Drugs for Gastrointestinal Diseases Practice Questions

Q: A patient undergoing chemotherapy with cisplatin experiences severe nausea. Which of the following drugs is most appropriate for managing this side effect?

Ondansetron. **Explanation:** **Ondansetron** is the drug of choice for managing chemotherapy-induced nausea and vomiting (CINV), particularly with highly emetogenic agents like **Cisplatin** [4]. **Mechanism of Action:** 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 Chemoreceptor Trigger Zone (CTZ) [2], [5]. Ondansetron is a potent, selective 5-HT3 receptor antagonist that blocks these signals, effectively controlling the emetic reflex [5]. **Analysis of Incorrect Options:** * **Scopolamine (Hyoscine):** An anticholinergic used primarily for **motion sickness** [4]. It acts on the vestibular system [2] and is ineffective against the peripheral chemical triggers of chemotherapy. * **Naloxone:** An **opioid receptor antagonist** used to reverse opioid overdose. It has no antiemetic properties. * **Cyclizine:** An H1-receptor antihistamine used for motion sickness and postoperative nausea [1], [4]. It is significantly less effective than 5-HT3 antagonists for cisplatin-induced emesis [1]. **Clinical Pearls for NEET-PG:** * **Highly Emetogenic Protocol:** For Cisplatin, a "triple therapy" is often used: **5-HT3 Antagonist + Dexamethasone + NK1 Receptor Antagonist** (e.g., Aprepitant) [3]. * **Side Effects:** The most common side effects of Ondansetron are **headache** and **constipation**. It can also cause **QT interval prolongation** [3]. * **Palonosetron:** A second-generation 5-HT3 antagonist with a longer half-life, often preferred for delayed emesis [5].

Q: What is the drug of choice for gut sterilization in a patient with hepatic encephalopathy?

Neomycin. **Explanation:** **Hepatic Encephalopathy (HE)** is primarily caused by the accumulation of ammonia ($NH_3$), which is produced by the action of urease-positive bacteria in the gut. To manage this, "gut sterilization" (reduction of ammonia-producing flora) is a key therapeutic strategy. **Why Neomycin is the Correct Answer:** Neomycin is an aminoglycoside that is **poorly absorbed** from the gastrointestinal tract when taken orally. It remains in the gut lumen, where it exerts a local bactericidal effect against ammonia-producing organisms. By reducing the bacterial load, it decreases the production and absorption of ammonia into the portal circulation, thereby improving neurological symptoms. **Analysis of Incorrect Options:** * **Netilmicin:** While also an aminoglycoside, it is typically administered parenterally for systemic infections. It is not used for gut sterilization as it lacks the specific clinical history and local profile established for HE. * **Bleomycin:** This is a cytotoxic antibiotic used as a chemotherapy agent (primarily for testicular cancer and lymphomas). It has no role in treating bacterial overgrowth or hepatic encephalopathy. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (Current):** While Neomycin is the traditional answer for gut sterilization, **Rifaximin** (a non-absorbable derivative of Rifampin) is now clinically preferred due to its superior safety profile and lower risk of ototoxicity and nephrotoxicity. * **Mechanism of Lactulose:** Often used alongside antibiotics, Lactulose is a non-absorbable disaccharide that is fermented into lactic acid. This acidifies the gut ($NH_3 \to NH_4^+$), trapping ammonia in its ionized form so it cannot be absorbed (ammonia trapping). * **Side Effects:** Long-term use of Neomycin can lead to malabsorption syndrome and potential systemic toxicity if even small amounts are absorbed in patients with renal failure.

Q: Which of the following drugs increases gastrointestinal motility?

Neostigmine. **Explanation:** The gastrointestinal (GI) tract is primarily regulated by the parasympathetic nervous system via acetylcholine (ACh). Activation of muscarinic receptors (M3) by ACh leads to increased smooth muscle contraction and enhanced GI motility. **Why Neostigmine is Correct:** Neostigmine is an **acetylcholinesterase inhibitor**. By inhibiting the enzyme that breaks down acetylcholine, it increases the concentration of endogenous ACh at the neuromuscular junction and muscarinic sites. This results in increased intestinal peristalsis. Clinically, Neostigmine is used in the management of paralytic ileus and Ogilvie’s syndrome (acute colonic pseudo-obstruction). **Why the Other Options are Incorrect:** * **Glycopyrrolate & Atropine:** These are **antimuscarinic (anticholinergic) agents**. They block M3 receptors in the gut, leading to decreased secretions and reduced GI motility (antispasmodic effect). They are often used to reduce secretions during anesthesia or to treat bradycardia. * **Fentanyl:** This is a potent **opioid analgesic**. Opioids act on $\mu$-receptors in the myenteric plexus to inhibit ACh release, significantly decreasing GI motility and leading to constipation (Opioid-Induced Constipation). **High-Yield Clinical Pearls for NEET-PG:** * **Prokinetic Agents:** Other drugs that increase motility include Metoclopramide and Domperidone (D2 antagonists), and Erythromycin (Motilin receptor agonist). * **Side Effects:** Because Neostigmine increases parasympathetic activity, it can cause bradycardia, salivation, and bronchospasm. Atropine is often co-administered to block these systemic muscarinic side effects when reversing neuromuscular blockade. * **Contraindication:** Neostigmine should never be used if a mechanical intestinal obstruction is suspected, as it may lead to perforation.

Q: Which of the following drugs is used for the treatment of steroid-resistant Crohn's disease?

Infliximab. **Explanation:** **Infliximab** is a chimeric monoclonal antibody that binds to and neutralizes **Tumor Necrosis Factor-alpha (TNF-α)**, a key pro-inflammatory cytokine involved in the pathogenesis of Inflammatory Bowel Disease (IBD). In clinical practice, Infliximab is the drug of choice for patients with **moderate-to-severe Crohn’s disease** who have an inadequate response to conventional therapy (corticosteroids or immunosuppressants) or those with **fistulizing Crohn’s disease**. **Analysis of Options:** * **Leflunomide (Option A):** This is a pyrimidine synthesis inhibitor (DHODH inhibitor) primarily used in the treatment of Rheumatoid Arthritis. It is not a standard treatment for Crohn’s disease. * **Mesalamine (Option B):** A 5-Aminosalicylic acid (5-ASA) derivative. While it is a first-line agent for inducing and maintaining remission in mild-to-moderate **Ulcerative Colitis**, it has limited efficacy in Crohn’s disease and is certainly not effective for steroid-resistant cases. **High-Yield NEET-PG Pearls:** 1. **TNF-α Inhibitors:** Other agents used in Crohn’s include Adalimumab and Certolizumab. 2. **Anti-Integrin Therapy:** **Vedolizumab** is used for patients who fail TNF-α inhibitors; it is gut-selective (binds to α4β7 integrin). 3. **IL-12/23 Inhibitor:** **Ustekinumab** is another biological option for refractory Crohn’s. 4. **Pre-requisite:** Before starting Infliximab, always screen for **Latent Tuberculosis** (PPD/IGRA) and Hepatitis B, as TNF inhibitors can cause reactivation. 5. **Side Effect:** Infliximab can lead to the development of "Antidrug Antibodies" (ADAs), which may reduce its efficacy over time.

Q: Which of the following drugs is known to cause extrapyramidal adverse effects?

Metoclopramide. The correct answer is **Metoclopramide**.1. Why Metoclopramide is correct:Metoclopramide is a potent **D2 receptor antagonist** used as a prokinetic and antiemetic. Its mechanism involves blocking dopamine receptors in the Chemoreceptor Trigger Zone (CTZ). Crucially, metoclopramide is a lipophilic molecule that **crosses the blood-brain barrier (BBB)**. By blocking D2 receptors in the nigrostriatal pathway of the basal ganglia, it disrupts the dopaminergic-cholinergic balance, leading to **Extrapyramidal Side Effects (EPS)** such as acute dystonia, akathisia, and parkinsonism (especially in children and young adults) [1].2. Why the other options are incorrect:* **Domperidone:** While also a D2 receptor antagonist, it **does not cross the BBB** effectively (it acts on the CTZ which lies outside the BBB). Therefore, it is virtually free of EPS. Its primary side effects are related to hyperprolactinemia (galactorrhea, gynecomastia) because the pituitary gland is also outside the BBB.* **Cisapride:** This is a **5-HT4 receptor agonist** that increases ACh release in the myenteric plexus. It does not have significant D2 blocking activity and thus does not cause EPS. (Note: It was largely withdrawn due to QT interval prolongation and *Torsades de Pointes*) [2].High-Yield Clinical Pearls for NEET-PG:* **Drug of Choice:** Metoclopramide is the drug of choice for **Diabetic Gastroparesis**.* **Management of EPS:** If metoclopramide induces acute dystonia, the treatment of choice is an intravenous anticholinergic like **Promethazine** or **Diphenhydramine**.* **Contraindication:** Avoid metoclopramide in patients with **Parkinson’s disease** (exacerbates symptoms) and **Mechanical Bowel Obstruction** (risk of perforation due to prokinetic action).

Q: Omeprazole is used in the treatment of which of the following conditions?

Peptic Ulcer. Omeprazole is a **Proton Pump Inhibitor (PPI)**. It works by irreversibly inhibiting the **H+/K+ ATPase enzyme** (the "proton pump") located in the gastric parietal cells. This is the final common pathway for acid secretion [3]. By significantly reducing gastric acid production, Omeprazole allows the gastric and duodenal mucosa to heal, making it the first-line treatment for **Peptic Ulcer Disease (PUD)**, GERD, and Zollinger-Ellison Syndrome [1, 2]. **2. Why Other Options are Incorrect:** * **Amoebiasis:** This is a protozoal infection caused by *Entamoeba histolytica*. It is treated with luminal amebicides (e.g., Diloxanide furoate) or tissue amebicides (e.g., **Metronidazole**). * **Malaria:** This is caused by *Plasmodium* species and requires antimalarial drugs like **Chloroquine**, Artemisinin derivatives, or Quinine. * **Cholera:** Caused by *Vibrio cholerae*, the mainstay of treatment is aggressive **rehydration (ORS/IV fluids)** and antibiotics like Doxycycline or Azithromycin to reduce stool volume. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** PPIs are **prodrugs** that require an acidic environment (activated in the canaliculi of parietal cells) to form a reactive sulfenamide. * **Administration:** They should be taken **30–60 minutes before meals** (usually breakfast) for maximum efficacy, as the number of proton pumps is highest after a period of fasting. * **Side Effects:** Long-term use is associated with **Hypomagnesemia**, Vitamin B12 deficiency, and an increased risk of *Clostridium difficile* infections and osteoporotic fractures (due to decreased calcium absorption). * **Drug Interaction:** Omeprazole can inhibit CYP2C19, potentially reducing the activation of the antiplatelet drug **Clopidogrel**.

Q: Proton pump inhibitors inhibit which of the following in the parietal cells of the stomach?

H+ K+ ATPase. **Explanation:** **Mechanism of Action (Why A is correct):** Proton Pump Inhibitors (PPIs) like Omeprazole and Pantoprazole are prodrugs that require an acidic environment to be converted into their active form (sulfenamide). Once activated, they form a covalent disulfide bond with the **H+ K+ ATPase enzyme** (the "proton pump") located on the apical membrane of gastric parietal cells. This results in **irreversible inhibition** of the final step of gastric acid secretion, effectively blocking the transport of hydrogen ions into the stomach lumen in exchange for potassium ions. **Analysis of Incorrect Options:** * **B. Na+ Ca+ ATPase:** This transporter is primarily involved in maintaining cellular calcium homeostasis (notably in cardiac myocytes) and is not the target for acid-suppressing drugs. * **C & D. Ligand-gated channels:** Gastric acid secretion is regulated by ligands (Histamine, Gastrin, Acetylcholine), but these act on specific receptors (H2, CCK2, M3) rather than directly gating ion channels. PPIs act downstream of these receptors on the enzymatic pump itself. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** PPIs are the DOC for Peptic Ulcer Disease (PUD), GERD, and Zollinger-Ellison Syndrome. * **Administration:** They should be taken **30–60 minutes before meals** (usually breakfast) because the number of H+ K+ ATPase pumps is highest after a period of fasting. * **Nature of Inhibition:** Though they have a short plasma half-life (~1.5 hours), their duration of action is long (24–48 hours) because the inhibition is **irreversible**; new pumps must be synthesized to resume acid secretion. * **Adverse Effects:** Long-term use is associated with Vitamin B12 deficiency, hypomagnesemia, and increased risk of *C. difficile* infections.

Q: Atropine is added with diphenoxylate to achieve which of the following?

Decrease abuse potential. **Explanation:** **Diphenoxylate** is a synthetic opioid derivative used as an anti-diarrheal agent. It works by activating $\mu$-opioid receptors in the gastrointestinal tract, thereby decreasing intestinal motility. **Why Option C is correct:** Although diphenoxylate is used for its peripheral effects on the gut, it is structurally related to pethidine. At high doses, it can cross the blood-brain barrier and produce opioid-like euphoria and physical dependence. To prevent such misuse, a sub-therapeutic (non-pharmacological) dose of **Atropine** is added. If an individual attempts to take a large dose of the combination to achieve a "high," they will experience the unpleasant symptoms of atropine toxicity (anticholinergic effects) such as dry mouth, blurred vision, palpitations, and urinary retention [1], [2]. This serves as a **deterrent**, effectively decreasing the drug's abuse potential. **Why other options are incorrect:** * **A & D:** Atropine does not synergize with diphenoxylate’s anti-diarrheal efficacy nor does it improve its pharmacokinetic profile (absorption). * **B:** Atropine actually *adds* its own side effects to the profile rather than decreasing those of diphenoxylate [2]. **High-Yield NEET-PG Pearls:** * **Lomotil:** The brand name for the combination of Diphenoxylate + Atropine. * **Loperamide:** Another opioid anti-diarrheal; it is preferred over diphenoxylate because it has poor CNS penetration and a lower abuse potential, so it does not require atropine addition. * **Contraindication:** Avoid these agents in infectious diarrhea (e.g., *Salmonella*, *Shigella*) as they may delay the clearance of organisms and lead to toxic megacolon [3].

Q: Which of the following drugs crosses the blood-brain barrier?

Diphenoxylate. ### Explanation **Correct Answer: D. Diphenoxylate** **Mechanism and Concept:** Diphenoxylate is a synthetic opioid derivative used as an anti-motility agent for diarrhea. Unlike many other peripheral opioids, diphenoxylate is structurally related to pethidine and is lipid-soluble enough to **cross the blood-brain barrier (BBB)**. At high therapeutic doses, it can produce central opioid effects (euphoria and sedation). To prevent drug abuse, it is commercially formulated in combination with a sub-therapeutic dose of **Atropine** (Lomotil), which causes unpleasant anticholinergic side effects if taken in excess. **Analysis of Incorrect Options:** * **A. Loperamide:** Although it is an opioid derivative, it does **not** cross the BBB in significant amounts under normal conditions. It is a substrate for the **P-glycoprotein (P-gp) efflux pump**, which actively pumps the drug out of the brain. Thus, it lacks central effects and has no abuse potential. * **B. Kaolin:** This is a naturally occurring hydrated aluminum silicate. It acts as an **adsorbent** that binds toxins and water in the GI tract. It is not absorbed systemically and therefore cannot cross the BBB. * **C. Methylcellulose:** This is a **bulk-forming laxative** (hydrophilic colloid). It absorbs water to increase stool bulk and promote peristalsis. It is pharmacologically inert and remains within the lumen of the gut. **NEET-PG High-Yield Pearls:** * **Loperamide** is the drug of choice for non-infectious traveler’s diarrhea because it lacks CNS side effects. * **Eluxadoline** is a newer mu-opioid receptor agonist used for Irritable Bowel Syndrome with Diarrhea (IBS-D). * **Racecadotril** is an enkephalinase inhibitor used in pediatric diarrhea; it increases endogenous enkephalins to reduce intestinal secretion without affecting motility.

Question 1

A patient undergoing chemotherapy with cisplatin experiences severe nausea. Which of the following drugs is most appropriate for managing this side effect?

Accepted Answer

Ondansetron

Answer

Scopolamine

Answer

Naloxone

Answer

Cyclizine

Question 2

What is the drug of choice for gut sterilization in a patient with hepatic encephalopathy?

Accepted Answer

Neomycin

Answer

Netilmicin

Answer

Bleomycin

Answer

None of the above

Question 3

Which of the following drugs increases gastrointestinal motility?

Accepted Answer

Neostigmine

Answer

Glycopyrrolate

Answer

Atropine

Answer

Fentanyl

Question 4

Which of the following statements about Omeprazole is true?

Accepted Answer

It may induce carcinoid tumors in rats.

Answer

It may cause leiomyosarcoma.

Answer

It is a nitrosamine.

Answer

It is used more frequently by IV route than orally.

Question 5

Which of the following drugs is used for the treatment of steroid-resistant Crohn's disease?

Accepted Answer

Infliximab

Answer

Leflunomide

Answer

Mesalamine

Answer

None of the above

Question 6

Which of the following drugs is known to cause extrapyramidal adverse effects?

Accepted Answer

Metoclopramide

Answer

Domperidone

Answer

Cisapride

Answer

All of the above

Question 7

Omeprazole is used in the treatment of which of the following conditions?

Accepted Answer

Peptic Ulcer

Answer

Amoebiasis

Answer

Malaria

Answer

Cholera

Question 8

Proton pump inhibitors inhibit which of the following in the parietal cells of the stomach?

Accepted Answer

H+ K+ ATPase

Answer

Na+ Ca+ ATPase

Answer

Ligand gated K+ channel

Answer

Ligand gated Ca+ channel

Question 9

Atropine is added with diphenoxylate to achieve which of the following?

Accepted Answer

Decrease abuse potential

Answer

Increase effect

Answer

Decrease side effects

Answer

Enhance absorption

Question 10

Which of the following drugs crosses the blood-brain barrier?

Accepted Answer

Diphenoxylate

Answer

Loperamide

Answer

Kaolin

Answer

Methylcellulose

Drugs for Gastrointestinal Diseases — MCQs

Drugs for Gastrointestinal Diseases — MCQs

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