• Diarrhoea is a common symptom, not a disease, caused by infections, inflammation, toxins, or digestive disorders. Managing diarrhoea requires a strategic approach involving hydration and specific drug therapies.
• In this blog by Pharmacy Freak, we explore the classification of antidiarrheal drugs, their mechanisms, and clinical applications. We’ve also included standard references from Sparsh Gupta, KDT, and Goodman & Gilman’s, making it ideal for exam preparation and real-world understanding.

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🔍 What Are Antidiarrheal Drugs?

Antidiarrheal drugs reduce the frequency and urgency of stools. They work by:

• Killing infective organisms
• Slowing intestinal motility
• Enhancing fluid absorption
• Replenishing healthy gut bacteria
• Reducing secretions

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📊 Classification of Antidiarrheal Drugs

The drugs are divided into five main categories:

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🧪 1. Antimicrobial Drugs

These are used when the diarrhea is infectious in origin — particularly bacterial or protozoal.

• Fluoroquinolones: Norfloxacin, Ciprofloxacin
• Rifaximin – Poorly absorbed; acts within the gut
• Cotrimoxazole – Used in travel-related diarrhea
• Ampicillin – Occasionally used in children
• Tetracycline, Erythromycin – Useful for Vibrio cholerae
• Metronidazole – DOC for amoebic and Clostridium difficile-associated diarrhea (Sparsh Gupta)

✅ Note: Antimicrobials are not used in all diarrhoea cases. They are avoided in most viral infections and mild food poisoning cases unless warranted.

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🦠 2. Probiotics

Probiotics restore gut flora that may be disrupted by infection or antibiotic use. They help maintain mucosal integrity and reduce pathogen adhesion.

Commonly used strains:

• Lactobacillus spp.
• Bifidobacterium bifidum
• Streptococcus faecalis
• Bacillus clausii
• Enterococcus spp.
• Saccharomyces boulardii – Effective in antibiotic-associated diarrhoea and pseudomembranous colitis (KDT)

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💊 3. Nonspecific Antidiarrhoeal Drugs

These provide symptomatic relief and are used in functional or chronic diarrhoea when no clear infection is identified.

A. Absorbents/Adsorbents

• Kaolin
• Pectin
• Ispaghula (Psyllium)
• Methylcellulose

These bind toxins and excess water in the intestine.

B. Antisecretory Agents

• Racecadotril – Reduces intestinal secretion by acting on enkephalinase (DOC in pediatric acute diarrhoea – Sparsh Gupta)
• Bismuth Subsalicylate – Anti-inflammatory and mild antimicrobial
• Anticholinergics – Reduce motility and secretion (e.g., atropine, dicyclomine)
• Octreotide – Used in VIPoma and chemotherapy-induced diarrhoea (Goodman & Gilman)

C. Antimotility Agents

• Loperamide – Acts on μ-opioid receptors; DOC for traveller’s diarrhoea (unless invasive)
• Diphenoxylate + Atropine
• Codeine – Occasionally used; can cause dependence

🔺 Caution: Avoid antimotility agents in bloody diarrhoea, high fever, or suspected C. difficile infection.

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🔥 4. Drugs for Inflammatory Bowel Disease (IBD)

Used in chronic diarrhoea associated with Ulcerative Colitis or Crohn’s disease.

A. 5-ASA Compounds

• Sulfasalazine – DOC for ulcerative colitis
• Mesalazine (Mesalamine) – Better tolerated
• Balsalazide, Olsalazine – Colon-targeted prodrugs (KDT)

B. Glucocorticoids

• Prednisolone – Used during acute flare-ups
• Hydrocortisone enemas – Local application for distal disease

C. Immunosuppressants

• Azathioprine
• Methotrexate
• Cyclosporine
• Infliximab – A TNF-α inhibitor used for moderate-to-severe IBD resistant to steroids (G&G)

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📈 Current Guidelines & Clinical Pearls

Based on the latest editions:

• Racecadotril is safer in children than loperamide and preferred in acute viral diarrhoea (Sparsh Gupta).
• Rifaximin is the DOC for noninvasive traveler’s diarrhoea (e.g., E. coli).
• In C. difficile colitis, Metronidazole is first-line for mild cases, while Vancomycin is reserved for severe cases (Goodman & Gilman).
• In IBD, 5-ASA derivatives are started first, followed by steroids and immunomodulators if no response.

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📚 References

1. Tripathi KD. Essentials of Medical Pharmacology. 7th ed. Jaypee Brothers Medical Publishers,Chapter-48 Drugs for Constipation and Diarrhea
2. Gupta S, Garg A. Review of Pharmacology. 15th ed. Jaypee Brothers; 2023. p. 246–249.
3. Brunton LL, Chabner BA, Knollmann BC, editors. Goodman and Gilman’s: The Pharmacological Basis of Therapeutics. 12th ed. McGraw-Hill; 2011. p. 1103–1108.

Related Links

• Classification of Cephalosporins
• Classification of Antibacterial Drugs