Diarrhea is defined as an increase in the frequency and fluidity of stools. A healthy adult passes about 200 g of stool per day, but during diarrhea, stool weight may exceed 250 g with 70–95% water. Stool frequency may increase to 5–20 times per day, and in severe cases, more than 1.4 litres of fluid may be lost.
Symptoms may range from mild discomfort and urgency to severe dehydration. Dysentery refers to painful, bloody diarrhea with low stool volume.
Common causes include contaminated food or water carrying bacteria (Shigella, Salmonella, Vibrio, E. coli), viruses (Norovirus, Rotavirus), poor hygiene, medications, irritable bowel syndrome, hyperthyroidism or intestinal diseases.
WHO Classification of Diarrhea
- Acute diarrhea: Lasts < 14 days (e.g., infectious diarrhea)
- Chronic diarrhea: Lasts > 14 days
Pathophysiology
Diarrhea results from imbalance between absorption and secretion of water and electrolytes. It can be due to intestinal disease or secondary to systemic illness.
Major mechanisms:
- Reduced sodium absorption
- Increased chloride secretion
- Increased intestinal motility
- Increased osmolarity inside the intestinal lumen
- Raised tissue hydrostatic pressure
- Malabsorption
Types of Diarrhea
1. Secretory Diarrhea
Occurs due to toxins from bacteria or viruses, or excess secretory mediators like serotonin and prostaglandins. Characterized by high stool output (> 500 mL/day) and persists even during fasting.
2. Osmotic Diarrhea
Caused by poorly absorbed substances creating an osmotic pull of water into the intestine. Examples include lactase deficiency, lactulose therapy and magnesium antacids. Symptoms reduce during fasting.
3. Exudative Diarrhea
Due to inflammation of intestinal mucosa, leading to loss of mucus, protein or blood. Seen in infections like Shigella or inflammatory bowel disease. Stools may be small volume but frequent, and may remain even during fasting.
4. Malabsorption Diarrhea
Improper absorption of nutrients causes bulky, fatty stools (steatorrhea). Stool volume decreases with fasting.
Management
The primary aim is to prevent dehydration and electrolyte loss. Treatment includes non-pharmacological and pharmacological measures.
Non-Pharmacological Management
- Eat a bland diet; avoid solid foods and dairy for at least 24 hours
- Rehydrate using Oral Rehydration Salts (ORS)
- Use WHO-formula ORS for best results
- Avoid ORS mixtures with very high electrolyte content as they may cause nausea and vomiting
- Homemade ORS:
- 200 mL boiled and cooled water
- 1 teaspoon sugar
- A pinch of salt
Pharmacological Management
1. Antimotility Drugs
These slow intestinal movement, allowing greater water absorption.
- Loperamide: Initial dose: 4 mg; then 2 mg after each loose stool Max dose: 16 mg/day
- Diphenoxylate: 5 mg four times a day Max dose: 20 mg/day
- Opium tincture: 0.6 mL four times daily (limited use due to addiction potential)
2. Adsorbents
Provide symptomatic relief by adsorbing toxins, nutrients and digestive juices. They reduce drug absorption when given with other medicines.
- Kaolin-pectin: 30–120 mL after each loose stool
3. Anti-Secretory Agents
Useful in traveler’s diarrhea.
- Bismuth subsalicylate – may cause black stool/tongue, tinnitus or neurotoxicity at high doses
4. Probiotics
Restore healthy intestinal flora and suppress pathogens.
- Lactobacillus acidophilus / L. bulgaricus Dose: 2 tablets or 1 sachet with milk/juice/water 3–4 times daily
5. Octreotide
Synthetic somatostatin analogue used for diarrhea associated with carcinoid and VIP-secreting tumors.
- Dose: 100–600 mcg/day in 2–4 divided subcutaneous injections
Side effects: nausea, abdominal pain, gallstones, diarrhea.
6. Antibacterial Agents
Used for bacterial infections causing mucosal injury and bloody diarrhea.
- Metronidazole / Tinidazole (anti-amoebic agents)
- Fluoroquinolones: Norfloxacin 400 mg Ciprofloxacin 500 mg Ofloxacin 200 mg
- Combination of fluoroquinolone + anti-amoebic agent is commonly used
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