Understanding drugs for diarrhoea is essential for B.Pharm students. This concise introduction reviews major antidiarrheal drug classes and their mechanisms — antimotility agents (opioid agonists like loperamide and diphenoxylate), antisecretory drugs (racecadotril, bismuth subsalicylate), adsorbents (kaolin-pectin, activated charcoal), antimicrobials for infectious diarrhoea (azithromycin, ciprofloxacin, nitazoxanide), and adjuncts such as oral rehydration salts and zinc. Emphasis is placed on receptor targets, pharmacokinetics, adverse effects (constipation, ileus, toxic megacolon), contraindications, and drug interactions relevant to clinical use and exam preparation. This targeted summary links mechanism to examples to aid rapid learning. Questions cover clinical application, pediatric and geriatric considerations, and pharmacovigilance. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which mechanism best describes how loperamide reduces diarrhoea?
- Inhibition of intestinal chloride channels
- Peripheral μ-opioid receptor agonism reducing gut motility
- Inactivation of bacterial toxins
- Binding bile acids in the gut lumen
Correct Answer: Peripheral μ-opioid receptor agonism reducing gut motility
Q2. Racecadotril exerts its antisecretory effect primarily by which mechanism?
- Direct inhibition of CFTR chloride channel
- Enkephalinase inhibition increasing endogenous enkephalins
- Activation of alpha-2 adrenergic receptors
- Adsorption of enterotoxins
Correct Answer: Enkephalinase inhibition increasing endogenous enkephalins
Q3. Bismuth subsalicylate helps in diarrhoea by which combined actions?
- Antimicrobial, anti-secretory, and mucosal protective effects
- Pure opioid-like antimotility action
- Systemic absorption to neutralize toxins
- Enzyme replacement in lactose intolerance
Correct Answer: Antimicrobial, anti-secretory, and mucosal protective effects
Q4. Which antidiarrheal is contraindicated in acute dysentery with high fever and bloody stools?
- Loperamide
- Bismuth subsalicylate
- Activated charcoal
- Racecadotril
Correct Answer: Loperamide
Q5. Diphenoxylate is often combined with atropine to:
- Enhance opioid receptor binding in the gut
- Prevent central opioid effects and reduce abuse potential
- Increase intestinal secretion
- Promote faster systemic absorption
Correct Answer: Prevent central opioid effects and reduce abuse potential
Q6. Which drug is most appropriate as first-line antisecretory therapy in acute secretory diarrhoea of viral origin?
- Octreotide
- Racecadotril
- Ciprofloxacin
- Cholestyramine
Correct Answer: Racecadotril
Q7. Activated charcoal in diarrhoea acts primarily by:
- Absorbing toxins and pathogens in the gut lumen
- Stimulating intestinal motility
- Neutralizing gastric acid systemically
- Inhibiting mucosal secretions via opioid receptors
Correct Answer: Absorbing toxins and pathogens in the gut lumen
Q8. Which agent is specifically useful for bile acid diarrhoea by sequestering bile acids?
- Cholestyramine
- Loperamide
- Kaolin-pectin
- Racecadotril
Correct Answer: Cholestyramine
Q9. A pharmacokinetic reason loperamide has minimal CNS effects at therapeutic doses is:
- High first-pass metabolism in liver producing inactive metabolites
- Poor absorption from the gut
- P-glycoprotein efflux at the blood–brain barrier limiting CNS penetration
- Strong protein binding preventing CNS entry
Correct Answer: P-glycoprotein efflux at the blood–brain barrier limiting CNS penetration
Q10. Which antibiotic is most commonly recommended for severe traveller’s diarrhoea and campylobacter infections?
- Azithromycin
- Metronidazole
- Penicillin V
- Amoxicillin-clavulanate
Correct Answer: Azithromycin
Q11. Which of the following is a somatostatin analogue used for hormone-related secretory diarrhoea (e.g., VIPoma)?
- Octreotide
- Racecadotril
- Loperamide
- Bismuth subsalicylate
Correct Answer: Octreotide
Q12. Zinc supplementation in acute childhood diarrhoea acts by:
- Replacing fluid losses directly
- Enhancing mucosal repair and immune response
- Blocking opioid receptors
- Acting as an adsorbent to bind toxins
Correct Answer: Enhancing mucosal repair and immune response
Q13. Which antidiarrheal would be inappropriate in a patient with suspected Clostridioides difficile infection?
- Loperamide
- Vancomycin (oral)
- Fidaxomicin
- Metronidazole
Correct Answer: Loperamide
Q14. Which drug’s adverse effects include blackened stool and a temporary dark tongue?
- Bismuth subsalicylate
- Loperamide
- Cholestyramine
- Racecadotril
Correct Answer: Bismuth subsalicylate
Q15. Nitazoxanide is primarily effective against which type of diarrhoeal pathogens?
- Protozoa and certain viral pathogens (e.g., Giardia, Cryptosporidium)
- Gram-positive aerobic bacteria only
- Helminths exclusively
- All enteric viruses uniformly
Correct Answer: Protozoa and certain viral pathogens (e.g., Giardia, Cryptosporidium)
Q16. Which antidiarrheal class acts by coating the gut mucosa and adsorbing toxins and bacteria?
- Adsorbents (e.g., kaolin-pectin, activated charcoal)
- Antisecretory enzymes
- Somatostatin analogues
- Systemic antibiotics
Correct Answer: Adsorbents (e.g., kaolin-pectin, activated charcoal)
Q17. A known drug interaction risk: coadministration of loperamide with a potent P-gp inhibitor may result in:
- Reduced antidiarrheal effect due to decreased absorption
- Increased CNS opioid effects and risk of respiratory depression
- Complete inactivation of loperamide in the gut lumen
- Enhanced biliary excretion of loperamide
Correct Answer: Increased CNS opioid effects and risk of respiratory depression
Q18. Which antidiarrheal is useful in lactose intolerance due to enzyme replacement?
- Lactase enzyme preparations
- Loperamide
- Bismuth subsalicylate
- Cholestyramine
Correct Answer: Lactase enzyme preparations
Q19. In secretory diarrhoea caused by cholera toxin, which mechanism is central to fluid loss?
- Activation of adenylate cyclase increasing cAMP and chloride secretion
- Direct mucosal ulceration causing blood loss
- Enzyme deficiency leading to undigested sugars
- Excess bile acid sequestration
Correct Answer: Activation of adenylate cyclase increasing cAMP and chloride secretion
Q20. Which antidiarrheal is considered safe for short-term use in adults with non-bloody acute diarrhoea and is available OTC in many countries?
- Loperamide
- Diphenoxylate-atropine prescription only
- Octreotide injection
- Cholestyramine prescription only
Correct Answer: Loperamide
Q21. Which agent has a mechanism that increases enterocyte water absorption indirectly by inhibiting secretory mediators?
- Racecadotril
- Cholestyramine
- Activated charcoal
- Probiotics
Correct Answer: Racecadotril
Q22. Probiotics help in acute infectious diarrhoea primarily by:
- Directly neutralizing bacterial endotoxins systemically
- Restoring normal gut flora and competitive inhibition of pathogens
- Binding bile acids to reduce secretion
- Acting as opioid receptor agonists
Correct Answer: Restoring normal gut flora and competitive inhibition of pathogens
Q23. Which antidiarrheal is associated with the risk of toxic megacolon in inflammatory bowel disease?
- Opioid antimotility agents such as loperamide or diphenoxylate
- Cholestyramine
- Oral rehydration salts
- Lactase supplements
Correct Answer: Opioid antimotility agents such as loperamide or diphenoxylate
Q24. Which antimicrobial is preferred for suspected Shigella infection in children in many regions?
- Azithromycin
- Ciprofloxacin universally in all children
- Amoxicillin exclusively
- Rifaximin only
Correct Answer: Azithromycin
Q25. Which statement about bismuth subsalicylate is correct?
- It acts systemically as an anticoagulant
- It contains a salicylate so caution is needed in children
- It is a potent opioid agonist
- It primarily replaces pancreatic enzymes
Correct Answer: It contains a salicylate so caution is needed in children
Q26. Octreotide’s antisecretory effect is mediated by:
- Somatostatin receptor agonism reducing gastrointestinal hormone release
- Direct binding to bacterial toxins
- Activation of opioid receptors in the gut
- Sequestration of bile salts
Correct Answer: Somatostatin receptor agonism reducing gastrointestinal hormone release
Q27. Which drug class would be most effective for diarrhoea due to unabsorbed sugars in lactase deficiency?
- Enzyme replacement (lactase)
- Antibiotics
- Opioid antimotility agents
- Bile acid sequestrants
Correct Answer: Enzyme replacement (lactase)
Q28. The WHO-recommended primary treatment for dehydration caused by diarrhoea is:
- Oral rehydration salts (ORS) with zinc supplementation when indicated
- Immediate use of antidiarrheal opioids
- High-dose systemic antibiotics for all cases
- Fasting and absolute bowel rest
Correct Answer: Oral rehydration salts (ORS) with zinc supplementation when indicated
Q29. Which of the following is a major pharmacovigilance concern with chronic high-dose use of loperamide?
- Cardiac arrhythmias due to QT prolongation at very high doses
- Renal toxicity leading to haemodialysis
- Immediate anaphylaxis in all patients
- Permanent blindness
Correct Answer: Cardiac arrhythmias due to QT prolongation at very high doses
Q30. For community-acquired infectious diarrhoea with severe systemic features, pharmacologic approach should include:
- Appropriate empirical antimicrobials guided by likely pathogen and severity
- Only antidiarrheal OTC medications without antibiotics
- Immediate use of cholestyramine in all cases
- Long-term opioid therapy
Correct Answer: Appropriate empirical antimicrobials guided by likely pathogen and severity
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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