Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 161: Ondansetron acts by inhibiting which of the following receptors?

A. 5-HT1
B. 5-HT2
C. 5-HT3 (Correct Answer)
D. 5-HT4

Explanation: **Explanation:** **Ondansetron** is a potent, highly selective **5-HT3 receptor antagonist**. It is the prototype drug of the "setron" family, primarily used as a first-line agent for preventing chemotherapy-induced nausea and vomiting (CINV), radiation-induced emesis, and post-operative vomiting. **Why 5-HT3 is correct:** The 5-HT3 receptors are unique among serotonin receptors as they are **ligand-gated ion channels** (not G-protein coupled). They are located peripherally on vagal nerve terminals in the gastrointestinal tract and centrally in the **Chemoreceptor Trigger Zone (CTZ)** and the Nucleus Tractus Solitarius (NTS). By blocking these receptors, Ondansetron prevents the emetic signal from reaching the vomiting center in the medulla. **Why other options are incorrect:** * **5-HT1:** These receptors (specifically 5-HT1B/1D) are targets for **Triptans** (e.g., Sumatriptan) used in the treatment of acute migraine. * **5-HT2:** These receptors are involved in platelet aggregation and smooth muscle contraction. Antagonists like **Cyproheptadine** are used for serotonin syndrome and as appetite stimulants. * **5-HT4:** These are prokinetic receptors. Agonists like **Prucalopride** or **Metoclopramide** (weakly) stimulate GI motility to treat constipation or gastroparesis. **High-Yield NEET-PG Pearls:** * **Side Effects:** The most common side effects are **headache** and constipation. * **ECG Changes:** Ondansetron can cause **QT interval prolongation** (caution in patients with electrolyte imbalances). * **Ineffectiveness:** It is notably **ineffective** in treating motion sickness (which is mediated by H1 and M1 receptors). * **Drug of Choice:** It is the drug of choice for prophylaxis of CINV but is often combined with Dexamethasone and Aprepitant (NK1 antagonist) for highly emetogenic regimens.

Question 162: Lubiprostone is a:

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

Explanation: **Explanation:** **Lubiprostone** is a bicyclic fatty acid derivative used primarily in the treatment of chronic idiopathic constipation and Irritable Bowel Syndrome with constipation (IBS-C). **1. Why Option A is Correct:** Lubiprostone acts as a selective **Chloride Channel Activator**. Specifically, it targets and activates the **type 2 chloride channels (ClC-2)** located on the apical (luminal) membrane of the intestinal epithelial cells. * **Mechanism:** Activation of these channels leads to an efflux of chloride ions into the intestinal lumen. * **Effect:** To maintain electroneutrality and osmotic balance, sodium ions and water follow the chloride into the lumen. This increased intestinal fluid secretion softens the stool and enhances intestinal motility, facilitating bowel movements. **2. Why Other Options are Incorrect:** * **Option B (Inhibitor):** Inhibiting chloride channels (e.g., using Crofelemer) would decrease fluid secretion, which is a strategy used for treating diarrhea, not constipation. * **Options C & D (Sodium Channels):** While sodium transport is vital for intestinal function, Lubiprostone does not directly bind to or modulate sodium channels. Its effect on sodium is secondary to the primary activation of chloride channels. **Clinical Pearls for NEET-PG:** * **Indications:** Chronic Idiopathic Constipation (CIC), IBS-C (in women), and Opioid-Induced Constipation (OIC). * **Pharmacokinetics:** It acts locally in the gut with minimal systemic absorption, reducing the risk of systemic side effects. * **Common Side Effect:** **Nausea** is the most frequently reported adverse effect (often dose-dependent). * **Comparison:** Unlike Linaclotide (which increases cGMP), Lubiprostone acts directly on the ClC-2 channel.

Question 163: Which drug is used in the management of irritable bowel syndrome with constipation?

A. Lubiprostone (Correct Answer)
B. Loperamide
C. Alosetron
D. Clonidine

Explanation: **Explanation:** **Lubiprostone (Option A)** is the correct answer. It is a **locally acting chloride channel activator** (specifically targeting ClC-2 channels) located on the apical membrane of the gastrointestinal epithelium. By increasing chloride-rich intestinal fluid secretion, it softens the stool and enhances intestinal motility without altering serum electrolyte levels. It is FDA-approved for **Irritable Bowel Syndrome with Constipation (IBS-C)** in women and for chronic idiopathic constipation. **Analysis of Incorrect Options:** * **Loperamide (Option B):** An opioid agonist that acts on $\mu$-receptors in the gut to inhibit peristalsis. It is used to treat **IBS-Diarrhea (IBS-D)**; using it in IBS-C would worsen the condition. * **Alosetron (Option C):** A 5-$HT_3$ receptor antagonist that reduces GI motility and visceral pain. It is indicated only for severe **IBS-D** in women who have failed conventional therapy. * **Clonidine (Option D):** An $\alpha_2$-adrenergic agonist. While it can increase intestinal water absorption (sometimes used in diabetic diarrhea), it is not a standard treatment for IBS-C. **High-Yield Clinical Pearls for NEET-PG:** * **Linaclotide & Plecanatide:** Other first-line agents for IBS-C; they act as **Guanylate Cyclase-C (GC-C) agonists**, increasing cGMP to stimulate chloride and bicarbonate secretion. * **Tegaserod:** A 5-$HT_4$ partial agonist used for IBS-C, but its use is restricted due to cardiovascular side effects. * **Drug of Choice for IBS-D:** Loperamide (symptomatic) or Eluxadoline ($\mu$-opioid agonist). * **Rifaximin:** An antibiotic often used in IBS-D to reduce bloating and alter gut flora.

Question 164: Which one of the following is not an antacid?

A. Magnesium sulfate (Correct Answer)
B. Magaldrate
C. Magnesium carbonate
D. Magnesium phosphate

Explanation: **Explanation:** The primary function of an **antacid** is to neutralize gastric hydrochloric acid (HCl), thereby increasing the gastric pH [3]. To act as an antacid, a compound must be a weak base. **Why Magnesium sulfate is the correct answer:** **Magnesium sulfate ($MgSO_4$)** is a salt of a strong acid (sulfuric acid) and a strong base (magnesium hydroxide). It lacks the chemical property to neutralize gastric acid. Instead, it acts as an **osmotic purgative** (laxative) [2]. Because the sulfate ion is poorly absorbed, it draws water into the intestinal lumen by osmosis, increasing bolus volume and stimulating peristalsis [2]. It is also used intravenously for managing eclampsia. **Analysis of incorrect options:** * **Magaldrate (Option B):** This is a hydrated complex of aluminum and magnesium hydroxides [1]. It is a highly effective antacid that reacts rapidly with HCl and provides a sustained buffering effect [1]. * **Magnesium carbonate (Option C):** This is a traditional systemic antacid that reacts with HCl to form magnesium chloride, water, and carbon dioxide. * **Magnesium phosphate (Option D):** This is a less common but recognized antacid compound used to neutralize gastric acidity. **High-Yield Clinical Pearls for NEET-PG:** * **Magnesium salts** generally cause **diarrhea** (osmotic effect), while **Aluminum salts** cause **constipation** (smooth muscle relaxation) [1]. They are often combined to balance bowel effects [1]. * **Milk-alkali syndrome** is a risk associated with excessive intake of calcium carbonate and absorbable alkalis. * Antacids can interfere with the absorption of drugs like **Tetracyclines, Iron, and Fluoroquinolones** due to chelation or changes in gastric pH [3].

Question 165: Which drug is useful in hepatic encephalopathy?

A. Magnesium sulphate
B. Lactulose (Correct Answer)
C. Bisacodyl
D. Biphosphonates

Explanation: **Explanation:** **Lactulose** is the mainstay of treatment for hepatic encephalopathy (HE). It is a non-absorbable disaccharide that acts through two primary mechanisms to reduce blood ammonia levels: 1. **Acidification of the Colon:** Colonic bacteria ferment lactulose into lactic and acetic acids. This lowers the pH, converting diffusible ammonia ($NH_3$) into non-diffusible ammonium ions ($NH_4^+$). This "ammonia trapping" prevents its absorption into the systemic circulation. 2. **Osmotic Laxative Effect:** It increases osmotic pressure in the gut, promoting the excretion of nitrogenous waste products and bacteria before they can produce more ammonia. **Analysis of Incorrect Options:** * **Magnesium Sulphate:** While used as an osmotic purgative, it is primarily used in obstetrics (eclampsia) or for rapid bowel evacuation. In renal failure (common in advanced liver disease), it carries a risk of magnesium toxicity. * **Bisacodyl:** A stimulant laxative that acts on the colonic mucosa to increase peristalsis. It does not alter colonic pH or ammonia metabolism, making it ineffective for HE. * **Bisphosphonates:** These are bone resorption inhibitors used for osteoporosis and hypercalcemia; they have no role in gastrointestinal or hepatic pathology. **High-Yield Facts for NEET-PG:** * **First-line combination:** Lactulose is often combined with **Rifaximin** (a non-absorbable antibiotic) for superior results in HE. * **Goal of therapy:** To achieve 2–3 soft stools per day. * **Other drugs for HE:** Neomycin (decreases ammonia-producing bacteria) and L-Ornithine L-Aspartate (LOLA), which stimulates the urea cycle. * **Avoid:** Diuretics and sedatives, as they can precipitate or worsen HE.

Question 166: Which agent is primarily used for the healing of stress ulcers?

A. H2 blockers (Correct Answer)
B. Proton pump inhibitors
C. Antacids
D. Bismuth

Explanation: **Explanation:** **H2 Blockers (Option A)** are considered the drug of choice for the **prophylaxis and healing of stress-related mucosal damage (SRMD)** or stress ulcers. Stress ulcers typically occur in critically ill patients (e.g., those with severe burns, trauma, or sepsis) due to mucosal ischemia and back-diffusion of gastric acid. H2 blockers, such as Ranitidine or Famotidine, are preferred because they can be administered intravenously and have a proven track record in reducing the incidence of clinically significant gastrointestinal bleeding in ICU settings. **Why other options are incorrect:** * **Proton Pump Inhibitors (Option B):** While PPIs are more potent acid suppressors and are the gold standard for Peptic Ulcer Disease (PUD) and GERD, clinical trials have traditionally established H2 blockers as the primary agent for stress ulcer prophylaxis. However, PPIs are increasingly used off-label for this purpose. * **Antacids (Option C):** These neutralize existing acid but require frequent dosing (every 1-2 hours) via a nasogastric tube to be effective for stress ulcers, making them impractical and increasing the risk of aspiration pneumonia. * **Bismuth (Option D):** This is a mucosal protective agent used primarily in *H. pylori* eradication regimens and has no significant role in the management of acute stress ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Curling’s Ulcer:** Stress ulcer associated with severe **burns**. * **Cushing’s Ulcer:** Stress ulcer associated with **increased intracranial pressure** (vagal stimulation leads to hypersecretion of acid). * **Risk Factors:** The two strongest indications for stress ulcer prophylaxis in the ICU are **mechanical ventilation (>48 hours)** and **coagulopathy**. * **Adverse Effect:** Prolonged use of H2 blockers or PPIs in the ICU may increase the risk of **Nosocomial Pneumonia** (due to bacterial overgrowth in a less acidic stomach).

Question 167: Diarrhea is a side effect of which of the following drugs?

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

Explanation: Misoprostol is a synthetic prostaglandin $E_1$ ($PGE_1$) analog [1]. It is primarily used for the prevention of NSAID-induced gastric ulcers [1]. The correct answer is Misoprostol because diarrhea is its most common dose-limiting side effect (occurring in up to 30% of patients). Mechanism of Diarrhea: Misoprostol stimulates $EP_3$ receptors on intestinal mucosal cells, leading to increased secretion of electrolytes and water into the intestinal lumen. It also enhances intestinal motility through smooth muscle contraction, resulting in a prokinetic effect that manifests as diarrhea and abdominal cramping [4]. Analysis of Incorrect Options: * Omeprazole: A Proton Pump Inhibitor (PPI) [3]. While it can rarely cause diarrhea (associated with *C. difficile* infection due to hypochlorhydria), its most common side effects are headache and nausea. * Sucralfate: An aluminum salt of sulfated sucrose that forms a protective barrier over ulcers. Its most common side effect is constipation (due to the aluminum content), not diarrhea [2]. * Metoclopramide: A $D_2$ receptor antagonist used as a prokinetic. While it increases gastric emptying, its primary side effects are extrapyramidal symptoms (dystonia, parkinsonism) and hyperprolactinemia. High-Yield NEET-PG Pearls: * Misoprostol Contraindication: It is strictly contraindicated in pregnancy (Category X) as it causes uterine contractions and can lead to abortion [4]. * Clinical Use: It is used off-label for medical abortion (in combination with Mifepristone) and for the induction of labor/postpartum hemorrhage [4]. * NSAID Ulcers: While PPIs are now the preferred treatment, Misoprostol is the specific "mechanistic" drug for preventing NSAID-induced mucosal injury [1].

Question 168: Omeprazole acts by inhibiting which of the following?

A. Na+/K+-ATPase
B. Na+/K+-ATPase
C. Calcium channels
D. H+/K+-ATPase (Correct Answer)

Explanation: **Explanation:** **Omeprazole** is a Proton Pump Inhibitor (PPI) used as the first-line treatment for peptic ulcer disease and GERD. It acts by irreversibly inhibiting the **H+/K+-ATPase enzyme system** (the "proton pump") located on the apical membrane of gastric parietal cells. This enzyme represents the final common pathway for gastric acid secretion; by blocking it, PPIs effectively inhibit both basal and stimulated acid secretion regardless of the stimulus (histamine, gastrin, or acetylcholine). **Analysis of Options:** * **H+/K+-ATPase (Correct):** Omeprazole is a prodrug that requires an acidic environment to be converted into its active form (sulfenamide). It then forms a covalent disulfide bond with the H+/K+-ATPase, leading to long-lasting inhibition. * **Na+/K+-ATPase (Incorrect):** This pump is found in almost all animal cells and is responsible for maintaining resting membrane potential. It is the primary target of **Cardiac Glycosides** (e.g., Digoxin), not PPIs. * **Calcium channels (Incorrect):** These are targeted by Calcium Channel Blockers (CCBs) like Nifedipine or Verapamil, primarily used in hypertension and arrhythmias. **High-Yield Clinical Pearls for NEET-PG:** * **Administration:** PPIs should be taken **30–60 minutes before breakfast** because the number of H+/K+-ATPase units is maximal after a fast. * **Drug of Choice:** PPIs are the DOC for Zollinger-Ellison Syndrome and NSAID-induced ulcers. * **Adverse Effects:** Long-term use is associated with **Hypomagnesemia**, Vitamin B12 deficiency, and increased risk of *C. difficile* infections and osteoporotic fractures (due to decreased calcium absorption). * **Drug Interaction:** Omeprazole inhibits **CYP2C19**, which can decrease the activation of the antiplatelet drug **Clopidogrel**.

Question 169: Which of the following antiemetics has less sedation and is used in motion sickness and vertigo?

A. Cyproheptadine
B. Chlorpheniramine
C. Promethazine
D. Meclizine (Correct Answer)

Explanation: **Explanation** The correct answer is **Meclizine**. **1. Why Meclizine is Correct:** Meclizine is a first-generation H1-antihistamine with significant anticholinergic properties. It is specifically indicated for the prevention and treatment of **motion sickness** and the management of **vertigo** associated with vestibular disorders (like Meniere’s disease). * **Mechanism:** It acts on the vestibular apparatus and the nucleus tractus solitarius to inhibit the vomiting center. * **Sedation Profile:** Compared to other first-generation antihistamines like Promethazine, Meclizine is **less sedating** and has a longer duration of action (up to 24 hours), making it a preferred choice for travelers. **2. Analysis of Incorrect Options:** * **Cyproheptadine (A):** Primarily used as an appetite stimulant and for serotonin syndrome. While it has H1-blocking properties, it is not a first-line drug for motion sickness. * **Chlorpheniramine (B):** A potent antihistamine used mainly for allergic rhinitis and urticaria. It has minimal efficacy in treating vertigo or motion sickness compared to piperazine derivatives like Meclizine. * **Promethazine (C):** While highly effective for motion sickness and post-operative nausea, it is **highly sedating** (often used as a pre-anesthetic medication). The question specifically asks for a drug with *less* sedation. **3. High-Yield NEET-PG Pearls:** * **Drug of Choice (DOC) for Motion Sickness (Prophylaxis):** Hyoscine (Scopolamine) – administered via a transdermal patch 4 hours before the journey. * **Meclizine Category:** It belongs to the **Piperazine** class of antihistamines (along with Cinnarizine and Cyclizine). * **Cinnarizine:** Another high-yield drug for vertigo; it acts by inhibiting the influx of $Ca^{2+}$ ions from the endolymph into the vestibular sensory cells (labyrinthine suppressant). * **Side Effects:** All drugs in this category can cause dry mouth and blurred vision due to their anticholinergic (muscarinic) blockade.

Question 170: Which of the following drugs can cause pancreatitis?

A. Colchicine
B. L-asparaginase (Correct Answer)
C. Ciprofloxacin
D. Nalidixic acid

Explanation: **Explanation:** **L-asparaginase** is a chemotherapy agent primarily used in the treatment of Acute Lymphoblastic Leukemia (ALL). It works by depleting extracellular asparagine, which leukemic cells require for protein synthesis. **Acute pancreatitis** is a well-documented and serious side effect of L-asparaginase, occurring in approximately 5–10% of patients. The mechanism is attributed to the inhibition of protein synthesis within pancreatic acinar cells, leading to cellular injury and the premature activation of digestive enzymes. **Analysis of Incorrect Options:** * **Colchicine (A):** Primarily used for gout, its dose-limiting toxicity is gastrointestinal distress (diarrhea, vomiting) and bone marrow suppression, but it is not a recognized cause of pancreatitis. * **Ciprofloxacin (C) & Nalidixic acid (D):** These fluoroquinolones/quinolones are more commonly associated with tendon rupture, QT prolongation, and CNS side effects (seizures). While many drugs are rare idiosyncratic causes of pancreatitis, they are not classic high-yield associations like L-asparaginase. **High-Yield Clinical Pearls for NEET-PG:** * **Common Drug-Induced Pancreatitis (DIP) Mnemonic:** "**F-A-S-T**" (**F**urosemide, **A**zathioprine/Asparaginase, **S**ulfonamides/Steroids, **T**etracyclines/Thiazides). * **Other notable causes:** Valproate, Estrogens, Didanosine (NRTI), and 6-Mercaptopurine. * **L-asparaginase** is also uniquely associated with **hypofibrinogenemia** and **thrombosis** due to decreased synthesis of clotting factors and Antithrombin III.

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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