Drugs for Gastrointestinal Diseases Practice Questions

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

Agonist at Neurokinin receptor (NK1). **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.

Q: All are true regarding metoclopramide except?

It is a D2-agonist. **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.

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

V1a. **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.

Q: Which newer aminosalicylate is known to cause watery diarrhea due to increased secretion of fluid in the small bowel?

Olsalazine. ### Explanation **Correct Answer: A. Olsalazine** **Mechanism and Rationale:** Olsalazine is a prodrug consisting of two molecules of **5-ASA (Mesalamine)** linked by an azo bond. This bond is cleaved by colonic bacteria to release the active drug in the colon. However, olsalazine has a unique side effect: it stimulates **secretory diarrhea** in approximately 10–15% of patients. This occurs because the unabsorbed olsalazine molecule promotes the secretion of chloride and water in the small bowel (via a cyclic AMP-mediated mechanism) before it reaches the colon for cleavage. This "watery diarrhea" is a classic, high-yield side effect that often limits its clinical use compared to other aminosalicylates. **Analysis of Incorrect Options:** * **B. 5-ASA & C. Mesalamine:** These are the same compound. Mesalamine is the active moiety used in Ulcerative Colitis. While it can cause GI upset or headache, it is not specifically associated with the paradoxical induction of secretory diarrhea; in fact, it is used to *treat* the inflammation that causes diarrhea. * **D. Balsalazide:** This is another prodrug where 5-ASA is linked to an inert carrier (4-aminobenzoyl-β-alanine). Like olsalazine, it is activated in the colon, but it does not possess the same secretagogue effect on the small intestinal mucosa and is generally better tolerated. **NEET-PG High-Yield Pearls:** * **Sulfasalazine** (5-ASA + Sulfapyridine) is the older prototype. Its side effects (malaise, hemolysis, sperm count reduction) are mostly due to the **Sulfapyridine** moiety. * **Olsalazine and Balsalazide** were developed to deliver 5-ASA to the colon while avoiding the toxicity of sulfapyridine. * **Key Distinction:** If a question mentions "diarrhea as a side effect" in a patient being treated for "bloody diarrhea (UC)," think **Olsalazine**.

Q: Ondansetron acts by:

Action on CTZ. **Explanation:** **Ondansetron** is a potent antiemetic primarily used to control chemotherapy-induced nausea and vomiting (CINV). **Why Option A is correct:** The primary site of action for Ondansetron is the **Chemoreceptor Trigger Zone (CTZ)** located in the *Area Postrema* of the medulla. The CTZ is rich in 5-HT3 receptors. By blocking these receptors, Ondansetron prevents the activation of the vomiting center. While it also works on peripheral vagal nerve terminals in the gastrointestinal tract, its central action on the CTZ is the definitive mechanism for its potent antiemetic effect. **Why other options are incorrect:** * **Option B:** While Ondansetron is indeed a **5-HT3 antagonist**, in the context of this specific question format (often seen in older NEET-PG/AIIMS patterns), the "Action on CTZ" is considered the anatomical site of action, whereas 5-HT3 antagonism is the molecular mechanism. If both are present, the site (CTZ) is often prioritized as the primary answer. * **Option C:** D1 and D2 receptor antagonism is the mechanism of drugs like **Metoclopramide** and **Domperidone**, not Ondansetron. * **Option D:** Increasing GIT motility (Prokinetic action) is characteristic of drugs like Metoclopramide and Cisapride. Ondansetron actually tends to **decrease** colonic motility, often leading to constipation. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For CINV and post-operative nausea and vomiting (PONV). * **Side Effects:** The most common side effect is **headache**. It is also notorious for causing **QT interval prolongation** and **constipation**. * **Metabolism:** It is metabolized by the liver; dose adjustment is required in severe hepatic impairment. * **Note:** It is *not* effective in motion sickness (where H1 and M1 blockers are used).

Q: All of the following drugs are used for eradication of Helicobacter pylori except?

Sucralfate. **Explanation:** The goal of *Helicobacter pylori* eradication is to eliminate the bacteria using a combination of acid suppressants (PPIs) and antimicrobial agents. **Why Sucralfate is the correct answer:** **Sucralfate** is a complex of sulfated sucrose and aluminum hydroxide. It acts as a **physical mucosal protective agent** by polymerizing in an acidic environment (pH < 4) to form a sticky paste that adheres to the ulcer base. While it promotes healing and provides a barrier against acid and pepsin, it possesses **no intrinsic antibacterial activity** against *H. pylori*. Therefore, it is not included in standard eradication regimens (Triple or Quadruple therapy). **Analysis of incorrect options:** * **Bismuth subcitrate (Option A):** This is a key component of **Bismuth-based Quadruple Therapy**. It has direct toxic effects on *H. pylori*, inhibits its enzymes (urease, catalase), and prevents bacterial adhesion to the gastric epithelium. * **Metronidazole (Option C):** An imidazole antibiotic frequently used in both Triple and Quadruple therapies, especially in patients allergic to penicillin or in areas with low nitroimidazole resistance. * **Moxifloxacin (Option D):** A second-line fluoroquinolone used in **"Rescue Therapy"** for patients who have failed initial standard treatments. **NEET-PG High-Yield Pearls:** 1. **Standard Triple Therapy (7-14 days):** PPI + Amoxicillin + Clarithromycin (Mnemonic: **PAC**). 2. **Bismuth Quadruple Therapy:** PPI + Bismuth + Metronidazole + Tetracycline (Mnemonic: **PBM-T**). This is now preferred in areas with high clarithromycin resistance. 3. **Sequential Therapy:** 5 days of PPI + Amoxicillin, followed by 5 days of PPI + Clarithromycin + Tinidazole. 4. **Sucralfate Note:** It requires an acidic medium to work; therefore, it should **not** be administered simultaneously with antacids or PPIs (give it 1 hour before meals).

Q: Which of the following statements about Racecadotril is false?

It is a drug used in constipation.. **Explanation:** **Racecadotril** is an **antidiarrheal** agent, specifically an **enkephalinase inhibitor**. Its primary mechanism involves preventing the breakdown of endogenous enkephalins (opioid peptides) in the gastrointestinal tract. 1. **Why Option B is the correct (False) statement:** Racecadotril is used to treat **acute secretory diarrhea**, not constipation. By protecting enkephalins, it activates delta-opioid receptors, which decreases the levels of cAMP in the intestinal mucosa. This leads to a potent **antisecretory effect**, reducing the hypersecretion of water and electrolytes into the gut lumen. 2. **Analysis of other options:** * **Option A (True):** It acts peripherally on the enkephalinase enzyme located in the intestinal epithelium. It does not cross the blood-brain barrier, thus avoiding central opioid side effects. * **Option C (True):** Racecadotril is a prodrug. After oral administration, it is rapidly absorbed and **metabolized by the liver** into its active metabolite, thiorphan. * **Option D (True):** Its hallmark is its **antisecretory action**. Unlike loperamide, it does not significantly affect intestinal motility (transit time), which reduces the risk of secondary constipation or abdominal bloating. **High-Yield NEET-PG Pearls:** * **Indication:** Preferred in pediatric diarrhea because it does not cause respiratory depression or paralytic ileus (unlike loperamide). * **Mechanism:** Increases endogenous enkephalins $\rightarrow$ $\downarrow$ cAMP $\rightarrow$ $\downarrow$ water/electrolyte secretion. * **Key Advantage:** It treats diarrhea without causing "rebound constipation." * **Contraindication:** Avoid in diarrhea with blood or pus (dysentery) where antibiotics are primarily required.

Question 1

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

Accepted Answer

Agonist at Neurokinin receptor (NK1)

Answer

Crosses the blood brain barrier

Answer

Metabolized by Cytochrome P450 3A4 pathway

Answer

Ameliorates nausea and vomiting of chemotherapy

Question 2

Which one of the following statements about the management of patients with gastrointestinal ulcers is accurate?

Accepted Answer

Sucralfate polymerizes in the gut, forming a protective coat over ulcer beds.

Answer

Histamine-2 receptor blockers are as effective as proton pump inhibitors for treating GI ulcers.

Answer

Antimicrobial regimens that eradicate Helicobacter pylori are more than 98% effective in treating GI ulcers.

Answer

Omeprazole is effective because it activates prostaglandin E1 receptors.

Question 3

All are true regarding metoclopramide except?

Accepted Answer

It is a D2-agonist

Answer

Increases gastric emptying

Answer

Acts on the chemoreceptor trigger zone (CTZ)

Answer

Long-term use can cause parkinsonism, galactorrhea, and gynecomastia

Question 4

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

Accepted Answer

V1a

Answer

V1b

Answer

V2

Answer

V4

Question 5

Which newer aminosalicylate is known to cause watery diarrhea due to increased secretion of fluid in the small bowel?

Accepted Answer

Olsalazine

Answer

5-ASA

Answer

Mesalamine

Answer

Balsalazide

Question 6

Ondansetron acts by:

Accepted Answer

Action on CTZ

Answer

5-HT3 antagonism

Answer

D1 and D2 receptor antagonism

Answer

Increasing GIT motility

Question 7

All of the following drugs are used for eradication of Helicobacter pylori except?

Accepted Answer

Sucralfate

Answer

Bismuth subcitrate

Answer

Metronidazole

Answer

Moxifloxacin

Question 8

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

Accepted Answer

Proton pump inhibitors

Answer

Antihistamines

Answer

Dopamine agonists

Answer

Antacids

Question 9

Which of the following statements about Racecadotril is false?

Accepted Answer

It is a drug used in constipation.

Answer

It is a peripheral acting enkephalinase inhibitor.

Answer

It is metabolized by the liver.

Answer

It has antisecretory action on the GIT.

Question 10

Which of the following statements is not true about domperidone?

Accepted Answer

Its antiemetic efficacy is higher than metoclopramide.

Answer

It rarely causes extrapyramidal side effects.

Answer

It is a D2 receptor antagonist.

Answer

It causes loose stool.

Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?