in older textbooks. For NEET-PG, if all four options are technically used, look for the drug with the most restricted use or highest toxicity.* #### 2. Analysis of Other Options: * **Infliximab (Option A):** A chimeric monoclonal antibody against **TNF-α**. It is a first-line biological agent for inducing and maintaining remission in Crohn’s, especially in fistulizing disease. * **Adalimumab (Option B):** A fully human monoclonal antibody against **TNF-α**. It is used similarly to Infliximab but administered subcutaneously. * **Natalizumab (Option C):** An anti-integrin antibody (targets **α4-integrin**). While effective for Crohn’s, its use is severely restricted due to the risk of **Progressive Multifocal Leukoencephalopathy (PML)** caused by JC virus reactivation. #### 3. High-Yield Clinical Pearls for NEET-PG: * **Vedolizumab:** A gut-selective anti-integrin (**α4β7**) used in IBD; it has a lower risk of PML compared to Natalizumab. * **Drug of Choice for Perianal/Fistulizing Crohn’s:** Infliximab. * **Step-up Therapy:** Starts with 5-ASA (Sulfasalazine/Mesalamine) or Budesonide, progressing to Azathioprine/6-MP, and finally Biologics. * **Key Difference:** Crohn's disease can involve any part of the GIT (skip lesions), whereas Ulcerative Colitis is confined to the colon (continuous involvement).

Question 114: Which of the following drugs is NOT used for paralytic ileus following bowel resection surgery?

A. Alvinopam
B. Dihydroergotamine
C. Naloxone (Correct Answer)
D. Methylnaltrexone

Explanation: ### Explanation **Correct Answer: C. Naloxone** **Concept:** Postoperative ileus (POI) is often exacerbated by the use of opioid analgesics, which activate **mu-opioid receptors** in the enteric nervous system, inhibiting gastric emptying and intestinal motility. To treat this, we use **Peripherally Acting Mu-Opioid Receptor Antagonists (PAMORAs)**. **Why Naloxone is the correct answer:** Naloxone is a non-selective opioid antagonist that readily crosses the **blood-brain barrier (BBB)**. If administered to treat postoperative ileus, it would reverse the central analgesic effects of opioids, causing the patient to experience severe postoperative pain. Therefore, it is not used for this indication. **Analysis of Incorrect Options:** * **A. Alvimopan:** This is a potent PAMORA specifically FDA-approved to accelerate the recovery of bowel function after small or large bowel resection. It does not cross the BBB, so it treats ileus without affecting pain control. * **B. Dihydroergotamine:** While primarily known for migraines, certain ergot alkaloids have historically been used for their prokinetic effects on the smooth muscle of the gut to treat paralytic ileus (though PAMORAs are now preferred). * **D. Methylnaltrexone:** This is a quaternary ammonium derivative of naltrexone. Due to its polar nature, it does not cross the BBB. It is used to treat opioid-induced constipation and postoperative ileus without reversing systemic analgesia. **High-Yield Clinical Pearls for NEET-PG:** * **PAMORAs:** Alvimopan, Methylnaltrexone, and Naloxegol. * **Key Distinction:** PAMORAs treat peripheral side effects (constipation/ileus) without causing withdrawal or reversing analgesia because they lack CNS penetration. * **Drug of Choice:** **Alvimopan** is specifically indicated for postoperative ileus, whereas **Methylnaltrexone** is more commonly used for opioid-induced constipation in palliative care. * **Neostigmine:** Another prokinetic used for acute colonic pseudo-obstruction (Ogilvie’s syndrome), but it carries a risk of bradycardia.

Question 115: A patient is diagnosed with Zollinger-Ellison syndrome. Which of the following would be the most appropriate pharmacotherapy?

A. Erythropoietin
B. Famotidine
C. Fluorouracil
D. Omeprazole (Correct Answer)

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. **1. Why Omeprazole is correct:** Proton Pump Inhibitors (PPIs) like **Omeprazole** are the drugs of choice for ZES [1]. They irreversibly inhibit the $H^+/K^+$-ATPase pump in gastric parietal cells, which is the final common pathway of acid secretion [1]. Because PPIs can achieve near-total suppression of acid regardless of the stimulus (gastrin, histamine, or acetylcholine), they are effective even against the extreme hypergastrinemia seen in ZES [1]. High doses are typically required initially. **2. Why the other options are incorrect:** * **Famotidine:** This is an $H_2$ receptor antagonist. While it reduces acid, it is significantly less potent than PPIs and cannot adequately control the massive acid output triggered by gastrinomas. * **Fluorouracil (5-FU):** This is a cytotoxic antimetabolite used in cancer chemotherapy. While ZES involves a tumor, the primary management of symptoms and mucosal damage relies on acid suppression, not 5-FU. * **Erythropoietin:** This is a hormone that stimulates red blood cell production; it has no role in acid-peptic disease. **Clinical Pearls for NEET-PG:** * **Diagnosis:** ZES is suspected when fasting serum gastrin levels are >1000 pg/mL. The **Secretin Stimulation Test** is the most specific provocative test (Secretin causes a paradoxical *increase* in gastrin in ZES patients). * **MEN-1 Association:** Approximately 25% of ZES cases occur as part of Multiple Endocrine Menaplasia Type 1 (3Ps: Parathyroid, Pancreas, Pituitary). * **Drug of Choice:** PPIs are the DOC for ZES, NSAID-induced ulcers, and H. pylori-associated peptic ulcer disease [1].

Question 116: All of the following are effective against cytotoxic drug-induced emesis except?

A. Dexamethasone
B. Hyoscine (Correct Answer)
C. Metoclopramide
D. Ondansetron

Explanation: **Explanation:** The management of chemotherapy-induced nausea and vomiting (CINV) targets specific neurotransmitter pathways in the **Chemoreceptor Trigger Zone (CTZ)** and the **Vagal afferents** in the GI tract. **Why Hyoscine is the correct answer:** Hyoscine (Scopolamine) is an anticholinergic drug that primarily acts on the vestibular system (M1 receptors). It is the drug of choice for **motion sickness** and vertigo but has **no significant efficacy** against cytotoxic drug-induced emesis. CINV is primarily mediated by serotonin (5-HT3), dopamine (D2), and substance P (NK1), rather than the vestibular-cholinergic pathway. **Analysis of other options:** * **Ondansetron:** A 5-HT3 receptor antagonist. It is the first-line agent for preventing acute CINV by blocking serotonin receptors on vagal afferents and the CTZ. * **Dexamethasone:** A corticosteroid that is highly effective against CINV, especially when used in combination with 5-HT3 antagonists. Its mechanism involves reducing peritumoral inflammation and prostaglandin synthesis. * **Metoclopramide:** A D2 receptor antagonist. In high doses, it also possesses 5-HT3 antagonistic activity, making it effective against cisplatin-induced emesis (though now largely superseded by newer agents). **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of choice for Motion Sickness:** Hyoscine (administered as a transdermal patch behind the ear). 2. **Drug of choice for CINV (Acute):** Ondansetron (5-HT3 antagonist). 3. **Drug of choice for Delayed CINV:** Aprepitant (NK1 receptor antagonist). 4. **Drug of choice for Morning Sickness (Pregnancy):** Doxylamine + Pyridoxine. 5. **Metoclopramide Side Effect:** Can cause Extrapyramidal Symptoms (EPS) like acute dystonia due to central D2 blockade.

Question 117: What is the antibiotic of choice in a cirrhotic patient to prevent hepatic encephalopathy?

A. Neomycin
B. Ampicillin
C. Metronidazole
D. Rifaximin (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Rifaximin** **Mechanism and Rationale:** Hepatic encephalopathy (HE) is primarily caused by the accumulation of neurotoxic ammonia, produced by urea-splitting bacteria in the gut. **Rifaximin** is a semi-synthetic, non-absorbable derivative of Rifampin. It acts locally in the gastrointestinal tract to inhibit bacterial RNA synthesis, thereby reducing the population of ammonia-producing enteric flora. Because it has minimal systemic absorption (<0.4%), it offers a superior safety profile with fewer systemic side effects, making it the current **drug of choice** for the prevention of recurrent HE episodes. **Analysis of Incorrect Options:** * **A. Neomycin:** Historically used to decrease ammonia-producing bacteria. However, it is no longer the first choice due to risks of **ototoxicity and nephrotoxicity**, even with minimal absorption, especially in patients with renal impairment. * **B. Ampicillin:** While it can alter gut flora, it is not specific for HE and carries a high risk of developing antibiotic resistance and *Clostridioides difficile* infection. * **C. Metronidazole:** Effective against anaerobes that produce ammonia, but long-term use is limited by the significant risk of **peripheral neuropathy**. **NEET-PG High-Yield Pearls:** * **First-line treatment for acute HE:** Lactulose (a non-absorbable disaccharide that traps ammonia as ammonium ions [$NH_4^+$] by acidifying the colon). * **Rifaximin's Role:** Primarily used as an add-on therapy to Lactulose for the prevention of recurrence. * **Mechanism of Rifaximin:** Binds to the beta-subunit of bacterial DNA-dependent RNA polymerase. * **Clinical Advantage:** Unlike Neomycin, Rifaximin does not require dosage adjustment in renal failure and has a lower potential for drug-drug interactions.

Question 118: What is not a rationale for sucralfate therapy in peptic ulcers?

A. It has an acid neutralizing action. (Correct Answer)
B. It inhibits pepsin mediated protein hydrolysis.
C. It stimulates the production of epidermal growth factor.
D. It stimulates prostaglandin synthesis.

Explanation: **Explanation:** Sucralfate is a complex of **aluminum hydroxide and sulfated sucrose**. Its primary mechanism of action is physical rather than chemical, making it a "cytoprotective" agent rather than an antacid. **1. Why Option A is the correct answer:** Sucralfate **does not have a significant acid-neutralizing capacity**. Unlike antacids (like Magnesium or Aluminum hydroxide), sucralfate requires an **acidic environment (pH < 4)** to be activated. In acidic medium, it polymerizes into a sticky, viscous paste that binds selectively to the base of the ulcer crater. Therefore, claiming it neutralizes acid is pharmacologically incorrect. **2. Why the other options are incorrect (Mechanisms of Sucralfate):** * **Option B:** The negatively charged sucrose sulfate binds to positively charged proteins (albumin, fibrinogen) in the ulcer base, forming a physical barrier that **prevents degradation by pepsin** and bile salts. * **Option C:** Sucralfate binds to **Epidermal Growth Factor (EGF)** and fibroblast growth factor, concentrating them at the ulcer site to promote mucosal regeneration and healing. * **Option D:** It stimulates the local release of **Prostaglandins (PGE2 and PGI2)** and nitric oxide, which increases mucosal blood flow and bicarbonate secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Administration:** It must be taken on an **empty stomach** (1 hour before meals). * **Drug Interactions:** Since it requires low pH for activation, it should **not** be given simultaneously with **Antacids, H2 blockers, or PPIs** (maintain a gap of 30–60 mins). * **Side Effects:** The most common side effect is **constipation** (due to the aluminum content). * **Hypophosphatemia:** It can bind to dietary phosphates, potentially leading to low phosphate levels in chronic use.

Question 119: Which of the following prokinetic drugs has been implicated in causing serious ventricular arrhythmias, particularly in patients concurrently receiving erythromycin or ketoconazole?

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

Explanation: **Explanation:** **Cisapride** is the correct answer because it is a substituted benzamide prokinetic that acts as a potent **5-HT₄ receptor agonist**. Its clinical use has been severely restricted or withdrawn in many countries due to its potential to cause **QT interval prolongation** and life-threatening ventricular arrhythmias, specifically **Torsades de Pointes**. The underlying mechanism involves the blockade of **HERG (human ether-a-go-go-related gene) potassium channels** in the heart, which delays repolarization. Cisapride is metabolized primarily by the **CYP3A4** enzyme. Therefore, concurrent administration of CYP3A4 inhibitors like **erythromycin** (macrolide) or **ketoconazole** (azole antifungal) leads to toxic plasma levels of Cisapride, significantly increasing the risk of fatal arrhythmias. **Analysis of Incorrect Options:** * **Domperidone (A):** While it can cause QT prolongation at high doses, it is a peripheral D₂ antagonist and does not carry the same high-risk profile for drug-drug interactions as Cisapride. * **Mosapride (C):** A newer 5-HT₄ agonist that is considered safer because it lacks significant affinity for the HERG potassium channels, thus carrying a lower risk of arrhythmias. * **Metoclopramide (D):** A D₂ antagonist and 5-HT₄ agonist. Its primary side effects are extrapyramidal (dystonias, Parkinsonism) due to central D₂ blockade, not cardiac arrhythmias. **High-Yield Pearls for NEET-PG:** * **Drug of Choice (DOC):** Metoclopramide is often the DOC for diabetic gastroparesis but is contraindicated in pheochromocytoma. * **Prucalopride:** A highly selective 5-HT₄ agonist used for chronic constipation with a superior cardiac safety profile. * **Erythromycin:** Acts as a prokinetic by stimulating **motilin receptors**, but its use is limited by tachyphylaxis.

Question 120: Which of the following statements regarding H2 receptor antagonists is FALSE?

A. They produce a dose-dependent inhibition of gastric acid secretion elicited by histamine.
B. They reduce the volume as well as H+ ion concentration of gastric juice.
C. They consistently lower the esophageal sphincter pressure. (Correct Answer)
D. They also reduce the secretion of intrinsic factor.

Explanation: **Explanation:** **Why Option C is the Correct (False) Statement:** H2 receptor antagonists (H2RAs) like Ranitidine and Famotidine primarily act on the parietal cells of the stomach. They have **no significant effect on the Lower Esophageal Sphincter (LES) pressure**. In clinical practice, drugs that decrease LES pressure (like Calcium Channel Blockers or Nitrates) can actually worsen Gastroesophageal Reflux Disease (GERD). Since H2RAs are used to treat GERD, they would be counterproductive if they lowered LES pressure. **Analysis of Other Options:** * **Option A:** H2RAs are competitive antagonists. They produce a **dose-dependent inhibition** of gastric acid secretion, especially effective against basal (nocturnal) acid secretion stimulated by histamine. * **Option B:** These drugs effectively reduce both the **total volume** of gastric juice and the **concentration of Hydrogen ions** (acidity). They also indirectly reduce pepsin secretion. * **Option D:** Intrinsic factor is secreted by the same parietal cells that secrete HCl. While H2RAs do reduce the secretion of intrinsic factor, this is rarely clinically significant in short-term use because the body has large stores of Vitamin B12. **NEET-PG High-Yield Pearls:** * **Cimetidine Specifics:** It is a potent **P450 enzyme inhibitor** and has **anti-androgenic effects** (can cause gynecomastia and galactorrhea). * **Drug of Choice:** Proton Pump Inhibitors (PPIs) have largely replaced H2RAs for PUD and GERD due to superior efficacy and longer duration of action. * **Tolerance:** Unlike PPIs, H2RAs can exhibit **tachyphylaxis** (rapidly diminishing response) within 3-7 days of starting therapy.

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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