Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 21: Which of the following is NOT a clinical use of Metoclopramide?

A. Motion sickness (Correct Answer)
B. Chemotherapy-induced vomiting
C. As an antiemetic
D. All of the above are uses of Metoclopramide

Explanation: **Explanation:** Metoclopramide is a **D2 receptor antagonist** that also possesses 5-HT4 agonistic and weak 5-HT3 antagonistic properties. It acts both centrally in the Chemoreceptor Trigger Zone (CTZ) and peripherally as a prokinetic agent. **1. Why Option A is correct (Motion Sickness):** Motion sickness is primarily mediated by the **vestibular system**, where H1 (histamine) and M1 (muscarinic) receptors predominate. Metoclopramide has no significant antihistaminic or anticholinergic activity. Therefore, it is **ineffective** in treating motion sickness. Drugs of choice for motion sickness include Hyoscine (anticholinergic) or Promethazine (antihistaminic). **2. Why other options are incorrect:** * **Option B (Chemotherapy-induced vomiting):** Metoclopramide is used in high doses to treat chemotherapy-induced nausea and vomiting (CINV) because, at high concentrations, it blocks 5-HT3 receptors in the CTZ. However, it has largely been superseded by Ondansetron. * **Option C (As an antiemetic):** It is a potent antiemetic used for post-operative vomiting and vomiting associated with systemic diseases (uremia, radiation sickness) due to its D2 blockade in the CTZ. **Clinical Pearls for NEET-PG:** * **Prokinetic Action:** It increases lower esophageal sphincter (LES) tone and promotes gastric emptying, making it useful in **Diabetic Gastroparesis** and GERD. * **Side Effects:** Due to central D2 blockade, it can cause **Extrapyramidal Symptoms (EPS)** like acute dystonia and Parkinsonism. It also causes **Hyperprolactinemia** (leading to galactorrhea/gynecomastia). * **Contraindication:** It should never be used in cases of **mechanical intestinal obstruction** or pheochromocytoma.

Question 22: What is the primary function of infliximab in the management of Crohn's disease?

A. Inhibition of Tumor Necrosis Factor-alpha (TNF-α) (Correct Answer)
B. Inhibition of Interleukin-2 (IL-2)
C. Epidermal Growth Factor Receptor (EGFR) inhibition
D. Inhibition of Vascular Endothelial Growth Factor (VEGF)

Explanation: **Explanation:** **1. Why Option A is Correct:** Infliximab is a chimeric monoclonal antibody that binds with high affinity to both soluble and transmembrane forms of **Tumor Necrosis Factor-alpha (TNF-α)**. In Crohn’s disease, TNF-α is a key pro-inflammatory cytokine that drives the chronic transmural inflammation of the bowel. By neutralizing TNF-α, infliximab prevents it from binding to its receptors, thereby reducing mucosal inflammation and promoting the healing of fistulas. **2. Why Other Options are Incorrect:** * **Option B (IL-2 Inhibition):** Drugs like Basiliximab or Daclizumab inhibit IL-2 receptors. These are primarily used as immunosuppressants in organ transplantation, not as first-line biologics for Crohn's. * **Option C (EGFR Inhibition):** Drugs like Cetuximab and Erlotinib target EGFR. These are used in the treatment of various malignancies (e.g., colorectal cancer, NSCLC) but have no role in managing inflammatory bowel disease (IBD). * **Option D (VEGF Inhibition):** Bevacizumab is a VEGF inhibitor used to inhibit angiogenesis in cancers and age-related macular degeneration. It is not used for IBD. **3. NEET-PG High-Yield Clinical Pearls:** * **Route of Administration:** Infliximab is given via **Intravenous (IV)** infusion, whereas Adalimumab (another TNF-α inhibitor) is given subcutaneously. * **Pre-treatment Screening:** Before starting Infliximab, patients **must** be screened for **Latent Tuberculosis (TB)** using a TST or IGRA, as TNF-α inhibitors can cause reactivation of TB. * **Other Indications:** Infliximab is also used in Ulcerative Colitis, Rheumatoid Arthritis, and Psoriasis. * **Adverse Effect:** Formation of "Antidrug Antibodies" (ADAs) can lead to loss of clinical response over time.

Question 23: The therapeutic effect of sulfasalazine in ulcerative colitis is exerted by which mechanism?

A. Inhibitory action of the unabsorbed drug on the abnormal colonic flora.
B. Breakdown of the drug in the colon to release 5-aminosalicylic acid, which suppresses inflammation locally. (Correct Answer)
C. Release of sulfapyridine having antibacterial properties.
D. Systemic immunomodulatory action of the drug.

Explanation: **Explanation:** Sulfasalazine is a prodrug used primarily in the management of Inflammatory Bowel Disease (IBD). It consists of two components—**5-aminosalicylic acid (5-ASA/Mesalamine)** and **Sulfapyridine**—linked by a covalent **azo bond**. 1. **Mechanism of Action (Why B is correct):** Sulfasalazine is poorly absorbed in the small intestine. Upon reaching the colon, bacterial enzymes (**azoreductases**) cleave the azo bond. This releases **5-ASA**, which is the active therapeutic moiety. 5-ASA acts **locally** by inhibiting prostaglandin and leukotriene synthesis (via COX and LOX inhibition) and scavenging free radicals, thereby suppressing mucosal inflammation. 2. **Analysis of Incorrect Options:** * **Option A:** While the drug reaches the colon, its primary effect is anti-inflammatory, not an alteration of colonic flora. * **Option C:** Sulfapyridine is indeed released, but it serves only as a carrier to ensure 5-ASA reaches the colon. It is absorbed systemically and is responsible for most of the drug's **toxicity** (e.g., hypersensitivity, bone marrow suppression), not its therapeutic effect in UC. * **Option D:** The action is predominantly local (topical) on the colonic mucosa, not systemic immunomodulation. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** 5-ASA (Mesalamine) is the active part; Sulfapyridine is the "carrier" (and the "toxic" part). * **Side Effects:** Dose-related nausea, headache, and reversible **oligospermia** (caused by the sulfapyridine component). * **Supplementation:** Sulfasalazine interferes with folate absorption; always co-prescribe **Folic acid**. * **Newer Agents:** Drugs like **Olsalazine** (dimer of 5-ASA) and **Balsalazide** were developed to deliver 5-ASA to the colon without the sulfa-related side effects.

Question 24: Ondansetron is a potent:

A. Antiemetic (Correct Answer)
B. Anxiolytic
C. Analgesic
D. Antidepressant

Explanation: **Explanation:** **Ondansetron** is a highly potent and selective **5-HT₃ (Serotonin) receptor antagonist**. It acts both peripherally on vagal nerve terminals in the gastrointestinal tract and centrally in the Chemoreceptor Trigger Zone (CTZ). By blocking these receptors, it inhibits the initiation of the vomiting reflex, making it a first-line **Antiemetic** (Option A). It is particularly effective for preventing chemotherapy-induced nausea and vomiting (CINV), radiation-induced emesis, and post-operative nausea and vomiting (PONV). **Why other options are incorrect:** * **Anxiolytic (Option B):** Drugs like Benzodiazepines (e.g., Diazepam) or SSRIs are used to treat anxiety. While some 5-HT receptor modulators affect mood, Ondansetron lacks significant CNS effects on anxiety. * **Analgesic (Option C):** Ondansetron does not possess pain-relieving properties. Common analgesics include NSAIDs or Opioids. * **Antidepressant (Option D):** While serotonin is involved in depression, treatment requires increasing synaptic serotonin (e.g., SSRIs). Blocking 5-HT₃ receptors does not alleviate depressive symptoms. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Selective 5-HT₃ blockade. * **Drug of Choice:** For prophylaxis of CINV and PONV. * **Side Effects:** The most common side effect is **headache** and **constipation**. * **ECG Changes:** It can cause **QT interval prolongation**; caution is required in patients with electrolyte imbalances or congenital long QT syndrome. * **Metabolism:** It is primarily metabolized by the liver (CYP2D6); dose adjustment may be needed in severe hepatic impairment.

Question 25: Anthranol acts as a purgative due to which of the following mechanisms?

A. Irritant action (Correct Answer)
B. Bulk formation in the intestinal lumen
C. Osmotic action
D. Emollient effect

Explanation: ### Explanation **Correct Option: A. Irritant action** Anthranol (and its derivatives like Anthraquinones) belongs to the class of **Stimulant or Irritant Purgatives**. These drugs act primarily in the colon. Once ingested, they are hydrolyzed by colonic bacteria into active metabolites (like emodin) that directly irritate the intestinal mucosa. This irritation leads to two primary effects: 1. **Increased Peristalsis:** Direct stimulation of the myenteric plexus increases propulsive activity. 2. **Altered Electrolyte Transport:** They inhibit Na⁺/K⁺-ATPase and increase prostaglandin synthesis, leading to the accumulation of water and electrolytes in the lumen. **Analysis of Incorrect Options:** * **B. Bulk formation:** This is the mechanism for agents like **Psyllium (Isabgol)** and **Methylcellulose**. They absorb water, swell, and increase the volume of intestinal contents, which mechanically stimulates peristalsis. * **C. Osmotic action:** This is seen with **Magnesium salts (Milk of Magnesia)** and **Lactulose**. These agents are non-absorbable and draw water into the lumen via osmosis, softening the stool and distending the bowel. * **D. Emollient effect:** This refers to **Stool Softeners** like **Docusate** or **Liquid Paraffin**, which act as surfactants to allow water and lipids to penetrate the fecal mass. **High-Yield Clinical Pearls for NEET-PG:** * **Anthraquinone examples:** Senna, Cascara, and Aloe. * **Melanosis Coli:** Chronic use of anthraquinone purgatives can lead to a characteristic brownish-black pigmentation of the colonic mucosa. * **Latency:** These drugs typically take 6–12 hours to act because they must reach the colon and be activated by bacterial flora. * **Contraindication:** Stimulant purgatives should be avoided in undiagnosed abdominal pain or intestinal obstruction.

Question 26: Which drug is absolutely contraindicated in a pregnant lady suffering from peptic ulcer?

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

Explanation: ### Explanation **Correct Option: C. Misoprostol** **Why Misoprostol is the Correct Answer:** Misoprostol is a synthetic **Prostaglandin E1 (PGE1) analogue**. While it is effective in treating NSAID-induced peptic ulcers by increasing gastric mucus production and decreasing acid secretion, it is **absolutely contraindicated (FDA Pregnancy Category X)** in pregnant women. Misoprostol possesses potent **uterotonic properties**, causing strong uterine contractions and cervical ripening. These effects can lead to partial or complete **abortion**, premature labor, or fetal death. In clinical practice, it is actually used legally for medical termination of pregnancy (MTP) and induction of labor, making its use in a continuing pregnancy dangerous. **Why Other Options are Incorrect:** * **A. Omeprazole:** A Proton Pump Inhibitor (PPI). It is generally considered safe in pregnancy (Category C/B). While not the first-line choice, it is used when H2 blockers fail. * **B & D. Ranitidine and Famotidine:** These are H2-receptor antagonists. They are considered **safe** and are often the first-line pharmacological treatment for GERD or peptic ulcers in pregnancy if lifestyle modifications fail. They do not possess teratogenic or oxytocic properties. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC)** for GERD/Peptic Ulcer in pregnancy: **Sucralfate** (due to negligible systemic absorption) or **H2 blockers** (Ranitidine/Famotidine). * **Misoprostol Side Effects:** The most common side effect is **diarrhea** and abdominal cramps. * **Clinical Use:** Misoprostol is the DOC for **prevention of NSAID-induced ulcers** in non-pregnant patients and is used in the management of **Postpartum Hemorrhage (PPH)**. * **Teratogenicity:** If a pregnancy continues after misoprostol exposure, there is a risk of **Möbius syndrome** (congenital facial paralysis).

Question 27: Which of the following is NOT a component of standard triple therapy for H. pylori eradication?

A. Amoxicillin
B. Gentamicin (Correct Answer)
C. Clarithromycin
D. Metronidazole

Explanation: **Explanation:** The standard **Triple Therapy** for *H. pylori* eradication is the first-line regimen used to treat peptic ulcer disease associated with this bacterium. The goal is to combine acid suppression with potent antibiotics that can penetrate the gastric mucosa. **Why Gentamicin is the correct answer:** Gentamicin is an **Aminoglycoside**. These drugs are highly polar, poorly absorbed from the GI tract, and, most importantly, they are **not effective against anaerobes or microaerophilic organisms** like *H. pylori*. Furthermore, they require an alkaline environment and oxygen for uptake into bacteria, making them unsuitable for the acidic, microaerophilic environment of the stomach. **Analysis of other options:** * **Amoxicillin (Option A):** A penicillin that acts by inhibiting cell wall synthesis. It has low resistance rates and is a core component of the triple therapy. * **Clarithromycin (Option B):** A macrolide that inhibits protein synthesis (50S subunit). It is the most effective antibiotic against *H. pylori* but is susceptible to resistance. * **Metronidazole (Option D):** An imidazole used as a substitute for Amoxicillin in patients with penicillin allergy. It is effective against anaerobic/microaerophilic organisms. **NEET-PG High-Yield Pearls:** 1. **Standard Triple Therapy (7–14 days):** **CAP** – **C**larithromycin (500mg BD), **A**moxicillin (1g BD), and a **P**PI (Standard dose BD). 2. **Penicillin Allergy:** Replace Amoxicillin with **Metronidazole** (400mg BD). 3. **Quadruple Therapy:** Used if triple therapy fails or in areas of high clarithromycin resistance. It includes: **PPI + Bismuth subsalicylate + Metronidazole + Tetracycline.** 4. **Sequential Therapy:** 5 days of PPI + Amoxicillin, followed by 5 days of PPI + Clarithromycin + Tinidazole.

Question 28: Which of the following prokinetic drugs acts on motilin receptors?

A. Erythromycin (Correct Answer)
B. Metoclopramide
C. Loxiglumide
D. Cisapride

Explanation: **Explanation:** **Erythromycin** is the correct answer because it acts as a **motilin receptor agonist**. Motilin is a 22-amino acid peptide hormone secreted by M cells in the duodenum and jejunum that initiates the Migrating Motor Complex (MMC), stimulating gastrointestinal motility. Erythromycin mimics the effects of motilin by binding to its receptors on the smooth muscle of the stomach and small intestine, making it a potent prokinetic agent, especially useful in diabetic gastroparesis. **Analysis of Incorrect Options:** * **Metoclopramide:** This is a **D2 receptor antagonist** and a **5-HT4 agonist**. It increases gastric emptying and lower esophageal sphincter (LES) tone but does not act on motilin receptors. * **Loxiglumide:** This is a **CCK1 (Cholecystokinin) receptor antagonist**. It is primarily studied for its effects on irritable bowel syndrome (IBS) and slowing intestinal transit, rather than acting as a prokinetic via motilin. * **Cisapride:** This is a **selective 5-HT4 receptor agonist**. While it is a prokinetic, its use is severely restricted due to the risk of fatal cardiac arrhythmias (Torsades de Pointes) caused by QT interval prolongation. **NEET-PG High-Yield Pearls:** * **Clinical Use:** Erythromycin is the drug of choice for **Diabetic Gastroparesis** (acute phase) and is used to clear the stomach of blood before endoscopy in upper GI bleeds. * **Tachyphylaxis:** A major limitation of Erythromycin as a prokinetic is the rapid development of tolerance (tachyphylaxis) due to down-regulation of motilin receptors. * **Side Effect:** At higher doses, it causes significant abdominal cramping and diarrhea due to its potent stimulatory effect.

Question 29: Which drug is not effective against H. pylori?

A. Colloidal Bismuth
B. Metronidazole
C. Amoxicillin
D. Erythromycin (Correct Answer)

Explanation: **Explanation:** The eradication of *Helicobacter pylori* is essential for treating peptic ulcer disease and preventing recurrence. The standard treatment involves a combination of a Proton Pump Inhibitor (PPI) and specific antibiotics. **Why Erythromycin is the correct answer:** While Erythromycin is a macrolide antibiotic, it is **not effective** against *H. pylori* in vivo. Although it shows some activity in vitro, it is rapidly degraded by gastric acid, leading to poor bioavailability at the site of infection. Furthermore, it has a high incidence of gastrointestinal side effects (acting as a motilin agonist), making it unsuitable for this regimen. Instead, **Clarithromycin** is the macrolide of choice because it is more acid-stable and has superior tissue penetration. **Analysis of incorrect options:** * **Colloidal Bismuth (A):** Bismuth subsalicylate or subcitrate has direct bactericidal effects on *H. pylori*, prevents its adherence to the gastric mucosa, and inhibits its bacterial enzymes. It is a key component of "Bismuth-based Quadruple Therapy." * **Metronidazole (B):** This nitroimidazole is effective against anaerobic bacteria and *H. pylori*. It is often used in patients allergic to penicillin or in areas with low resistance. * **Amoxicillin (C):** A penicillin derivative that is highly effective against *H. pylori* with a very low rate of primary resistance. It acts by inhibiting bacterial cell wall synthesis. **High-Yield Clinical Pearls for NEET-PG:** * **First-line (Standard Triple Therapy):** PPI + Clarithromycin + Amoxicillin (or Metronidazole) for 10–14 days. * **Bismuth Quadruple Therapy:** PPI + Bismuth + Metronidazole + Tetracycline (Preferred in areas with high Clarithromycin resistance). * **Drug of Choice for H. pylori:** Clarithromycin is the most potent antibiotic in the regimen. * **Sequential Therapy:** Involves 5 days of PPI + Amoxicillin, followed by 5 days of PPI + Clarithromycin + Tinidazole.

Question 30: Anti emetic action is produced through which of the following mechanisms?

A. Decreased CTZ stimulation
B. H1 agonistic action
C. D1 antagonistic action
D. 5 HT4 agonistic action (Correct Answer)

Explanation: ### Explanation The control of vomiting involves a complex interplay of neurotransmitters in the **Chemoreceptor Trigger Zone (CTZ)**, the **Vomiting Center (VC)**, and the **Gastrointestinal (GI) tract**. **Why Option D is Correct:** **5-HT4 agonists** (e.g., Metoclopramide, Prucalopride, Tegaserod) act primarily as **prokinetic agents**. By stimulating 5-HT4 receptors on enteric cholinergic neurons, they increase the release of acetylcholine. This enhances gastric emptying and upper GI motility (prokinetic effect), which indirectly produces an anti-emetic effect by preventing gastric stasis and reducing upward pressure on the lower esophageal sphincter. **Analysis of Incorrect Options:** * **Option A (Decreased CTZ stimulation):** While reducing CTZ stimulation *is* an anti-emetic mechanism, the option is phrased as a physiological result rather than a specific pharmacological mechanism of a drug class. * **Option B (H1 agonistic action):** This is incorrect. **H1 antagonists** (e.g., Promethazine, Diphenhydramine) are used for motion sickness. An agonist would likely worsen symptoms or have no anti-emetic value. * **Option C (D1 antagonistic action):** Anti-emetics like Metoclopramide and Domperidone work via **D2 receptor antagonism**, not D1. D2 receptors in the CTZ are potent triggers for emesis. **High-Yield Clinical Pearls for NEET-PG:** * **Metoclopramide** is a "dual-action" anti-emetic: it is a **D2 antagonist** (central action) and a **5-HT4 agonist** (peripheral prokinetic action). It also has weak 5-HT3 antagonistic properties at high doses. * **Drug of Choice (DOC):** * **Chemotherapy-Induced Nausea and Vomiting (CINV):** 5-HT3 antagonists (Ondansetron). * **Motion Sickness:** Hyoscine (Anticholinergic) or H1 antihistamines. * **Post-operative Nausea and Vomiting (PONV):** Ondansetron. * **Side Effect Note:** D2 antagonists can cause **Extrapyramidal Symptoms (EPS)** due to dopamine blockade in the nigrostriatal pathway.

Practice by Chapter

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Prokinetic Agents

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Laxatives and Purging Agents

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Antidiarrheal Drugs

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