Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases Indian Medical PG Practice Questions and MCQs

Question 251: All of the following statements about Aprepitant are true, except:

A. Agonist at Neurokinin receptor (NK1) (Correct Answer)
B. Crosses the blood brain barrier
C. Metabolized by Cytochrome P450 3A4 pathway
D. Ameliorates nausea and vomiting of chemotherapy

Explanation: **Explanation:** **Aprepitant** is a high-affinity **Neurokinin-1 (NK1) receptor antagonist**. It works by blocking the binding of **Substance P** (an endogenous neuropeptide) to NK1 receptors located in the Area Postrema and the Nucleus Tractus Solitarius. 1. **Why Option A is the correct answer (False statement):** Aprepitant is an **antagonist**, not an agonist. By blocking the NK1 receptor, it inhibits the emetic reflex triggered by Substance P. 2. **Why other options are incorrect (True statements):** * **Option B:** It is a highly lipophilic molecule that effectively **crosses the blood-brain barrier** to act on central NK1 receptors. * **Option C:** It is primarily **metabolized by the CYP3A4 pathway**. This is clinically significant as it can lead to drug-drug interactions (e.g., it may increase levels of dexamethasone or chemotherapy agents metabolized by the same enzyme). * **Option D:** It is highly effective in **ameliorating both acute and delayed nausea and vomiting** associated with highly emetogenic chemotherapy (HEC), such as Cisplatin. **High-Yield Clinical Pearls for NEET-PG:** * **Triple Therapy:** For highly emetogenic chemotherapy, Aprepitant is typically used in combination with a **5-HT3 antagonist** (e.g., Ondansetron) and a **Corticosteroid** (e.g., Dexamethasone). * **Fosaprepitant:** This is a water-soluble prodrug of Aprepitant administered **intravenously**, which is rapidly converted to Aprepitant in the body. * **Indication:** Specifically indicated for the **delayed phase** of chemotherapy-induced nausea and vomiting (CINV), where 5-HT3 antagonists are less effective.

Question 252: What is the most effective antiemetic for controlling cisplatin-induced vomiting?

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

Explanation: ### Explanation **Correct Answer: B. Ondansetron** **Mechanism and Rationale:** Cisplatin is a highly emetogenic chemotherapy agent. It triggers vomiting through two primary pathways: the peripheral pathway (release of serotonin from enterochromaffin cells in the GI tract) and the central pathway (stimulation of the Chemoreceptor Trigger Zone - CTZ). **Ondansetron**, a selective **5-HT3 receptor antagonist**, is considered the first-line and most effective class for preventing **acute** cisplatin-induced emesis (occurring within 24 hours). By blocking 5-HT3 receptors both on vagal afferents in the gut and in the CTZ, it effectively halts the emetic reflex. **Analysis of Incorrect Options:** * **A. Prochlorperazine:** A dopamine (D2) antagonist. While useful for mild nausea or motion sickness, it is significantly less potent than 5-HT3 antagonists for chemotherapy-induced emesis. * **C. Metoclopramide:** A D2 antagonist with some 5-HT3 blocking activity at very high doses. However, its efficacy is lower than ondansetron, and it carries a high risk of extrapyramidal side effects (dystonias). * **D. Aprepitant:** This is an **NK1 receptor antagonist**. While it is highly effective for **delayed** emesis (24–72 hours post-chemotherapy), it is typically used as an *adjunct* to 5-HT3 antagonists rather than as a standalone primary treatment for acute episodes. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** 5-HT3 antagonists (Ondansetron/Palonosetron) are the DOC for acute chemotherapy-induced nausea and vomiting (CINV). * **Side Effects:** The most common side effects of Ondansetron are **headache** and **constipation**. A critical ECG finding to remember is **QT interval prolongation**. * **Combination Therapy:** For highly emetogenic drugs like Cisplatin, the gold standard regimen is a "Triple Therapy": **5-HT3 Antagonist + Dexamethasone + NK1 Antagonist (Aprepitant).**

Question 253: What is the antiemetic of choice in chemotherapy-induced vomiting?

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

Explanation: **Ondansetron (Option B)** is the correct answer because it belongs to the class of **5-HT3 receptor antagonists** [2], which are the first-line agents for the prevention and treatment of chemotherapy-induced nausea and vomiting (CINV). Chemotherapeutic drugs trigger the release of serotonin (5-HT) from enterochromaffin cells in the GI tract, which stimulates vagal afferents via 5-HT3 receptors to activate the vomiting center. Ondansetron effectively blocks these receptors both peripherally and centrally in the Chemoreceptor Trigger Zone (CTZ) [1].**Analysis of Incorrect Options:** * **Metoclopramide (Option A):** A D2 receptor antagonist with prokinetic properties [2]. While used for general nausea or gastroparesis, it is less effective than 5-HT3 antagonists for highly emetogenic chemotherapy and carries risks of extrapyramidal side effects [2]. * **Prochlorperazine (Option C):** A dopamine (D2) antagonist (phenothiazine) [2] primarily used for mild-to-moderate nausea or motion sickness. It is not potent enough to serve as the drug of choice for CINV [2]. * **Nabilone (Option D):** A synthetic cannabinoid used as an adjunct or second-line therapy for CINV when conventional treatments fail. It is not the primary drug of choice due to its sedative and psychotropic side effects.**High-Yield NEET-PG Pearls:** * **Mechanism:** 5-HT3 antagonists are most effective for **acute** emesis (first 24 hours). * **Combination Therapy:** For highly emetogenic drugs (e.g., Cisplatin), a "Triple Regimen" is used: **5-HT3 Antagonist + Dexamethasone + NK1 Receptor Antagonist (Aprepitant).** * **Side Effects:** The most common side effects of Ondansetron are **headache**, constipation, and **QT interval prolongation**. * **Drug of Choice for Pregnancy:** Pyridoxine (Vit B6) + Doxylamine is preferred for NVP (Nausea and Vomiting of Pregnancy).

Question 254: Which of the following is not an H2 blocker?

A. Cimetidine
B. Oxyphenonium (Correct Answer)
C. Roxatidine
D. Ranitidine

Explanation: **Explanation:** The question tests the ability to distinguish between different classes of drugs used in acid-peptic disorders. **1. Why Oxyphenonium is the correct answer:** **Oxyphenonium** is a **synthetic quaternary anticholinergic (antimuscarinic)** drug, not an H2 blocker. It works by blocking M3 receptors on gastric parietal cells and smooth muscles. While it reduces gastric secretions and spasms, it is rarely used today for acid suppression due to its side effect profile (dry mouth, blurred vision, urinary retention). **2. Why the other options are incorrect:** * **Cimetidine, Ranitidine, and Roxatidine** are all competitive **H2 receptor antagonists (H2RAs)**. They work by blocking the histamine H2 receptors on the basolateral membrane of parietal cells, thereby reducing both basal and stimulated gastric acid secretion. * **Roxatidine** is a potent H2 blocker with a longer duration of action than Ranitidine. * **Cimetidine** was the first H2 blocker but is now less preferred due to its side effects and drug interactions. **3. High-Yield Clinical Pearls for NEET-PG:** * **Cimetidine Specifics:** It is a potent inhibitor of **Cytochrome P450** (leading to many drug interactions) and has **anti-androgenic effects** (can cause gynecomastia and erectile dysfunction). * **Potency Order:** Famotidine > Ranitidine > Cimetidine. * **Drug of Choice:** While H2 blockers are used for GERD and PUD, **Proton Pump Inhibitors (PPIs)** are currently the DOC for most acid-peptic diseases due to superior efficacy. * **Tolerance:** A major limitation of H2 blockers is **tachyphylaxis** (rapidly developing tolerance), which does not occur with PPIs.

Question 255: Which drug acts on motilin receptors?

A. Erythromycin (Correct Answer)
B. Tetracycline
C. Norfloxacin
D. Chloramphenicol

Explanation: **Explanation:** The correct answer is **Erythromycin**. **Mechanism of Action:** Erythromycin, a macrolide antibiotic, acts as a **non-peptide motilin receptor agonist**. Motilin is a 22-amino acid peptide hormone secreted by the M cells of the upper small intestine. It plays a crucial role in the stimulation of the **Migrating Motor Complex (MMC)**, which triggers gastrointestinal contractions during the fasting state. By binding to and activating motilin receptors on the smooth muscles of the stomach and duodenum, Erythromycin induces strong antral contractions, thereby promoting gastric emptying. **Analysis of Incorrect Options:** * **B, C, and D (Tetracycline, Norfloxacin, Chloramphenicol):** While these are potent antimicrobial agents, they do not possess any structural affinity for motilin receptors. Their primary mechanisms involve inhibiting protein synthesis (Tetracycline, Chloramphenicol) or DNA gyrase (Norfloxacin), and they do not exert prokinetic effects on the GI tract. **Clinical Pearls for NEET-PG:** * **Clinical Use:** Due to its prokinetic properties, Erythromycin is used off-label for **Diabetic Gastroparesis** and to clear the stomach of blood before endoscopy in patients with upper GI bleeds. * **Side Effect:** The most common side effect of Erythromycin is abdominal cramping and diarrhea, which is a direct extension of its motilin-agonist activity. * **Tachyphylaxis:** Long-term use of Erythromycin as a prokinetic is limited by tachyphylaxis (rapidly diminishing response) due to the downregulation of motilin receptors. * **Other Macrolides:** Newer macrolides like Azithromycin also show some prokinetic activity, but Erythromycin remains the most potent in this regard.

Question 256: All are true regarding metoclopramide except?

A. Increases gastric emptying
B. It is a D2-agonist (Correct Answer)
C. Acts on the chemoreceptor trigger zone (CTZ)
D. Long-term use can cause parkinsonism, galactorrhea, and gynecomastia

Explanation: **Explanation:** Metoclopramide is a substituted benzamide used primarily as a **prokinetic** and **antiemetic** agent. **Why Option B is the correct answer (The False Statement):** Metoclopramide is a **D2-receptor antagonist**, not an agonist. By blocking inhibitory dopamine (D2) receptors in the gastrointestinal tract, it enhances the release of Acetylcholine (ACh) from myenteric neurons, leading to increased GI motility. **Analysis of other options:** * **Option A (True):** It is a potent prokinetic. It increases lower esophageal sphincter (LES) tone and enhances gastric emptying and intestinal transit (upper GI tract). * **Option C (True):** It exerts its antiemetic effect by blocking D2 receptors in the **Chemoreceptor Trigger Zone (CTZ)** of the medulla. At higher doses, it also blocks 5-HT3 receptors. * **Option D (True):** Because it crosses the blood-brain barrier and blocks central D2 receptors, long-term use can lead to **Extrapyramidal Side Effects (EPS)** like Parkinsonism and tardive dyskinesia. Additionally, by blocking the inhibitory effect of dopamine on prolactin release, it causes hyperprolactinemia, leading to **galactorrhea, gynecomastia, and amenorrhea.** **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism Summary:** D2 Antagonism (Central/Peripheral), 5-HT4 Agonism (Prokinetic), and 5-HT3 Antagonism (High-dose antiemetic). * **Drug of Choice:** For Gastroparesis (e.g., Diabetic Gastroparesis). * **Contraindication:** It should never be used in cases of **Mechanical GI obstruction** or **Pheochromocytoma** (can cause hypertensive crisis). * **Comparison:** Domperidone is a similar D2 antagonist but does not cross the BBB, thus it lacks EPS side effects.

Question 257: Terlipressin is used for hematemesis from esophageal varices. By which receptor does it primarily act?

A. V1a (Correct Answer)
B. V1b
C. V2
D. V4

Explanation: **Explanation:** **Terlipressin** is a synthetic analogue of vasopressin (antidiuretic hormone) used as a first-line pharmacological treatment for acute variceal bleeding. **1. Why V1a is Correct:** Terlipressin acts primarily as a selective **V1a receptor agonist**. These receptors are located on the **vascular smooth muscle** of the splanchnic circulation. Activation of V1a receptors causes potent **splanchnic vasoconstriction**, which reduces portal blood flow and decreases portal venous pressure. This reduction in pressure helps to control bleeding from esophageal varices. **2. Why the Incorrect Options are Wrong:** * **V1b (or V3):** These receptors are primarily located in the **anterior pituitary gland** and are involved in the release of ACTH. They do not play a role in hemodynamics or portal hypertension. * **V2:** These receptors are located in the **renal collecting ducts** (mediating water reabsorption via aquaporins) and on vascular endothelium (releasing von Willebrand factor and Factor VIII). While vasopressin acts on V2, Terlipressin is designed to be more selective for V1 to avoid excessive water retention (hyponatremia). * **V4:** There is no clinically relevant "V4" receptor in the context of vasopressin pharmacology. **Clinical Pearls for NEET-PG:** * **Drug of Choice:** Terlipressin is often preferred over octreotide in many guidelines because it has been shown to **improve survival** in patients with variceal bleeding. * **Hepatorenal Syndrome (HRS):** Terlipressin is also the drug of choice for Type 1 HRS, where it helps improve renal perfusion by reversing splanchnic vasodilation. * **Administration:** It is a prodrug; it is slowly converted to lysine-vasopressin in the body, giving it a longer duration of action than natural vasopressin. * **Side Effect:** Watch for ischemic complications (e.g., abdominal pain, chest pain) due to its potent vasoconstrictive properties.

Question 258: Which antiemetic is used in vomiting induced by anticancer drugs?

A. Ondansetron (Correct Answer)
B. Cisapride
C. Metoclopramide
D. Triflupromazine

Explanation: **Explanation:** **Ondansetron** is the correct answer because it is a potent, highly selective **5-HT₃ receptor antagonist**. Cytotoxic chemotherapy drugs cause the release of serotonin (5-HT) from enterochromaffin cells in the GI tract, which stimulates vagal afferents via 5-HT₃ receptors to trigger the vomiting center. Ondansetron blocks these receptors both peripherally (vagus nerve) and centrally (Chemoreceptor Trigger Zone - CTZ), making it the first-line agent for **Chemotherapy-Induced Nausea and Vomiting (CINV)**. **Analysis of Incorrect Options:** * **Cisapride:** A prokinetic agent that acts as a 5-HT₄ agonist. It was primarily used for GERD but is now largely banned due to the risk of fatal cardiac arrhythmias (QT prolongation/Torsades de pointes). * **Metoclopramide:** A D₂ receptor antagonist with prokinetic properties. While it has some antiemetic activity, it is less effective than 5-HT₃ antagonists for highly emetogenic chemotherapy and carries risks of extrapyramidal side effects. * **Triflupromazine:** A phenothiazine antipsychotic that acts as a D₂ antagonist in the CTZ. It is used for general nausea but is not the preferred choice for anticancer drug-induced vomiting due to sedation and extrapyramidal symptoms. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Ondansetron is the DOC for CINV and post-operative nausea/vomiting (PONV). * **Side Effects:** The most common side effects of Ondansetron are **headache** and constipation. It can also cause **QT prolongation**. * **Combination Therapy:** For highly emetogenic drugs (e.g., Cisplatin), Ondansetron is often combined with **Dexamethasone** and **Aprepitant** (NK₁ receptor antagonist) for synergistic effects.

Question 259: A 67-year-old woman is being treated for metastatic ovarian cancer with cisplatin and cyclophosphamide. To prevent nausea and vomiting, she is given an agent that selectively antagonizes 5-hydroxytryptamine-3 (5-HT3) receptors. Which of the following drugs is this patient most likely taking?

A. Dimenhydrinate
B. Dronabinol
C. Metoclopramide
D. Ondansetron (Correct Answer)

Explanation: **Explanation:** The patient is receiving highly emetogenic chemotherapy (Cisplatin). The drug of choice for preventing acute chemotherapy-induced nausea and vomiting (CINV) is a **5-HT3 receptor antagonist**, such as **Ondansetron** [1]. **1. Why Ondansetron is correct:** Cisplatin causes the release of serotonin (5-HT) from enterochromaffin cells in the GI tract [2]. This serotonin stimulates 5-HT3 receptors on vagal afferents and in the Area Postrema (Chemoreceptor Trigger Zone - CTZ) [2]. Ondansetron selectively blocks these receptors, effectively inhibiting the emetic signal [1]. **2. Why other options are incorrect:** * **Dimenhydrinate:** An H1-receptor antagonist used primarily for motion sickness, not for highly emetogenic chemotherapy [1]. * **Dronabinol:** A cannabinoid (CB1 agonist) used as a second-line agent for refractory CINV, but it is not a 5-HT3 antagonist. * **Metoclopramide:** Primarily a D2-receptor antagonist [1]. While it has weak 5-HT3 antagonistic activity at very high doses, it is not the "selective" agent of choice and carries a risk of extrapyramidal side effects [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Drug Class Suffix:** All 5-HT3 antagonists end in **"-setron"** (Granisetron, Palonosetron, Dolasetron) [1]. * **Palonosetron:** Has the longest half-life and is effective against both acute and delayed emesis. * **Side Effects:** The most common side effects of Ondansetron are **headache** and **constipation**. * **ECG Warning:** 5-HT3 antagonists (especially Dolasetron and Ondansetron) can cause **QT interval prolongation** [1]. * **Combination Therapy:** For highly emetogenic regimens, 5-HT3 antagonists are often combined with **Dexamethasone** and **Aprepitant** (NK1 receptor antagonist) for synergistic effects [3].

Question 260: An antiemetic drug that also decreases acid secretion due to its action on H1 receptors is?

A. promethazine (Correct Answer)
B. domperidone
C. metoclopramide
D. ondansetron

Explanation: **Explanation:** **Promethazine** is a first-generation H1-receptor antagonist belonging to the phenothiazine class. It is the correct answer because of its unique multi-receptor profile: 1. **Antiemetic Action:** It blocks H1 receptors in the vestibular apparatus and the Chemoreceptor Trigger Zone (CTZ), making it effective for motion sickness and postoperative nausea. 2. **Effect on Acid Secretion:** While H2 receptors are the primary drivers of gastric acid secretion, H1 receptors also play a minor role in the gastric mucosa. By antagonizing H1 receptors, promethazine can marginally decrease acid secretion, a property not shared by the other listed antiemetics. It also possesses significant anticholinergic (muscarinic) activity, which further contributes to reducing gastric secretions. **Analysis of Incorrect Options:** * **B. Domperidone:** A peripheral D2-receptor antagonist. It acts as a prokinetic by increasing lower esophageal sphincter tone and gastric emptying. It has no effect on H1 receptors or acid secretion. * **C. Metoclopramide:** A central and peripheral D2 antagonist with 5-HT4 agonistic properties. Like domperidone, it is a prokinetic and does not influence H1 receptors. * **D. Ondansetron:** A potent 5-HT3 receptor antagonist. It is the drug of choice for chemotherapy-induced nausea and vomiting (CINV) but does not affect histamine receptors or gastric acid. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC) for Motion Sickness:** Hyoscine (Scopolamine) is preferred for prophylaxis; Promethazine is an alternative. * **Side Effects:** Promethazine causes significant sedation and has "atropine-like" side effects (dry mouth, blurred vision) due to its anticholinergic action. * **Contraindication:** Avoid in children <2 years due to the risk of potentially fatal respiratory depression.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free