Antidiarrheal Drugs

Antidiarrheal Drugs: Overview - The Run Stoppers

• Diarrhea: Defined by increased stool frequency (>3/day), liquidity, or volume.
• Therapeutic Goals: Control symptoms, prevent dehydration, reduce fluid & electrolyte loss.
• Crucial Management: Oral Rehydration Therapy (ORT) with Oral Rehydration Solution (ORS) is paramount, especially in children.
• Main Drug Classes:
  • Opioid Agonists: Decrease gut motility. E.g., Loperamide, Diphenoxylate (combined with Atropine to deter abuse). 📌 LOpeRAMide = LOw ReAch to brain (peripheral action).
  • Adsorbents: Bind toxins, bacteria, and water. E.g., Kaolin-Pectin, Attapulgite, Bismuth Subsalicylate (also antisecretory, antimicrobial).
  • Antisecretory Agents: Reduce intestinal fluid secretion. E.g., Racecadotril (enkephalinase inhibitor), Octreotide (somatostatin analog for specific diarrheas).
  • Probiotics: Restore normal gut flora. E.g., Lactobacillus spp., Saccharomyces boulardii.

⭐ Loperamide, a µ-opioid agonist, acts peripherally on gut motility with minimal CNS penetration at standard therapeutic doses, making it a preferred agent for symptomatic relief of acute diarrhea without an infectious cause requiring specific antimicrobial therapy.

Antidiarrheal Drugs: Opioids - Gut Slow Mo

• Mechanism: Act on μ (mu) & δ (delta) opioid receptors in GIT.
  • ↓ Intestinal motility, ↑ segmentation, ↑ intestinal transit time.
  • ↑ Water & electrolyte absorption; ↑ anal sphincter tone.
• Loperamide (Imodium):
  • Peripheral action; minimal CNS penetration (P-glycoprotein efflux substrate).
  • DOC: Traveler's diarrhea.
  • Dose: 4 mg stat, then 2 mg after each loose stool (max 16 mg/day).
  • ⚠️ High doses: Cardiac toxicity (QT prolongation, Torsades de Pointes).
  • 📌 "LOPE-RAMIDE LOW-PENETRATION" (low CNS penetration).
• Diphenoxylate (Lomotil):
  • Higher doses → CNS effects; potential for abuse.
  • Combined with Atropine (0.025 mg) to deter abuse.
  • CI: Children < 2 years, obstructive jaundice, acute ulcerative colitis.
• Codeine Phosphate:
  • Central & peripheral action; constipating effect.
  • Analgesic, antitussive. Risk of dependence.
• Eluxadoline (Viberzi):
  • Mixed μ-opioid receptor agonist, δ-opioid receptor antagonist, κ-opioid receptor agonist.
  • Indicated for Irritable Bowel Syndrome with Diarrhea (IBS-D).
  • ⚠️ Risk of pancreatitis (esp. in patients without a gallbladder).

⭐ Loperamide is generally preferred over diphenoxylate due to its significantly lower CNS penetration (actively removed by P-glycoprotein efflux pump) and consequently lower abuse potential.

Antidiarrheal Drugs: Adsorbents & Antisecretory - Toxin Sponges

• Adsorbents (Toxin Sponges)

  • Mechanism: Adsorb toxins, bacteria, water; coat mucosa.
  • Examples:
    • Kaolin-Pectin: Natural clays.
    • Activated Charcoal: Potent; mainly for poisoning.
    • Bismuth Subsalicylate (BSS): Adsorbent, antisecretory, antimicrobial.
      • Black stools (harmless).
      • ⚠️ Reye's syndrome risk (children, viral illness).
  • SE: Constipation, ↓drug absorption.

• Antisecretory Agents

  • Bismuth Subsalicylate (BSS):
    • Salicylate: ↓Prostaglandin synthesis & Cl⁻ secretion.
    • Bismuth: Antimicrobial.
    • Uses: Traveler's diarrhea, dyspepsia.
  • Racecadotril:
    • Enkephalinase inhibitor → ↑enkephalins → ↓intestinal hypersecretion.
    • No motility effect; less constipation.
    • Use: Acute watery diarrhea.

    ⭐ Racecadotril: prodrug to thiorphan; peripheral action, reduces stool output & diarrhea duration.

  • Octreotide:
    • Somatostatin analog.
    • ↓GI hormones, ↓fluid/electrolyte secretion, ↓motility.
    • Uses: Severe secretory diarrheas (carcinoid, VIPoma). Parenteral.

Antidiarrheal Drugs: Probiotics & Management - Flora Fixers

• Probiotics: Live beneficial microbes.
  • E.g.: Lactobacillus sp., Bifidobacterium sp., Saccharomyces boulardii.
  • MOA: Restore flora, ↑barrier, ↓pathogens.
  • Uses: Antibiotic-associated diarrhea (AAD), acute infectious diarrhea, IBS.

⭐ Saccharomyces boulardii is a yeast probiotic, uniquely resistant to antibacterial antibiotics, making it ideal for AAD prevention/treatment.

• General Management Approach:
  • Cornerstone: Oral Rehydration (ORS) / IV fluids.
  • Nutritional support.
  • Antimicrobials: If specific pathogen.
  • Probiotics: Adjunctive therapy.

High‑Yield Points - ⚡ Biggest Takeaways

• Loperamide: Peripherally acting opioid agonist; avoid in bloody diarrhea & children <2 years.
• Diphenoxylate: Opioid agonist, combined with atropine (Lomotil) to deter abuse.
• Racecadotril: Enkephalinase inhibitor, reduces hypersecretion, motility unaffected; safer in children.
• Octreotide: Somatostatin analog for secretory diarrheas (e.g., carcinoid, VIPoma).
• Bismuth subsalicylate: Antisecretory, anti-inflammatory, antimicrobial; causes black stools/tongue.
• Probiotics: Useful for antibiotic-associated and certain infectious diarrheas.
• Antidiarrheals are generally contraindicated in invasive bacterial dysentery (high fever, bloody stools).