Diarrhea and constipation: pharmacological approaches MCQs With Answer

Diarrhea and constipation: pharmacological approaches MCQs With Answer

Introduction: This set of MCQs is designed for M.Pharm students studying Pharmacotherapeutics I (MPP 102T) to deepen understanding of pharmacologic management of diarrheal and constipative disorders. Questions cover mechanisms of action, drug classes, clinical indications, adverse effects, pharmacokinetic interactions, and newer agents such as intestinal secretagogues and peripherally acting opioid antagonists. Emphasis is placed on pathophysiology-driven therapy (secretory vs osmotic diarrhea, opioid-induced constipation, IBS variants) and evidence-based choices (e.g., oral rehydration, antimicrobials for C. difficile, laxative selection and contraindications). These items aim to test both factual recall and application of therapeutic principles in clinical scenarios.

Q1. Which of the following best describes the primary mechanism by which loperamide reduces diarrhoea?

• Inhibition of enteric bacterial toxin binding to epithelial cells
• Peripheral agonism at μ-opioid receptors reducing intestinal motility and secretion
• Blockade of chloride channels on enterocytes to decrease secretion
• Stimulation of 5-HT4 receptors to increase segmental contractions

Correct Answer: Peripheral agonism at μ-opioid receptors reducing intestinal motility and secretion

Q2. Which antisecretory agent acts by inhibiting enkephalinase and thereby reduces intestinal secretion in acute diarrhoea?

• Bismuth subsalicylate
• Racecadotril
• Octreotide
• Attapulgite

Correct Answer: Racecadotril

Q3. Which oral rehydration therapy (ORT) principle explains why glucose is included with sodium in ORS solutions?

• Glucose increases osmotic load to promote water retention in the lumen
• Glucose enhances sodium and water absorption via sodium-glucose cotransport (SGLT1)
• Glucose acidifies intestinal contents to inactivate bacterial toxins
• Glucose stimulates enteric nervous system to decrease motility

Correct Answer: Glucose enhances sodium and water absorption via sodium-glucose cotransport (SGLT1)

Q4. Which of the following is the most appropriate first-line antibiotic for initial severe Clostridioides difficile infection according to current guidelines?

• Oral metronidazole
• Intravenous ceftriaxone
• Oral vancomycin
• Oral erythromycin

Correct Answer: Oral vancomycin

Q5. A patient with opioid-induced constipation refractory to laxatives would most likely benefit from which class of drug?

• Peripherally acting μ-opioid receptor antagonists (PAMORAs) such as methylnaltrexone
• Central opioid antagonists like naloxone given systemically
• 5-HT3 antagonists such as ondansetron
• Bulk-forming agents such as psyllium only

Correct Answer: Peripherally acting μ-opioid receptor antagonists (PAMORAs) such as methylnaltrexone

Q6. Which laxative class works primarily by drawing water into the intestinal lumen and increasing stool volume without directly stimulating enteric nerves?

• Stimulant laxatives (e.g., bisacodyl)
• Bulk-forming laxatives (e.g., psyllium)
• Osmotic laxatives (e.g., polyethylene glycol, lactulose)
• Surfactant/stool softeners (e.g., docusate)

Correct Answer: Osmotic laxatives (e.g., polyethylene glycol, lactulose)

Q7. Which adverse effect is most characteristically associated with use of bismuth subsalicylate in diarrhoea?

• Marked bradycardia
• Black discoloration of tongue and stool
• Acute pancreatitis
• Severe hypokalemia

Correct Answer: Black discoloration of tongue and stool

Q8. Lubiprostone relieves chronic constipation primarily by which mechanism?

• Agonism at the 5-HT4 receptor to enhance peristalsis
• Activation of type-2 chloride channels (ClC-2) on apical enterocytes increasing chloride-rich fluid secretion
• Inhibition of epithelial sodium channels to reduce fluid absorption
• Central stimulation of parasympathetic outflow to gut

Correct Answer: Activation of type-2 chloride channels (ClC-2) on apical enterocytes increasing chloride-rich fluid secretion

Q9. Which agent is a guanylate cyclase-C agonist that increases intracellular cGMP to enhance intestinal secretion and transit, used for chronic idiopathic constipation and IBS-C?

• Linaclotide
• Alosetron
• Diphenoxylate-atropine
• Naloxegol

Correct Answer: Linaclotide

Q10. Which statement about loperamide pharmacokinetics and safety is correct?

• Loperamide freely crosses the blood–brain barrier and causes central opioid effects at therapeutic doses
• Loperamide is a P-glycoprotein substrate, limiting CNS penetration under normal conditions
• Loperamide is a potent CYP3A4 inhibitor leading to many drug interactions
• Loperamide is the preferred systemic antibiotic for traveler’s diarrhoea

Correct Answer: Loperamide is a P-glycoprotein substrate, limiting CNS penetration under normal conditions

Q11. Which of the following is the most appropriate mechanism of action for octreotide when used to treat secretory diarrhoea?

• Somatostatin analogue that inhibits hormone-mediated intestinal secretion (e.g., vasoactive intestinal peptide)
• Nonabsorbable binding resin that adsorbs toxins
• Selective 5-HT3 receptor agonist to reduce nausea
• Cholinergic agonist increasing smooth muscle contraction

Correct Answer: Somatostatin analogue that inhibits hormone-mediated intestinal secretion (e.g., vasoactive intestinal peptide)

Q12. Which of the following is the correct clinical use and important contraindication for stimulant laxatives (e.g., senna, bisacodyl)?

• Useful for long-term daily relief of chronic constipation without risk; contraindicated in pregnancy
• Useful for opioid-induced constipation as first-line; contraindicated in hypertension
• Effective for short-term relief and bowel evacuation; contraindicated in suspected intestinal obstruction or acute abdominal pain
• Primarily used to treat secretory diarrhoea; contraindicated with antibiotics

Correct Answer: Effective for short-term relief and bowel evacuation; contraindicated in suspected intestinal obstruction or acute abdominal pain

Q13. Which drug is a selective 5-HT3 receptor antagonist approved for severe IBS-D in women and is associated with ischemic colitis risk, limiting its use?

• Prucalopride
• Alosetron
• Lubiprostone
• Rifaximin

Correct Answer: Alosetron

Q14. Which antibiotic is FDA-approved for treatment of hepatic encephalopathy by reducing intestinal ammonia-producing bacteria and is often used in diarrheal syndromes with hepatic involvement?

• Rifaximin
• Tetracycline
• Gentamicin
• Azithromycin

Correct Answer: Rifaximin

Q15. A mechanism-based cause of secretory diarrhoea is activation of which intracellular second messenger increasing chloride and water secretion across enterocytes?

• Decreased cAMP levels causing CFTR activation
• Increased cAMP or cGMP leading to CFTR-mediated chloride secretion
• Increased intracellular calcium causing sodium absorption
• Inhibition of guanylate cyclase-C reducing secretion

Correct Answer: Increased cAMP or cGMP leading to CFTR-mediated chloride secretion

Q16. Which laxative is preferred for bowel preparation before colonoscopy and for chronic constipation due to its minimal systemic absorption and osmotic action?

• Lactulose
• Polyethylene glycol (PEG) solutions
• Mineral oil
• Bisacodyl suppositories

Correct Answer: Polyethylene glycol (PEG) solutions

Q17. Which of these agents is an opioid derivative combined with atropine to discourage abuse and is used short-term for diarrhoea?

• Diphenoxylate-atropine
• Loperamide
• Methylnaltrexone
• Naloxone

Correct Answer: Diphenoxylate-atropine

Q18. Which statement is correct regarding lactulose use in hepatic encephalopathy treatment?

• Lactulose acts only as a bulk-forming fiber and has no effect on ammonia production
• Lactulose acidifies colonic contents and promotes conversion of ammonia (NH3) to ammonium (NH4+), reducing absorption
• Lactulose is an antimicrobial that eradicates urease-producing bacteria systemically
• Lactulose is contraindicated because it increases serum ammonia levels

Correct Answer: Lactulose acidifies colonic contents and promotes conversion of ammonia (NH3) to ammonium (NH4+), reducing absorption

Q19. Which of the following antidiarrheal agents is contraindicated in C. difficile infection due to risk of toxic megacolon by reducing colonic transit?

• Loperamide
• Bismuth subsalicylate
• Racecadotril
• Rifaximin

Correct Answer: Loperamide

Q20. Prucalopride, used for chronic constipation, selectively targets which receptor, and why is its selectivity clinically important?

• 5-HT1A receptor; selectivity reduces opioid-related constipation
• 5-HT3 receptor; selectivity reduces nausea but increases motility
• 5-HT4 receptor; high selectivity minimizes cardiac 5-HT4/5-HT2B mediated adverse effects seen with older drugs
• Muscarinic M3 receptor; selectivity enhances fluid secretion in colon

Correct Answer: 5-HT4 receptor; high selectivity minimizes cardiac 5-HT4/5-HT2B mediated adverse effects seen with older drugs

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