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Classification of Drugs Used in Diarrhea

This section provides an overview of the main drug classes used in the management of diarrhea, their mechanisms of action, common adverse effects, and contraindications.


1. Antimotility Agents (Opioid Agonists)

  • Examples: Loperamide, Diphenoxylate
  • Mechanism of Action: Act on opioid receptors in the gastrointestinal (GI) tract to reduce peristalsis and prolong intestinal transit time, aiding in fluid and electrolyte absorption.
  • Adverse Effects: Constipation, abdominal cramping, dizziness, and central nervous system depression (at high doses).
  • Contraindications: Avoid in bacterial infections with bloody diarrhea (e.g., Shigella, Salmonella) as it can exacerbate the condition by slowing transit.

2. Adsorbents

  • Examples: Activated Charcoal, Kaolin-Pectin, Polycarbophil
  • Mechanism of Action: Bind toxins and bacteria in the intestine, reducing fluid secretion and frequency of stools.
  • Adverse Effects: Constipation, bloating, and decreased absorption of some medications.
  • Contraindications: Use cautiously in chronic diarrhea or GI obstruction.

3. Antisecretory Agents

  • Examples: Bismuth Subsalicylate
  • Mechanism of Action: Inhibits prostaglandin synthesis in the intestines, reducing inflammation and fluid secretion.
  • Adverse Effects: Dark stools, black tongue, tinnitus (with prolonged use).
  • Contraindications: Avoid in patients with salicylate allergy or in children with viral infections (risk of Reye’s syndrome).

4. Probiotics

  • Examples: Lactobacillus, Saccharomyces boulardii
  • Mechanism of Action: Restore beneficial gut flora, strengthening the intestinal barrier and suppressing harmful pathogens.
  • Adverse Effects: Generally well-tolerated; may cause mild bloating and gas.
  • Contraindications: Avoid in immunocompromised patients due to infection risk.

5. Oral Rehydration Solution (ORS)

  • Examples: ORS packets with electrolytes (sodium, potassium) and glucose
  • Mechanism of Action: Replaces lost fluids and electrolytes, restoring hydration and electrolyte balance.
  • Adverse Effects: None if used correctly.
  • Contraindications: Not suitable as sole treatment for severe dehydration or shock; IV rehydration may be required in such cases.

6. Parenteral (IV) Fluid Management for Severe Dehydration

  • Fluids Used: Ringer's Lactate (preferred), Normal Saline (0.9% sodium chloride) if Ringer’s Lactate is unavailable.
  • Volume and Rate:
    • Children: Initial bolus of 20 mL/kg over 15–30 minutes, repeat if necessary. Follow with 100 mL/kg over the next 4–6 hours as per response.
    • Adults: Initial 1,000 mL (1 liter) over 30 minutes to 1 hour, then 2,000–3,000 mL over 24 hours based on clinical response.
  • Monitoring: Observe vital signs, urine output, and electrolyte balance to avoid overhydration.
  • Shift to Oral Rehydration: Transition to ORS as soon as the patient can tolerate oral intake.


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